On Java Android API how to start a virtual display and use Accessibility `takeScreenshot` over it?
Mar 13, 5:54pm

To start a virtual display and use the AccessibilityService's takeScreenshot method over it in Android, you need to combine the MediaProjection API (for virtual display creation) and the AccessibilityService API (for taking screenshots). Here’s a step-by-step guide:

1. Declare Permissions

In your AndroidManifest.xml, declare the necessary permissions:

xml
<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" /> <!-- Optional, if needed -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> <!-- If saving screenshots -->

2. Create a Virtual Display

Use MediaProjectionManager to create a virtual display. You need user permission to capture the screen.

a. Request Screen Capture Permission

java
MediaProjectionManager mProjectionManager =
    (MediaProjectionManager) getSystemService(Context.MEDIA_PROJECTION_SERVICE);
Intent permissionIntent = mProjectionManager.createScreenCaptureIntent();
startActivityForResult(permissionIntent, REQUEST_CODE);

b. Create Virtual Display

After getting permission, create a virtual display:

java
MediaProjection mMediaProjection = mProjectionManager.getMediaProjection(resultCode, data);
DisplayMetrics metrics = getResources().getDisplayMetrics();
int width = metrics.widthPixels;
int height = metrics.heightPixels;
int dpi = metrics.densityDpi;

ImageReader mImageReader = ImageReader.newInstance(width, height, PixelFormat.RGBA_8888, 2);
VirtualDisplay mVirtualDisplay = mMediaProjection.createVirtualDisplay(
    "ScreenCapture",
    width, height, dpi,
    DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR,
    mImageReader.getSurface(), null, null);

3. Use AccessibilityService to Take Screenshot

Extend AccessibilityService and use takeScreenshot (API 30+).

a. Declare Accessibility Service in Manifest

xml
<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>

b. Create accessibility_service_config.xml

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

c. Implement takeScreenshot

java
public class MyAccessibilityService extends AccessibilityService {
    @Override
    public void onAccessibilityEvent(AccessibilityEvent event) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
            takeScreenshot(
                /* displayId */ Display.DEFAULT_DISPLAY,
                /* exec */ new ScreenshotCallback() {
                    @Override
                    public void onSuccess(ScreenshotResult result) {
                        // Handle screenshot result
                    }
                    @Override
                    public void onFailure(int errorCode) {
                        // Handle error
                    }
                });
        }
    }
    @Override
    public void onInterrupt() {}
}

4. Combine Virtual Display and Screenshot

  • The virtual display mirrors the main screen.
  • Use AccessibilityService.takeScreenshot on the virtual display’s ID (if supported) or the default display.

5. Clean Up

Release resources when done:

java
mVirtualDisplay.release();
mMediaProjection.stop();

Key Notes

  • API Level: takeScreenshot requires API 30 (Android 11).
  • User Consent: Both MediaProjection and AccessibilityService require explicit user consent.
  • Testing: Test on a real device, as emulators may not support virtual displays or screenshots.
Mar 13, 5:54pm

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