Android MediaProjection内存泄漏求助：复现步骤与规避方法？

问题概述 #

MediaProjection在启动并停止后，会出现内存泄漏问题，导致关联的Service无法被GC回收，LeakCanary可检测到该泄漏。泄漏链路为：Native全局变量 → MediaProjectionCallback → MediaProjection → Context → Service

复现步骤 #

• 遵循Android官方MediaProjection使用指引，完成启动、停止MediaProjection的流程即可复现。
• 核心操作步骤：
  1. 请求屏幕捕获权限：

     startActivityForResult(
         mediaProjectionManager.createScreenCaptureIntent(),
         REQUEST_CODE
     )
     

     （代码位于Demo的MainActivity类中）
  2. 初始化MediaProjection：

     mediaProjection = mediaProjectionManager.getMediaProjection(
         intent.getIntExtra("RESULT_CODE", 0),
         intent.getParcelableExtra<Intent>("DATA")!!
     )
     

     （代码位于Demo的ScreenCaptureService类中）

泄漏追踪信息 #

LeakCanary检测到的泄漏日志如下：

References underlined with "~~~" are likely causes.
Learn more at https://squ.re/leaks.

625 bytes retained by leaking objects
Displaying only 1 leak trace out of 5 with the same signature
Signature: a986e3ada7a0f3d1cc20672fc5b8f41b2c2189be
┬───
│ GC Root: Global variable in native code
│
├─ android.media.projection.MediaProjection$MediaProjectionCallback instance
│    Leaking: UNKNOWN
│    Retaining 3.2 kB in 27 objects
│    ↓ MediaProjection$MediaProjectionCallback.this$0
│                                              ~~~~~~
├─ android.media.projection.MediaProjection instance
│    Leaking: UNKNOWN
│    Retaining 2.7 kB in 26 objects
│    mContext instance of android.app.ContextImpl
│    ↓ MediaProjection.mContext
│                      ~~~~~~~~
├─ android.app.ContextImpl instance
│    Leaking: UNKNOWN
│    Retaining 1.6 kB in 20 objects
│    mOuterContext instance of rpetrov.test.mediaprojectionleakdemo.ScreenCaptureService
│    ContextImpl.mOuterContext is an instance of rpetrov.test.mediaprojectionleakdemo.ScreenCaptureService
│    ↓ ContextImpl.mOuterContext
│                  ~~~~~~~~~~~~~
╰→ rpetrov.test.mediaprojectionleakdemo.ScreenCaptureService instance
​     Leaking: YES (ObjectWatcher was watching this because rpetrov.test.mediaprojectionleakdemo.ScreenCaptureService
​     received Service#onDestroy() callback and Service not held by ActivityThread)
​     Retaining 125 B in 2 objects
​     key = 68f51a96-1353-4155-b47b-4c9adeee759e
​     watchDurationMillis = 5904
​     retainedDurationMillis = 900
​     mApplication instance of android.app.Application
​     mBase instance of android.app.ContextImpl

源码分析 #

MediaProjectionManager创建MediaProjection的逻辑 #

public MediaProjection getMediaProjection(int resultCode, @NonNull Intent resultData) {
    if (resultCode != Activity.RESULT_OK || resultData == null) {
        return null;
    }
    IBinder projection = resultData.getIBinderExtra(EXTRA_MEDIA_PROJECTION);
    if (projection == null) {
        return null;
    }
    return new MediaProjection(mContext, IMediaProjection.Stub.asInterface(projection));
}

MediaProjection构造方法内部逻辑 #

public MediaProjection(Context context, IMediaProjection impl) {
    mCallbacks = new ArrayMap<Callback, CallbackRecord>();
    mContext = context;
    mImpl = impl;
    try {
        mImpl.start(new MediaProjectionCallback());
    } catch (RemoteException e) {
        throw new RuntimeException("Failed to start media projection", e);
    }
}

泄漏原因：

1. MediaProjectionCallback是MediaProjection的内部类，会持有外部类MediaProjection的强引用；
2. MediaProjection持有传入的Context实例（此处为Service的Context）；
3. MediaProjectionCallback被Native层的全局变量引用，导致整个引用链无法被GC回收，最终Service实例泄漏。

可行规避方案 #

1. 使用Application Context替代组件Context
   获取MediaProjection时，传入Application Context而非Service/Activity的Context，因为Application Context的生命周期与应用一致，不会因组件销毁导致泄漏：

   mediaProjection = mediaProjectionManager.getMediaProjection(
       resultCode,
       resultData,
       applicationContext // 替换为Application Context
   )
   

2. 主动销毁MediaProjection并置空引用
   在组件（如Service）的onDestroy方法中，主动调用MediaProjection.stop()，并将引用置空，切断引用链：

   override fun onDestroy() {
       super.onDestroy()
       mediaProjection?.stop()
       mediaProjection = null
   }
   

3. 避免长期持有MediaProjection引用
   仅在需要屏幕捕获时持有MediaProjection实例，完成操作后立即释放，减少引用持有时间。

内容的提问来源于stack exchange，提问作者Puzirki