To run an Android app in a virtual display and retrieve its window UI tree using the Java Android API, you need to combine two main components:

1. Run an App in a Virtual Display

You can use the VirtualDisplay API to create a virtual display and show an app's window on it. Here’s a high-level approach:

• Create a Virtual Display:
  Use DisplayManager.createVirtualDisplay() or MediaProjection.createVirtualDisplay() to create a virtual display. You need a Surface to render the app's content onto this display.

  • Example:

    java
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    DisplayManager displayManager = (DisplayManager) context.getSystemService(Context.DISPLAY_SERVICE);
    VirtualDisplay virtualDisplay = displayManager.createVirtualDisplay(
        "MyVirtualDisplay",
        width, height, densityDpi,
        surface,
        DisplayManager.VIRTUAL_DISPLAY_FLAG_PRESENTATION
    );

• Show an App on the Virtual Display:
  Use WindowManager to add a view (like a Presentation window) to the virtual display.

  • Example:

    java
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    WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    windowManager.addView(yourView, layoutParams);

• Use MediaProjection for More Control:
  For advanced scenarios (like screen mirroring), use MediaProjection to capture the app's screen and redirect it to the virtual display.

2. Retrieve the Window UI Tree

To inspect or retrieve the UI tree of the app running on the virtual display, you can use the Accessibility API:

• Implement an Accessibility Service:
  This service can listen for UI events and provide a tree representation of the UI elements.

  • Example:

    java
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    public class MyAccessibilityService extends AccessibilityService {
        @Override
        public void onAccessibilityEvent(AccessibilityEvent event) {
            AccessibilityNodeInfo rootNode = getRootInActiveWindow();
            // Traverse the UI tree using rootNode
        }
    }

  • Register this service in your AndroidManifest.xml:

    xml
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    <service android:name=".MyAccessibilityService"
        android:permission="android.permission.BIND_ACCESSIBILITY_SERVICE">
        <intent-filter>
            <action android:name="android.accessibilityservice.AccessibilityService" />
        </intent-filter>
        <meta-data android:name="android.accessibilityservice"
            android:resource="@xml/accessibility_service_config" />
    </service>

  • Define the service config in res/xml/accessibility_service_config.xml:

    xml
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    <accessibility-service xmlns:android="http://schemas.android.com/apk/res/android"
        android:description="@string/accessibility_service_description"
        android:accessibilityEventTypes="typeAllMask"
        android:canRetrieveWindowContent="true" />

• Retrieve UI Tree:
  Use AccessibilityNodeInfo to traverse and inspect the UI elements.

Key Considerations

• Permissions: You need the android.permission.BIND_ACCESSIBILITY_SERVICE permission for the Accessibility Service.
• Virtual Display Limitations: Not all apps can be directly mirrored to a virtual display due to security restrictions.
• UI Tree Access: The Accessibility API is the standard way to inspect UI elements, but it requires the app to be in the foreground or the user to grant permissions.

Would you like a code example for a specific part of this process, or do you need help with a particular use case?