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Working with the Android Manifest

  • Artikkeli

AndroidManifest.xml is a powerful file in the Android platform that allows you to describe the functionality and requirements of your application to Android. However, working with it is not easy. Xamarin.Android helps to minimize this difficulty by allowing you to add custom attributes to your classes, which will then be used to automatically generate the manifest for you. Our goal is that 99% of our users should never need to manually modify AndroidManifest.xml.

AndroidManifest.xml is generated as part of the build process, and the XML found within Properties/AndroidManifest.xml is merged with XML that is generated from custom attributes. The resulting merged AndroidManifest.xml resides in the obj subdirectory; for example, it resides at obj/Debug/android/AndroidManifest.xml for Debug builds. The merging process is trivial: it uses custom attributes within the code to generate XML elements, and inserts those elements into AndroidManifest.xml.

The Basics

At compile time, assemblies are scanned for non-abstract classes that derive from Activity and have the [Activity] attribute declared on them. It then uses these classes and attributes to build the manifest. For example, consider the following code:

namespace Demo
{
    public class MyActivity : Activity
    {
    }
}

This results in nothing being generated in AndroidManifest.xml. If you want an <activity/> element to be generated, you need to use the [Activity] custom attribute:

namespace Demo
{
    [Activity]
    public class MyActivity : Activity
    {
    }
}

This example causes the following xml fragment to be added to AndroidManifest.xml:

<activity android:name="md5a7a3c803e481ad8926683588c7e9031b.MainActivity" />

The [Activity] attribute has no effect on abstract types; abstract types are ignored.

Activity Name

Beginning with Xamarin.Android 5.1, the type name of an activity is based on the MD5SUM of the assembly-qualified name of the type being exported. This allows the same fully-qualified name to be provided from two different assemblies and not get a packaging error. (Before Xamarin.Android 5.1, the default type name of the activity was created from the lowercased namespace and the class name.)

If you wish to override this default and explicitly specify the name of your activity, use the Name property:

[Activity (Name="awesome.demo.activity")]
public class MyActivity : Activity
{
}

This example produces the following xml fragment:

<activity android:name="awesome.demo.activity" />

Note

You should use the Name property only for backward-compatibility reasons, as such renaming can slow down type lookup at runtime. If you have legacy code that expects the default type name of the activity to be based on the lowercased namespace and the class name, see Android Callable Wrapper Naming for tips on maintaining compatibility.

Activity Title Bar

By default, Android gives your application a title bar when it is run. The value used for this is /manifest/application/activity/@android:label. In most cases, this value will differ from your class name. To specify your app's label on the title bar, use the Label property. For example:

[Activity (Label="Awesome Demo App")]
public class MyActivity : Activity
{
}

This example produces the following xml fragment:

<activity android:label="Awesome Demo App" 
          android:name="md5a7a3c803e481ad8926683588c7e9031b.MainActivity" />

Launchable from Application Chooser

By default, your activity will not show up in Android's application launcher screen. This is because there will likely be many activities in your application, and you don't want an icon for every one. To specify which one should be launchable from the application launcher, use the MainLauncher property. For example:

[Activity (Label="Awesome Demo App", MainLauncher=true)] 
public class MyActivity : Activity
{
}

This example produces the following xml fragment:

<activity android:label="Awesome Demo App" 
          android:name="md5a7a3c803e481ad8926683588c7e9031b.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

Activity Icon

By default, your activity will be given the default launcher icon provided by the system. To use a custom icon, first add your .png to Resources/drawable, set its Build Action to AndroidResource, then use the Icon property to specify the icon to use. For example:

[Activity (Label="Awesome Demo App", MainLauncher=true, Icon="@drawable/myicon")] 
public class MyActivity : Activity
{
}

This example produces the following xml fragment:

<activity android:icon="@drawable/myicon" android:label="Awesome Demo App" 
          android:name="md5a7a3c803e481ad8926683588c7e9031b.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

Permissions

When you add permissions to the Android Manifest (as described in Add Permissions to Android Manifest), these permissions are recorded in Properties/AndroidManifest.xml. For example, if you set the INTERNET permission, the following element is added to Properties/AndroidManifest.xml:

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

Debug builds automatically set some permissions to make debug easier (such as INTERNET and READ_EXTERNAL_STORAGE) – these settings are set only in the generated obj/Debug/android/AndroidManifest.xml and are not shown as enabled in the Required permissions settings.

For example, if you examine the generated manifest file at obj/Debug/android/AndroidManifest.xml, you may see the following added permission elements:

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

In the Release build version of the manifest (at obj/Debug/android/AndroidManifest.xml), these permissions are not automatically configured. If you find that switching to a Release build causes your app to lose a permission that was available in the Debug build, verify that you have explicitly set this permission in the Required permissions settings for your app (see Build > Android Application in Visual Studio for Mac; see Properties > Android Manifest in Visual Studio).

Advanced Features

Intent Actions and Features

The Android manifest provides a way for you to describe the capabilities of your activity. This is done via Intents and the [IntentFilter] custom attribute. You can specify which actions are appropriate for your activity with the IntentFilter constructor, and which categories are appropriate with the Categories property. At least one activity must be provided (which is why activities are provided in the constructor). [IntentFilter] can be provided multiple times, and each use results in a separate <intent-filter/> element within the <activity/>. For example:

[Activity (Label="Awesome Demo App", MainLauncher=true, Icon="@drawable/myicon")] 
[IntentFilter (new[]{Intent.ActionView}, 
        Categories=new[]{Intent.CategorySampleCode, "my.custom.category"})]
public class MyActivity : Activity
{
}

This example produces the following xml fragment:

<activity android:icon="@drawable/myicon" android:label="Awesome Demo App" 
          android:name="md5a7a3c803e481ad8926683588c7e9031b.MainActivity">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
  <intent-filter>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.SAMPLE_CODE" />
    <category android:name="my.custom.category" />
  </intent-filter>
</activity>

Application Element

The Android manifest also provides a way for you to declare properties for your entire application. This is done via the <application> element and its counterpart, the Application custom attribute. Note that these are application-wide (assembly-wide) settings rather than per-Activity settings. Typically, you declare <application> properties for your entire application and then override these settings (as needed) on a per-Activity basis.

For example, the following Application attribute is added to AssemblyInfo.cs to indicate that the application can be debugged, that its user-readable name is My App, and that it uses the Theme.Light style as the default theme for all activities:

[assembly: Application (Debuggable=true,   
                        Label="My App",   
                        Theme="@android:style/Theme.Light")]

This declaration causes the following XML fragment to be generated in obj/Debug/android/AndroidManifest.xml:

<application android:label="My App" 
             android:debuggable="true" 
             android:theme="@android:style/Theme.Light"
                ... />

In this example, all activities in the app will default to the Theme.Light style. If you set an Activity's theme to Theme.Dialog, only that Activity will use the Theme.Dialog style while all other activities in your app will default to the Theme.Light style as set in the <application> element.

The Application element is not the only way to configure <application> attributes. Alternately, you can insert attributes directly into the <application> element of Properties/AndroidManifest.xml. These settings are merged into the final <application> element that resides in obj/Debug/android/AndroidManifest.xml. Note that the contents of Properties/AndroidManifest.xml always override data provided by custom attributes.

There are many application-wide attributes that you can configure in the <application> element; for more information about these settings, see the Public Properties section of ApplicationAttribute.

List of Custom Attributes