How to use a static inner AsyncTask class

为了防止泄漏，可以将内部类设置为静态.但问题是，您不再有权访问活动的UI视图或成员变量.您可以传入对Context的引用，但随后您将面临同样的内存泄漏风险.(如果AsyncTask类对活动有强引用，则Android无法在活动关闭后对其进行垃圾收集.)解决方法是对活动进行弱引用(或任何你需要的Context).

public class MyActivity extends AppCompatActivity {

    int mSomeMemberVariable = 123;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // start the AsyncTask, passing the Activity context
        // in to a custom constructor 
        new MyTask(this).execute();
    }

    private static class MyTask extends AsyncTask<Void, Void, String> {

        private WeakReference<MyActivity> activityReference;

        // only retain a weak reference to the activity 
        MyTask(MyActivity context) {
            activityReference = new WeakReference<>(context);
        }

        @Override
        protected String doInBackground(Void... params) {

            // do some long running task...

            return "task finished";
        }

        @Override
        protected void onPostExecute(String result) {

            // get a reference to the activity if it is still there
            MyActivity activity = activityReference.get();
            if (activity == null || activity.isFinishing()) return;

            // modify the activity's UI
            TextView textView = activity.findViewById(R.id.textview);
            textView.setText(result);

            // access Activity member variables
            activity.mSomeMemberVariable = 321;
        }
    }
}

Notes

• 据我所知，这种内存泄漏的危险一直是真实的，但我只是在Android Studio 3.0中才开始看到警告.有很多主要的AsyncTask个教程仍然没有涉及到这一点(参见here、here、here和here).
• 如果你的AsyncTask名学生是顶级学生，你也会遵循类似的程序.静态内部类基本上与Java中的顶级类相同.

• 如果您不需要活动本身，但仍然需要上下文(例如，显示Toast)，则可以传入对应用程序上下文的引用.在本例中，AsyncTask构造函数将如下所示:

  private WeakReference<Application> appReference;
  
  MyTask(Application context) {
      appReference = new WeakReference<>(context);
  }
  

• 有一些理由认为应该忽略这个警告，只使用非静电类.毕竟，AsyncTask的目的是非常短暂的(最长几秒钟)，而且无论如何它都会在完成时释放对该活动的引用.请参见this和this.
• 优秀文章:How to Leak a Context: Handlers & Inner Classes篇

Kotlin

在Kotlin ，内部阶级只有don't include the inner keyword人.这使得它在默认情况下是静态的.

class MyActivity : AppCompatActivity() {

    internal var mSomeMemberVariable = 123

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // start the AsyncTask, passing the Activity context
        // in to a custom constructor
        MyTask(this).execute()
    }

    private class MyTask
    internal constructor(context: MyActivity) : AsyncTask<Void, Void, String>() {

        private val activityReference: WeakReference<MyActivity> = WeakReference(context)

        override fun doInBackground(vararg params: Void): String {

            // do some long running task...

            return "task finished"
        }

        override fun onPostExecute(result: String) {

            // get a reference to the activity if it is still there
            val activity = activityReference.get()
            if (activity == null || activity.isFinishing) return

            // modify the activity's UI
            val textView = activity.findViewById(R.id.textview)
            textView.setText(result)

            // access Activity member variables
            activity.mSomeMemberVariable = 321
        }
    }
}