Google Launches Android Studio 2.0 With Improved Android Emulator And New Instant Run Feature

Google-Android-Studio-v2

Google today launched version 2.0 of its Android Studio integrated development environment (IDE) for writing apps for its mobile operating system.

Android Studio, which is based on IntelliJ, launched back in 2013 and came out of beta a year ago. It includes everything a developer needs to build an app, including a code editor, code analysis tools, emulators for all of Google’s Android platforms, and more.

The new version is now available as a preview in the Canary release channel of Android Studio.

With version 2.0, as Google’s group product manager for Android Studio Stephanie Cuthbertson told me, the team wanted to build on the foundation it laid over the last two years and focus on speed. “For the IDE to be delightful, it doesn’t just have to be stable — but amazingly stabled,” she told me. The team felt that it achieved this with the last couple of releases.

androidstudio2-0_instantrun

With this update, Google massively accelerated deployment speeds, for example. Cuthbertson tells me that a full build is now 2x to 2.5x faster than in previous releases. That’s a huge step forward, but what developers will likely appreciate even more in this new version is the addition of a new feature called “Instant Run.” This almost mimics the experience of writing HTML, where you write your code, reload your browser and see what changed. On mobile, that process typically takes quite a bit longer, even with the improved build speeds.

Instant Run lets developers build and deploy their apps once (both to the emulator or to a physical device) and then as they change their code and deploy it, it’ll only take a second or two before they can see those changes in the running app. This feature will work for all apps that target Ice Cream Sandwich and later. Cuthbertson politely refused to tell us how exactly Instant Run works, but promised that Google will detail the technology behind this feature in the future.

Given the size of the Android ecosystem, it’s almost impossible for most developers to test their apps on even the most popular devices early on in the development phase. With services like Xamarin Test Cloud, the AWS Device Farm and Google’s own Test Lab, developers have plenty of options to test their apps later on, but during the development process, most of the testing happens with the help of emulators. Google’s own emulator wasn’t always the fastest and easiest to use (to the point where Microsoft ended up releasing its own).

androidstudio2_emulator

With this update, Google is introducing new emulators that, given modern hardware, should run faster than any physical device. The team also rebuilt the interface, so that it’s now easy to trigger typical actions like firing up the camera. Developers will also be able to emulate different network conditions and emulate the GPS (even with pre-configured paths). The emulator also includes access to all the standard Google Play services. Maybe more importantly, though, you can now simply resize the emulator window to test different screen sizes.

For developers who build graphics-intensive apps and games, the Studio now also includes a new GPU profiler. This will allow developers to see exactly what’s happening every time the screen draws a new image to trace performance issues, for example. This tool is still officially in preview.

androidstudio2-0_gpuprofiler_preview

Change a character in a list of list with PowerShell

How do I delete certain characters or replace certain characters with other characters by some batch file execution, for filenames of all files in a Windows folder in one go, is there a PowerShell command for that?

I've shown how to batch rename all the files and directories in the current directory that contain spaces by replacing them with _ underscores.

Dir | Rename-Item -NewName { $_.Name -replace "-", "_" }

Optionally, the Where-Object command can be used to filter out ineligible objects for the successive cmdlet (command-let). The following are some examples to illustrate the flexibility it can afford you:

To skip any document files

Dir |
Where-Object { $_.Name -notmatch "\.(doc|xls|ppt)x?$" } |
Rename-Item -NewName { $_.Name -replace " ","_" }

To process only directories (pre-3.0 version)

Dir |
Where-Object { $_.Mode -match "^d" } |
Rename-Item -NewName { $_.Name -replace " ","_" }

PowerShell v3.0 introduced new Dir flags. You can also use Dir -Directory there.

To skip any files already containing an underscore (or some other character)

Dir |
Where-Object { -not $_.Name.Contains("_") } |
Rename-Item -NewName { $_.Name -replace " ","_" }

Happy coding!

Implementing the Inversion of Control Pattern in C#

In my previous post I spoke about the first principle of SOLID. In this post I explain last two principle. I hope it will be clear enough.

Dependency Inversion Principle (DIP)

Dependency Injection Principle states that there should be more abstraction between the higher level module and the lower level module. It is required to have loose coupling so that any change in the low level modules will not affect or there will be minimal impact at the higher level module. The ideal scenario would be when you write components for other applications to consume.

Inversion-of-Control-Pattern-1

In the example provided in Fig 1.0 VehicleController is the higher level module, which consumes and uses the lower level module Car. If you want to change the vehicle to Truck instead of Car then VehicleController does not require any change if there is higher level of abstraction.

Inversion of Control (IoC)

Inversion of Control is a technique to implement the Dependency Inversion Principle in C#. Inversion of control can be achieved by using interfaces or abstract class. The rule is that the lower level modules should sign up the contract to a single interface and the higher level module will consume only modules that are implementing the interface. This technique removes the dependency between the modules.

Inversion-of-Control-Pattern

As shown in Fig 2.0 Car and Truck will implement the interface IVehicle and VehicleController will couple with the vehicles through the IVehicle interface thus increasing the level of abstraction between the layers.

Sample IoC implementation in C#

In this section we will see the implementation of the IoC technique in the C# language. In Visual Studio create a Console application project and name it IoCDemo. Now add classes named VehicleController, Car, Truck and an interface IVehicle. In a real work scenario these items will be in separate layers like Car and Truck in one layer, IVehicle interface in abstraction layer and VehicleController as the higher level module. I have clubbed everything into a single project as it is a sample code. Following is the sample C# code implementing IoC.

public class Car : IVehicle
{

    #region IVehicle Members

    public void Accelerate()
    {
        Console.WriteLine("Car accelerates...");
    }

    public void Brake()
    {
        Console.WriteLine("Car stopped.");
    }

    #endregion
}

public class Truck : IVehicle
{
    #region IVehicle Members

    public void Accelerate()
    {
        Console.WriteLine("Truck accelerates...");
    }

    public void Brake()
    {
        Console.WriteLine("Truck stopped.");
    }

    #endregion
}

public interface IVehicle
{
    void Accelerate();
    void Brake();
}

public class VehicleController
{
    IVehicle m_Vehicle;

    public VehicleController(IVehicle vehicle)
    {
        this.m_Vehicle = vehicle;
    }

    public void Accelerate()
    {
        m_Vehicle.Accelerate();
    }

    public void Brake()
    {
        m_Vehicle.Brake();
    }
}

class Program
{
    static void Main(string[] args)
    {
        IVehicle vehicle = new Car();
        //IVehicle vehicle = new Truck();

        VehicleController vehicleController = new VehicleController(vehicle);
        vehicle.Accelerate();
        vehicle.Brake();

        Console.Read();
    }
}

In the above code the products are completely decoupled from the consumer using the IVehicle interface. The object is injected into the constructor of the VehicleController class in reference with the interface IVehicle. The constructor where the object gets injected is called as Injection Constructor.

Inversion of Control Container

If you look at the code sample provided in the above section, the Car or Truck object creation is still present in the Main method, which is again a dependency. In IoC technique the creation of the object will also be delegated to a separate component or framework, which will take care of creating and injecting the dependency object. This is called dependency injection and the component accomplishing the task is called the IoC container.

There are many IoC containers readily available in the market; some of the popular ones are the following.

  1. Microsoft Unity framework
  2. Castle Windsor
  3. NInject

You can also create your own custom IoC container using reflection and generics in C#. I hope this article has provided enough information about the Inversion of Control pattern.

Happy coding!

SOLID principles in C#

SOLID is an acronym and stands for 5 important object oriented principles. The SOLID principles help in making the object oriented application source code robust, scalable, extensible and non-fragile. It is absolutely necessary when you have a layered architecture and they are bound to changes over the period of time. Following are the 5 principles.

  1. Single Responsibility Principle
  2. Open Closed Principle
  3. Liskov Substitution Principle
  4. Interface Segregation Principle
  5. Dependency Inversion Principle

In this article I will take you through all three all five SOLID principles and also provide sample C# code to demonstrate them.

Single Responsibility Principle (SRP)

SRP states that every class should have a single responsibility, and that responsibility should be entirely encapsulated by the class. There should only be a single reason for making the change to a class.

It means that a class should not be loaded with multiple responsibilities and a single responsibility should not be scattered across multiple classes and mixed with other responsibilities. The reason is that the more changes requested in the future, the more changes the class needs to undergo.

Below is a code violating the SRP. In the sample code, SRP is violated by mixing the OpenGate and CloseGate responsibility with the core vehicle service functionality.

public class ServiceStation
{
    public void OpenGate()
    {
        //Open the gate if the time is later than 9 AM
    }

    public void DoService(Vehicle vehicle)
    {
        //Check if service station is opened and then
        //complete the vehicle service
    }

    public void CloseGate()
    {
        //Close the gate if the time has crossed 6PM
    }
}

The re-factored code sample is as follows. A new interface is created and the gate related utility methods are moved to a different class called ServiceStationUtility.

public class ServiceStation
{
    IGateUtility _gateUtility;

    public ServiceStation(IGateUtility gateUtility)
    {
        this._gateUtility = gateUtility;
    }
    public void OpenForService()
    {
        _gateUtility.OpenGate();
    }

    public void DoService()
    {
        //Check if service station is opened and then
        //complete the vehicle service
    }

    public void CloseForDay()
    {
        _gateUtility.CloseGate();
    }
}

public class ServiceStationUtility : IGateUtility
{
    public void OpenGate()
    {
        //Open the shop if the time is later than 9 AM
    }

    public void CloseGate()
    {
        //Close the shop if the time has crossed 6PM
    }
}

public interface IGateUtility
{
    void OpenGate();
    void CloseGate();
}

Open Closed Principle (OCP)

OCP states that software application source codes should be open for extension but should be closed for modification.

According to the OCP principle the code should be easily extensible but it should not need any changes to be done to the core implementations. Following is a C# source code violating OCP where a new car has to be added then it will require changes in the core function CalculateMileage.

public class MileageCalculator
{
    IEnumerable<car> _cars;
    public MileageCalculator(IEnumerable<car> cars) { this._cars = cars; }

    public void CalculateMileage()
    {
        foreach (var car in _cars)
        {
            if (car.Name == "Audi")
                Console.WriteLine("Mileage of the car {0} is {1}", car.Name, "10M");
            else if (car.Name == "Mercedes")
                Console.WriteLine("Mileage of the car {0} is {1}", car.Name, "20M");
        }
    }
}

The OCP violation can be fixed as shown below, using an interface and creating classes for each car there, by reducing making the CalculateMileage method more generic and extensible.

public class MileageCalculator
{
    IEnumerable<car> _cars;
    public MileageCalculator(IEnumerable<car> cars) { this._cars = cars; }

    public void CalculateMileage()
    {
        CarController controller = new CarController();
        foreach (var car in _cars)
        {
            Console.WriteLine("Mileage of the car {0} is {1}", car.Name, controller.GetCarMileage(car.Name));
        }
    }
}

public class CarController
{
    List<icar> cars;
    public CarController()
    {
        cars = new List<icar>();
        cars.Add(new Audi());
        cars.Add(new Mercedes());
    }

    public string GetCarMileage(string name)
    {
        return cars.First(car => car.Name == name).GetMileage();
    }
}

public interface ICar
{
    string Name { get; set; }
    string GetMileage();
}

public class Audi : ICar
{
    public string Name { get; set; }

    public string GetMileage()
    {
        return "10M";
    }
}

public class Mercedes : ICar
{
    public string Name { get; set; }

    public string GetMileage()
    {
        return "20M";
    }
}

Liskov Substitution Principle (LSP)

LSP states that the derived classes should be perfectly substitutable for their base classes. If class D is derived from A then D should be substitutable for A.

Look at the following C# code sample where the LSP is broken. Simply, an Orange cannot substitute an Apple, which results in printing the color of apple as Orange.

namespace SolidDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Apple apple = new Orange();
            Console.WriteLine(apple.GetColor());
        }
    }

    public class Apple
    {
        public virtual string GetColor()
        {
            return "Red";
        }
    }

    public class Orange : Apple
    {
        public override string GetColor()
        {
            return "Orange";
        }
    }
}

Now let us re-factor and make it comply with LSP by having a generic base class for both Apple and Orange.

namespace SolidDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Fruit fruit = new Orange();
            Console.WriteLine(fruit.GetColor());
            fruit = new Apple();
            Console.WriteLine(fruit.GetColor());
        }
    }

    public abstract class Fruit
    {
        public abstract string GetColor();
    }

    public class Apple : Fruit
    {
        public override string GetColor()
        {
            return "Red";
        }
    }

    public class Orange : Apple
    {
        public override string GetColor()
        {
            return "Orange";
        }
    }
}

Interface Segregation Principle (ISP)

ISP states that no clients should be forced to implement methods which it does not use and the contracts should be broken down to thin ones.

Say for example when a thick interface is defined declaring a wide responsibility of members then there will be opportunities where some clients may have to implement members, which they don’t even use. In the below mentioned example ISP is violated where ProcessCreditCard method is not required by InpersonOrder class but is forced to implement.

public interface IOrder
{
    void Purchase();
    void ProcessCreditCard();
}

public class OnlineOrder : IOrder
{
    public void Purchase()
    {
        //Do purchase
    }

    public void ProcessCreditCard()
    {
        //process through credit card
    }
}

public class InpersionOrder : IOrder
{
    public void Purchase()
    {
        //Do purchase
    }

    public void ProcessCreditCard()
    {
        //Not required for inperson purchase
        throw new NotImplementedException();
    }
}

Now let us fix the violation by breaking down the IOrder interface.

public interface IOrder
{
    void Purchase();
}

public interface IOnlineOrder
{
    void ProcessCreditCard();
}

public class OnlineOrder : IOrder, IOnlineOrder
{
    public void Purchase()
    {
        //Do purchase
    }

    public void ProcessCreditCard()
    {
        //process through credit card
    }
}

public class InpersionOrder : IOrder
{
    public void Purchase()
    {
        //Do purchase
    }
}

Dependency Inversion Principle (DIP)

DIP states that the higher level modules should be coupled with the lower level modules with complete abstraction.

You can read more about DIP and IoC please check here.

How to generate a random password

These code samples demonstrate how to generate a strong random password, which does not contain ambiguous characters (such as [1,l,I] or [O,0]). A strong password must be at least eight characters long and contain a combination of lower- and upper-case letters, numbers, and special characters.

///////////////////////////////////////////////////////////////////////////////
// SAMPLE: Generates random password, which complies with the strong password
//         rules and does not contain ambiguous characters.
//
// To run this sample, create a new Visual C# project using the Console
// Application template and replace the contents of the Class1.cs file with
// the code below.
//
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND,
// EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
// 
// Copyright (C) 2015 PureSourceCode. All rights reserved.
// 
using System;
using System.Security.Cryptography;

/// <summary>
/// This class can generate random passwords, which do not include ambiguous 
/// characters, such as I, l, and 1. The generated password will be made of
/// 7-bit ASCII symbols. Every four characters will include one lower case
/// character, one upper case character, one number, and one special symbol
/// (such as '%') in a random order. The password will always start with an
/// alpha-numeric character; it will not start with a special symbol (we do
/// this because some back-end systems do not like certain special
/// characters in the first position).
/// </summary>
public class RandomPassword
{
    // Define default min and max password lengths.
    private static int DEFAULT_MIN_PASSWORD_LENGTH  = 8;
    private static int DEFAULT_MAX_PASSWORD_LENGTH  = 10;

    // Define supported password characters divided into groups.
    // You can add (or remove) characters to (from) these groups.
    private static string PASSWORD_CHARS_LCASE  = "abcdefgijkmnopqrstwxyz";
    private static string PASSWORD_CHARS_UCASE  = "ABCDEFGHJKLMNPQRSTWXYZ";
    private static string PASSWORD_CHARS_NUMERIC= "23456789";
    private static string PASSWORD_CHARS_SPECIAL= "*$-+?_&=!%{}/";

    /// <summary>
    /// Generates a random password.
    /// </summary>
    /// <returns>
    /// Randomly generated password.
    /// </returns>
    /// <remarks>
    /// The length of the generated password will be determined at
    /// random. It will be no shorter than the minimum default and
    /// no longer than maximum default.
    /// </remarks>
    public static string Generate()
    {
        return Generate(DEFAULT_MIN_PASSWORD_LENGTH, 
                        DEFAULT_MAX_PASSWORD_LENGTH);
    }

    /// <summary>
    /// Generates a random password of the exact length.
    /// </summary>
    /// <param name="length">
    /// Exact password length.
    /// </param>
    /// <returns>
    /// Randomly generated password.
    /// </returns>
    public static string Generate(int length)
    {
        return Generate(length, length);
    }

    /// <summary>
    /// Generates a random password.
    /// </summary>
    /// <param name="minLength">
    /// Minimum password length.
    /// </param>
    /// <param name="maxLength">
    /// Maximum password length.
    /// </param>
    /// <returns>
    /// Randomly generated password.
    /// </returns>
    /// <remarks>
    /// The length of the generated password will be determined at
    /// random and it will fall with the range determined by the
    /// function parameters.
    /// </remarks>
    public static string Generate(int   minLength,
                                  int   maxLength)
    {
        // Make sure that input parameters are valid.
        if (minLength <= 0 || maxLength <= 0 || minLength > maxLength)
            return null;

        // Create a local array containing supported password characters
        // grouped by types. You can remove character groups from this
        // array, but doing so will weaken the password strength.
        char[][] charGroups = new char[][] 
        {
            PASSWORD_CHARS_LCASE.ToCharArray(),
            PASSWORD_CHARS_UCASE.ToCharArray(),
            PASSWORD_CHARS_NUMERIC.ToCharArray(),
            PASSWORD_CHARS_SPECIAL.ToCharArray()
        };

        // Use this array to track the number of unused characters in each
        // character group.
        int[] charsLeftInGroup = new int[charGroups.Length];

        // Initially, all characters in each group are not used.
        for (int i=0; i<charsLeftInGroup.Length; i++)
            charsLeftInGroup[i] = charGroups[i].Length;
        
        // Use this array to track (iterate through) unused character groups.
        int[] leftGroupsOrder = new int[charGroups.Length];

        // Initially, all character groups are not used.
        for (int i=0; i<leftGroupsOrder.Length; i++)
            leftGroupsOrder[i] = i;

        // Because we cannot use the default randomizer, which is based on the
        // current time (it will produce the same "random" number within a
        // second), we will use a random number generator to seed the
        // randomizer.
        
        // Use a 4-byte array to fill it with random bytes and convert it then
        // to an integer value.
        byte[] randomBytes = new byte[4];

        // Generate 4 random bytes.
        RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
        rng.GetBytes(randomBytes);

        // Convert 4 bytes into a 32-bit integer value.
        int seed = BitConverter.ToInt32(randomBytes, 0);

        // Now, this is real randomization.
        Random  random  = new Random(seed);

        // This array will hold password characters.
        char[] password = null;

        // Allocate appropriate memory for the password.
        if (minLength < maxLength)
            password = new char[random.Next(minLength, maxLength+1)];
        else
            password = new char[minLength];

        // Index of the next character to be added to password.
        int nextCharIdx;
        
        // Index of the next character group to be processed.
        int nextGroupIdx;

        // Index which will be used to track not processed character groups.
        int nextLeftGroupsOrderIdx;
        
        // Index of the last non-processed character in a group.
        int lastCharIdx;

        // Index of the last non-processed group.
        int lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
        
        // Generate password characters one at a time.
        for (int i=0; i<password.Length; i++)
        {
            // If only one character group remained unprocessed, process it;
            // otherwise, pick a random character group from the unprocessed
            // group list. To allow a special character to appear in the
            // first position, increment the second parameter of the Next
            // function call by one, i.e. lastLeftGroupsOrderIdx + 1.
            if (lastLeftGroupsOrderIdx == 0)
                nextLeftGroupsOrderIdx = 0;
            else
                nextLeftGroupsOrderIdx = random.Next(0, 
                                                     lastLeftGroupsOrderIdx);

            // Get the actual index of the character group, from which we will
            // pick the next character.
            nextGroupIdx = leftGroupsOrder[nextLeftGroupsOrderIdx];

            // Get the index of the last unprocessed characters in this group.
            lastCharIdx = charsLeftInGroup[nextGroupIdx] - 1;
            
            // If only one unprocessed character is left, pick it; otherwise,
            // get a random character from the unused character list.
            if (lastCharIdx == 0)
                nextCharIdx = 0;
            else
                nextCharIdx = random.Next(0, lastCharIdx+1);

            // Add this character to the password.
            password[i] = charGroups[nextGroupIdx][nextCharIdx];
            
            // If we processed the last character in this group, start over.
            if (lastCharIdx == 0)
                charsLeftInGroup[nextGroupIdx] = 
                                          charGroups[nextGroupIdx].Length;
            // There are more unprocessed characters left.
            else
            {
                // Swap processed character with the last unprocessed character
                // so that we don't pick it until we process all characters in
                // this group.
                if (lastCharIdx != nextCharIdx)
                {
                    char temp = charGroups[nextGroupIdx][lastCharIdx];
                    charGroups[nextGroupIdx][lastCharIdx] = 
                                charGroups[nextGroupIdx][nextCharIdx];
                    charGroups[nextGroupIdx][nextCharIdx] = temp;
                }
                // Decrement the number of unprocessed characters in
                // this group.
                charsLeftInGroup[nextGroupIdx]--;
            }

            // If we processed the last group, start all over.
            if (lastLeftGroupsOrderIdx == 0)
                lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
            // There are more unprocessed groups left.
            else
            {
                // Swap processed group with the last unprocessed group
                // so that we don't pick it until we process all groups.
                if (lastLeftGroupsOrderIdx != nextLeftGroupsOrderIdx)
                {
                    int temp = leftGroupsOrder[lastLeftGroupsOrderIdx];
                    leftGroupsOrder[lastLeftGroupsOrderIdx] = 
                                leftGroupsOrder[nextLeftGroupsOrderIdx];
                    leftGroupsOrder[nextLeftGroupsOrderIdx] = temp;
                }
                // Decrement the number of unprocessed groups.
                lastLeftGroupsOrderIdx--;
            }
        }

        // Convert password characters into a string and return the result.
        return new string(password);
     }
}

/// <summary>
/// Illustrates the use of the RandomPassword class.
/// </summary>
public class RandomPasswordTest
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main(string[] args)
    {
        // Print 100 randomly generated passwords (8-to-10 char long).
        for (int i=0; i<100; i++)
            Console.WriteLine(RandomPassword.Generate(8, 10));
    }
}

VB.NET code sample

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' SAMPLE: Generates random password, which complies with the strong password
'         rules and does not contain ambiguous characters.
'
' To run this sample, create a new Visual Basic.NET project using the Console
' Application template and replace the contents of the Module1.vb file with
' the code below.
'
' THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND,
' EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
' WARRANTIES OF MERCHANTABILITY AND'OR FITNESS FOR A PARTICULAR PURPOSE.
' 
' Copyright (C) 2015 PureSourceCode. All rights reserved.
' 
 Imports System
 Imports System.Security.Cryptography

 Module Module1

' <summary>
' This class can generate random passwords, which do not include ambiguous 
' characters, such as I, l, and 1. The generated password will be made of
' 7-bit ASCII symbols. Every four characters will include one lower case
' character, one upper case character, one number, and one special symbol
' (such as '%') in a random order. The password will always start with an
' alpha-numeric character; it will not start with a special symbol (we do
' this because some back-end systems do not like certain special
' characters in the first position).
' </summary>
Public Class RandomPassword

    ' Define default min and max password lengths.
    Private Shared DEFAULT_MIN_PASSWORD_LENGTH As Integer = 8
    Private Shared DEFAULT_MAX_PASSWORD_LENGTH As Integer = 10

    ' Define supported password characters divided into groups.
    ' You can add (or remove) characters to (from) these groups.
    Private Shared PASSWORD_CHARS_LCASE As String  = "abcdefgijkmnopqrstwxyz"
    Private Shared PASSWORD_CHARS_UCASE As String  = "ABCDEFGHJKLMNPQRSTWXYZ"
    Private Shared PASSWORD_CHARS_NUMERIC As String= "23456789"
    Private Shared PASSWORD_CHARS_SPECIAL As String= "*$-+?_&=!%{}/"

    ' <summary>
    ' Generates a random password.
    ' </summary>
    ' <returns>
    ' Randomly generated password.
    ' </returns>
    ' <remarks>
    ' The length of the generated password will be determined at
    ' random. It will be no shorter than the minimum default and
    ' no longer than maximum default.
    ' </remarks>
    Public Shared Function Generate() As String
        Generate = Generate(DEFAULT_MIN_PASSWORD_LENGTH, _
                            DEFAULT_MAX_PASSWORD_LENGTH)
    End Function

    ' <summary>
    ' Generates a random password of the exact length.
    ' </summary>
    ' <param name="length">
    ' Exact password length.
    ' </param>
    ' <returns>
    ' Randomly generated password.
    ' </returns>
    Public Shared Function Generate(length As Integer) As String
        Generate = Generate(length, length)
    End Function

    ' <summary>
    ' Generates a random password.
    ' </summary>
    ' <param name="minLength">
    ' Minimum password length.
    ' </param>
    ' <param name="maxLength">
    ' Maximum password length.
    ' </param>
    ' <returns>
    ' Randomly generated password.
    ' </returns>
    ' <remarks>
    ' The length of the generated password will be determined at
    ' random and it will fall with the range determined by the
    ' function parameters.
    ' </remarks>
    Public Shared Function Generate(minLength As Integer, _
                                    maxLength As Integer) _
        As String

        ' Make sure that input parameters are valid.
        If (minLength <= 0 Or maxLength <= 0 Or minLength > maxLength) Then
            Generate = Nothing
        End If

        ' Create a local array containing supported password characters
        ' grouped by types. You can remove character groups from this
        ' array, but doing so will weaken the password strength.
        Dim charGroups As Char()() = New Char()() _
        { _
            PASSWORD_CHARS_LCASE.ToCharArray(), _
            PASSWORD_CHARS_UCASE.ToCharArray(), _
            PASSWORD_CHARS_NUMERIC.ToCharArray(), _
            PASSWORD_CHARS_SPECIAL.ToCharArray() _
        }

        ' Use this array to track the number of unused characters in each
        ' character group.
        Dim charsLeftInGroup As Integer() = New Integer(charGroups.Length-1){}

        ' Initially, all characters in each group are not used.
        Dim I As Integer
        For I=0 To charsLeftInGroup.Length-1
            charsLeftInGroup(I) = charGroups(I).Length
        Next

        ' Use this array to track (iterate through) unused character groups.
        Dim leftGroupsOrder As Integer()  = New Integer(charGroups.Length-1){}

        ' Initially, all character groups are not used.
        For I=0 To leftGroupsOrder.Length-1
            leftGroupsOrder(I) = I
        Next

        ' Because we cannot use the default randomizer, which is based on the
        ' current time (it will produce the same "random" number within a
        ' second), we will use a random number generator to seed the
        ' randomizer.
        
        ' Use a 4-byte array to fill it with random bytes and convert it then
        ' to an integer value.
        Dim randomBytes As Byte() = New Byte(3){}

        ' Generate 4 random bytes.
        Dim rng As RNGCryptoServiceProvider = New RNGCryptoServiceProvider()

        rng.GetBytes(randomBytes)

        ' Convert 4 bytes into a 32-bit integer value.
        Dim seed As Integer = BitConverter.ToInt32(randomBytes, 0)

        ' Now, this is real randomization.
        Dim random As Random = New Random(seed)

        ' This array will hold password characters.
        Dim password As Char() = Nothing

        ' Allocate appropriate memory for the password.
        If (minLength < maxLength) Then
            password = New Char(random.Next(minLength-1, maxLength)){}
        Else
            password = New Char(minLength-1){}
        End If

        ' Index of the next character to be added to password.
        Dim nextCharIdx             As Integer

        ' Index of the next character group to be processed.
        Dim nextGroupIdx            As Integer

        ' Index which will be used to track not processed character groups.
        Dim nextLeftGroupsOrderIdx  As Integer

        ' Index of the last non-processed character in a group.
        Dim lastCharIdx             As Integer

        ' Index of the last non-processed group.
        Dim lastLeftGroupsOrderIdx As Integer = leftGroupsOrder.Length-1

        ' Generate password characters one at a time.
        For I=0 To password.Length-1

            ' If only one character group remained unprocessed, process it;
            ' otherwise, pick a random character group from the unprocessed
            ' group list. To allow a special character to appear in the
            ' first position, increment the second parameter of the Next
            ' function call by one, i.e. lastLeftGroupsOrderIdx + 1.
            If (lastLeftGroupsOrderIdx = 0) Then
                nextLeftGroupsOrderIdx = 0
            Else
                nextLeftGroupsOrderIdx = random.Next(0, lastLeftGroupsOrderIdx)
            End If

            ' Get the actual index of the character group, from which we will
            ' pick the next character.
            nextGroupIdx = leftGroupsOrder(nextLeftGroupsOrderIdx)

            ' Get the index of the last unprocessed characters in this group.
            lastCharIdx = charsLeftInGroup(nextGroupIdx)-1

            ' If only one unprocessed character is left, pick it; otherwise,
            ' get a random character from the unused character list.
            If (lastCharIdx = 0) Then
                nextCharIdx = 0
            Else
                nextCharIdx = random.Next(0, lastCharIdx+1)
            End If

            ' Add this character to the password.
            password(I) = charGroups(nextGroupIdx)(nextCharIdx)
            
            ' If we processed the last character in this group, start over.
            If (lastCharIdx = 0) Then
                charsLeftInGroup(nextGroupIdx) = _
                                charGroups(nextGroupIdx).Length
            ' There are more unprocessed characters left.
            Else
                ' Swap processed character with the last unprocessed character
                ' so that we don't pick it until we process all characters in
                ' this group.
                If (lastCharIdx <> nextCharIdx) Then
                    Dim temp As Char = charGroups(nextGroupIdx)(lastCharIdx)
                    charGroups(nextGroupIdx)(lastCharIdx) = _ 
                                charGroups(nextGroupIdx)(nextCharIdx)
                    charGroups(nextGroupIdx)(nextCharIdx) = temp
                End If

                ' Decrement the number of unprocessed characters in
                ' this group.
                charsLeftInGroup(nextGroupIdx) = _
                           charsLeftInGroup(nextGroupIdx)-1
            End If

            ' If we processed the last group, start all over.
            If (lastLeftGroupsOrderIdx = 0) Then
                lastLeftGroupsOrderIdx = leftGroupsOrder.Length-1
            ' There are more unprocessed groups left.
            Else
                ' Swap processed group with the last unprocessed group
                ' so that we don't pick it until we process all groups.
                If (lastLeftGroupsOrderIdx <> nextLeftGroupsOrderIdx) Then
                    Dim temp As Integer = _
                                leftGroupsOrder(lastLeftGroupsOrderIdx)
                    leftGroupsOrder(lastLeftGroupsOrderIdx) = _ 
                                leftGroupsOrder(nextLeftGroupsOrderIdx)
                    leftGroupsOrder(nextLeftGroupsOrderIdx) = temp
                End If
                
                ' Decrement the number of unprocessed groups.
                lastLeftGroupsOrderIdx = lastLeftGroupsOrderIdx - 1
            End If
        Next

        ' Convert password characters into a string and return the result.
        Generate = New String(password)
    End Function

End Class

' <summary>
' The main entry point for the application.
' </summary>
Sub Main()
    Dim I As Integer
    For I=1 To 100
        Console.WriteLine(RandomPassword.Generate(8, 10))
    Next
End Sub

End Module

Program output

B$g3-6YpjA
Nk5{!Yb37
P}o8wX7$!
Dc5+t=Q8}P
gG_2?a4H
yW}5K3w*9
Qr9%5-jHg
8Bg%s*A63q
3Nd?E{5jxY
2Kf!s}E9
3z$XN9q*+
...
T!b68C*wt

How to use REPLACE() within NTEXT columns in SQL Server

SQL has an incredibly useful function, REPLACE(), which replaces all occurrences of a specified string with another string, returning a new string. It works great with all forms of NCHAR and NVARCHAR fields. It does not, however, work with NTEXT fields.

Fear not — there’s an easy workaround, thanks to type-casting and SQL 2005’s NVARCHAR(max) datatype. Here’s the process in an nutshell.

  1. Cast the NTEXT field to the NVARCHAR(max) datatype using the CAST function.
  2. Perform your REPLACE on the output of #1.
  3. Cast the output of #2 back to NTEXT. (Not really required, but it does get us back to where we started.

A simple SQL query illustrates this.

select cast(replace(cast(myntext as nvarchar(max)),'find','replace') as ntext)
from myntexttable

If you’re using SQL 2000, you’re out of luck, as NVARCHAR(max) first appeared in SQL 2005. However, if your NTEXT field is less than 8000 characters, you can cast it to VARCHAR(8000) — the largest possible VARCHAR size — to accomplish the same.

[Note #1: This solution below will also work with TEXT fields. Simply replace NTEXT with TEXT, and NVARCHAR with VARCHAR.]

[Note #2: NTEXT fields are depreciated in SQL 2005 in favor of NVARCHAR(max), so avoid using NTEXT and you’ll avoid this problem altogether in the future.]

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