Android平台下如何获取包含Dialog与Toast在内全部界面元素的像素位图？

Great question! You’re totally right that PixelCopy and Canvas-based screenshot methods only capture your Activity’s DecorView—they completely miss floating elements like Toasts, AlertDialogs, or even system overlays like the status bar. To grab a full, true-to-visual screenshot of everything visible on the screen, the official (and reliable) approach is to use the MediaProjection API, introduced in Android 5.0 (API level 21).

How It Works #

The MediaProjection API lets your app request permission to capture the entire screen, including all system and app-level overlays. Here’s a step-by-step breakdown:

1. Request Screen Capture Permission
   First, you need to ask the user for explicit permission to capture the screen via a system dialog.

   private val REQUEST_CODE_SCREEN_CAPTURE = 100
   
   fun startScreenCaptureFlow() {
       val mediaProjectionManager = getSystemService(MEDIA_PROJECTION_SERVICE) as MediaProjectionManager
       val captureIntent = mediaProjectionManager.createScreenCaptureIntent()
       startActivityForResult(captureIntent, REQUEST_CODE_SCREEN_CAPTURE)
   }
   
   override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
       super.onActivityResult(requestCode, resultCode, data)
       if (requestCode == REQUEST_CODE_SCREEN_CAPTURE && resultCode == RESULT_OK) {
           // Permission granted, proceed to capture the screen
           captureFullScreen(data!!)
       }
   }
   

2. Capture the Full Screen
   Once permission is granted, create a VirtualDisplay that mirrors the screen, then use an ImageReader to capture frame data and convert it to a Bitmap.

   private fun captureFullScreen(permissionData: Intent) {
       val mediaProjectionManager = getSystemService(MEDIA_PROJECTION_SERVICE) as MediaProjectionManager
       val mediaProjection = mediaProjectionManager.getMediaProjection(RESULT_OK, permissionData)
   
       val displayMetrics = resources.displayMetrics
       val screenWidth = displayMetrics.widthPixels
       val screenHeight = displayMetrics.heightPixels
   
       val imageReader = ImageReader.newInstance(screenWidth, screenHeight, ImageFormat.RGB_565, 1)
   
       val virtualDisplay = mediaProjection.createVirtualDisplay(
           "FullScreenCapture",
           screenWidth,
           screenHeight,
           displayMetrics.densityDpi,
           DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR,
           imageReader.surface,
           null,
           null
       )
   
       // Wait a short time for the display to stabilize before capturing
       Handler(Looper.getMainLooper()).postDelayed({
           val image = imageReader.acquireLatestImage()
           image?.let {
               val planes = it.planes
               val buffer = planes[0].buffer
               val pixelStride = planes[0].pixelStride
               val rowStride = planes[0].rowStride
               val rowPadding = rowStride - pixelStride * screenWidth
   
               // Generate the full-screen bitmap
               val fullScreenBitmap = Bitmap.createBitmap(
                   screenWidth + rowPadding / pixelStride,
                   screenHeight,
                   Bitmap.Config.RGB_565
               )
               fullScreenBitmap.copyPixelsFromBuffer(buffer)
   
               // Now you have the complete screen bitmap (Toasts, Dialogs included!)
               // Use it as needed: save to file, display in a View, etc.
   
               image.close()
               mediaProjection.stop()
               virtualDisplay.release()
           }
       }, 500)
   }
   

Key Considerations #

• Permission Durability: The MediaProjection permission is temporary—you’ll need to re-request it if the app restarts or the device reboots.
• Foreground Requirement: On Android 10 (API 29) and later, your app must be running in the foreground (with a visible activity or foreground service) to use this API.
• Performance: Screen captures are resource-heavy, so avoid frequent captures if possible to prevent lag.
• Root Workarounds: While rooted devices let you read directly from the system framebuffer, this is highly unportable and not recommended for production apps.

MediaProjection is the only official, non-root way to capture every visible element on the screen—including Toasts, Dialogs, and system UI. It’s the standard approach used by most screen recording and screenshot apps on the Play Store.

内容的提问来源于stack exchange，提问作者jay