Xamarin: how to Start an Application at Device Bootup in Android

This tutorial will explain to stat an application while the Android device boot-up. For this, we need to  listen to the BOOT_COMPLETED action and react to it.

BOOT_COMPLETED is a Broadcast Action that is broadcast once, after the system has finished booting. You can listen to this action by creating a BroadcastReceiver that then starts your launch Activity when it receives an intent with the BOOT_COMPLETED action.

Add this permission to your manifest

In your Android.Manifest you must add thi permission:

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

 

BackgroundTest-AndroidManifest

Then open this file and add the following rows under Application:

    <receiver android:name=".BootReceiver" android:enabled="true" 
              android:permission="android.permission.RECEIVE_BOOT_COMPLETED" >
      <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED" />
        <category android:name="android.intent.category.DEFAULT" />
      </intent-filter>
    </receiver>

In this example, we will create a new BroadcastReceiver called BootReceiver.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;

namespace BackgroundTest.Droid.BackgroundServices
{
    public class BootReceiver : BroadcastReceiver
    {
        public override void OnReceive(Context context, Intent intent)
        {
            Intent i = new Intent(context, typeof(MainActivity));
            i.AddFlags(ActivityFlags.NewTask);
            context.StartActivity(i);
        }
    }
}

Install the application, and then restart the device. You can see the application will start after the device restarts. An implementation of background services starting with Activity, it explains here.

Source code on GitHub.

Happy coding!

Preserve data when deploying Xamarin.Android app

By default all your data from your previous runs is deleted when you’re deploying an Xamarin.Android app. In many cases you don’t want the data to be deleted.

Visual Studio


To preserve data go to Tools -> Options -> Xamarin -> Android Settings and check “Preserve application data/cache on device between deploys”.

Preserve_data_visualstudio

Xamarin Studio


To preserve data go to Tools -> Options -> Android and check “Preserve data/cache between application deploys”.

Preserve_data_xamarinstudio

Happy coding!

Xamarin Forms and Google Mobile Ads for iOS

If you have a new Xamarin Project and you want to add an advertising, the simple way it is to use Google Admob. This implementation is only for Android and iOS.

One of the first things people think about when developing for a new platform / using a new technology is monetization; and in my case the question is: how easy is it to integrate AdMob? For Xamarin Forms the answer would be: “It depends” – it depends on luck & on the complexity of what you want to achieve; but I will detail this as we move along.

The first thing you need to do is add the required components to your projects. For this walktrough I will be using Visual Studio but it should be relatively the same when using Xamarin Studio. Here, things go separate ways for each of the platforms:

  • for Android – add the Google Play Services component
  • for iOS – add the AdMob component
  • for Windows Phone – download the SDK from here and add it as a reference

By now, you Android project should no longer be building & you should be receiving a COMPILETODALVIK : UNEXPECTED TOP-LEVEL error. To fix that, go into your Droid project properties, select the Android Options tab and then under Advanced modify the value for the Java Max Heap Size to 1G. Your project should now build without any errors.

Next, inside your shared / PCL project add a new Content View and call it AdMobView. Remove the code generated inside it’s constructor & it should look like this:

public class AdMobView : ContentView
{
    public AdMobView() { }
}

Add this new view to your page. In XAML you can do it like this:

<controls:AdMobView WidthRequest="320" HeightRequest="50" />

Make sure NOTHING interferes with the control. By nothing I mean – overlapping controls, page padding, control margins / spacing, etc. If you have something overlapping the ad control, ads will not display & you won’t receive an error, so be careful.

Android

Add a new class called AdMobRenderer with the code below. Make sure to keep the ExportRenderer attribute above the namespace, otherwise the magic won’t happen.

using WordBankEasy.Droid.Renderers;
using WordBankEasy.Views.AdMob;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(AdMobView), typeof(AdMobRenderer))]

namespace WordBankEasy.Droid.Renderers {
    public class AdMobRenderer : ViewRenderer<AdMobView, Android.Gms.Ads.AdView> {
        protected override void OnElementChanged(ElementChangedEventArgs<AdMobView> e) {
            base.OnElementChanged(e);

            if (Control == null) {
                var ad = new Android.Gms.Ads.AdView(Forms.Context);
                ad.AdSize = Android.Gms.Ads.AdSize.Banner;
                ad.AdUnitId = "ca-app-pub-4381168884554284/2250461656";

                var requestbuilder = new Android.Gms.Ads.AdRequest.Builder();
                ad.LoadAd(requestbuilder.Build());

                SetNativeControl(ad);
            }
        }
    }
}

Next, you need to modify your AndroidManifest.xml file to add the AdActivity & required permissions for displaying ads: ACCESS_NETWORK_STATE, INTERNET; just like in the example below (see also http://puresourcecode.com/dotnet/post/Android-required-permissions).

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <uses-sdk android:minSdkVersion="15" />
    <application>
    <activity android:name="com.google.android.gms.ads.AdActivity" 
            android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize" android:theme="@android:style/Theme.Translucent" />
    </application>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.INTERNET" />
</manifest>

That’s it. Your Android build should now display ads inside the AdMobView content view.

iOS

This, I haven’t got the chance to test yet as I don’t have a Mac around but people say it works, so I’ve added it for reference. Same as before, just add a new class called AdMobRenderer and copy-paste the code below but before you have to add a component.

In your iOS project click on “Components” (as in the picture)

Components

and click on “Get More Components…”. Then search admob and install it.

Google-Admob-Xamarin

using Xamarin.Forms;
using CoreGraphics;
using Xamarin.Forms.Platform.iOS;
using UIKit;
using WordBankEasy.Views.AdMob;
using WordBankEasy.iOS.Renderers;
using Google.MobileAds;

[assembly: ExportRenderer(typeof(AdMobView), typeof(AdMobRenderer))]
namespace WordBankEasy.iOS.Renderers {
    public class AdMobRenderer : ViewRenderer {
        const string AdmobID = "ca-app-pub-4381168884554284/5843056458";

        BannerView adView;
        bool viewOnScreen;

        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.View> e) {
            base.OnElementChanged(e);

            if (e.NewElement == null)
                return;

            if (e.OldElement == null) {
                adView = new BannerView(size: AdSizeCons.Banner, origin: new CGPoint(-10, 0)) {
                    AdUnitID = AdmobID,
                    RootViewController = UIApplication.SharedApplication.Windows[0].RootViewController
                };

                adView.AdReceived += (sender, args) => {
                    if (!viewOnScreen) this.AddSubview(adView);
                    viewOnScreen = true;
                };

                adView.LoadRequest(Request.GetDefaultRequest());
                base.SetNativeControl(adView);
            }
        }
    }
}

Here you can receive an strange error like:

Foundation.MonoTouchException: Objective-C exception thrown. Name: NSInvalidArgumentException Reason: -[AppDelegate window]: unrecognized selector sent to instance 0x7ffee9cdd4d0

Native stack trace:

0 CoreFoundation 0x000000010a12ed85 __exceptionPreprocess + 165

1 libobjc.A.dylib 0x000000010a5e3deb objc_exception_throw + 48

2 CoreFoundation 0x000000010a137d3d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205

3 CoreFoundation 0x000000010a07db17 forwarding + 487

4 CoreFoundation 0x000000010a07d8a8 _CF_forwarding_prep_0 + 120

5 WordBankEasyiOS 0x0000000100bc65e4 GADiTunesMetadataForFileAtPath + 4181

6 WordBankEasyiOS 0x0000000100c2d484 hasRequiredParams + 10260

7 WordBankEasyiOS 0x0000000100bc5f06 GADiTunesMetadataForFileAtPath + 2423

8 WordBankEasyiOS 0x0000000100bc1c35 GADCategories_NSURL_GADNSURLUtilities + 4438

9 WordBankEasyiOS 0x0000000100c00fde GADDispatchAsyncSafeMainQueue + 45

10 libobjc.A.dylib 0x000000010a5e4bff _class_initialize + 679

11 libobjc.A.dylib 0x000000010a5eacc5 lookUpImpOrForward + 176

12 libobjc.A.dylib 0x000000010a5f98bb objc_msgSend + 187

13 WordBankEasyiOS 0x0000000100bbe0ff GADCategories_DFPBannerView_CustomRenderedAd + 18074

14 WordBankEasyiOS 0x0000000100bbe382 GADCategories_DFPBannerView_CustomRenderedAd + 18717

15 WordBankEasyiOS 0x0000000100bbe527 GADCategories_DFPBannerView_CustomRenderedAd + 19138

16 ??? 0x000000011d368a0e 0x0 + 4785080846

17 ??? 0x000000011d36843b 0x0 + 4785079355

18 ??? 0x000000011d364d88 0x0 + 4785065352

19 ??? 0x000000011c51bbd6 0x0 + 4770085846

20 ??? 0x000000011c51b138 0x0 + 4770083128

21 ??? 0x000000011c51b138 0x0 + 4770083128

22 ??? 0x000000011c51b138 0x0 + 4770083128

Don't worry! I received the same error and I spend a lot of time to understand and fix it. There is a workaround that seems working fine.

In your iOS project, open AppDelegate.cs and add this code:

/// <summary>
/// Gets the window.
/// </summary>
/// <returns>UIWindow.</returns>
[Export("window")]
public UIWindow GetWindow() {
   return UIApplication.SharedApplication.Windows[0];
}

A complete example of this class is:

using System;
using System.Collections.Generic;
using System.Linq;

using Foundation;
using ImageCircle.Forms.Plugin.iOS;
using UIKit;

namespace WordBankEasy.iOS {
    // The UIApplicationDelegate for the application. This class is responsible for launching the 
    // User Interface of the application, as well as listening (and optionally responding) to 
    // application events from iOS.
    [Register("AppDelegate")]
    public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate {
        //
        // This method is invoked when the application has loaded and is ready to run. In this 
        // method you should instantiate the window, load the UI into it and then make the window
        // visible.
        //
        // You have 17 seconds to return from this method, or iOS will terminate your application.
        //
        public override bool FinishedLaunching(UIApplication app, NSDictionary options) {
            global::Xamarin.Forms.Forms.Init();

            ImageCircleRenderer.Init();

            LoadApplication(new App());

            return base.FinishedLaunching(app, options);
        }

        /// <summary>
        /// Gets the window.
        /// </summary>
        /// <returns>UIWindow.</returns>
        [Export("window")]
        public UIWindow GetWindow() {
            return UIApplication.SharedApplication.Windows[0];
        }
    }
}

After that you can start you app and see you advertising without problem. For now :)

Happy coding!

Android.Content.Res.Resources+NotFoundException: Resource ID #0x0

I've just created a simple MasterDetailPage and in the code I inserted an icon for the left page with:

public MainPage() {
    InitializeComponent();

    BackgroundColor = Color.FromHex("#007acc");
    Icon = "settings.png";
}

I tried to deploy my app on an Android emulator but I can't deploy it because Android.Content.Res.Resources+NotFoundException: Resource ID #0x0.

I checked everthing and evething seemed fine. The problem is the icon!

You have to remove Icon from the code and in the XAML page type the following code:

  <ContentPage.Icon>
    <OnPlatform x:TypeArguments="FileImageSource">
      <OnPlatform.iOS>settings.png</OnPlatform.iOS>
    </OnPlatform>
  </ContentPage.Icon>

Happy coding!

Installing Google Play Services in the Microsoft Visual Studio Android Emulator

Installing the Google Play Services in Microsoft’s Visual Studio Android Emulator that comes with Visual Studio 2015 is easy to do. This installs the Google Play store and related services, which makes it possible to install other apps to your Android image.

  1. Download the Google Apps package from the Team Android site. Make sure that you match the version of the apps to the version of Android that your emulator is for. The default emulator is for Kit Kat, but this also works for Lollipop.
  2. Start the Microsoft Visual Studio Android Emulator
  3. Start the Android virtual machine that matches the version of the apps that you downloaded for (default would be Kit Kat).
  4. Unlock the Android VM so you get to the home screen
  5. Drag and drop the downloaded Google Apps package in to the Android VM. You will get a prompt to install the apps that looks like this: Install-Goople-Play-Microsoft-Android-Emulator
  6. Select the “Install and Shut Down” option.
  7. Start the VM again
  8. Click the All Apps button in Android and you will see the Google Play store.
  9. When you open the Google Play store, you will need to login with your Google account and make a new one.

Once you have the Google Play store installed, you should be able to install other common applications. I tested this by installing Chrome and it worked well.

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