警告：此AsyncTask类应该是静态的，否则可能发生泄漏

Question

这是我的代码：

 new AsyncTask<Void,Void,Void>(){

        @Override
        protected Void doInBackground(Void... params) {
            runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    mAdapter.notifyDataSetChanged();
                }
            });

            return null;
        }
    }.execute();

我怎么纠正这个？

Answer 1

为了防止泄漏，可以使内部类保持静态。但是，这样做的问题是，您不再能够访问活动的UI视图或成员变量。您可以传入对上下文的引用，但这样做也会面临内存泄漏的风险。（如果AsyncTask类对活动有很强的引用，Android就不能在活动关闭后对其进行垃圾回收。）解决方案是对活动（或您需要的任何上下文)进行弱引用。

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;
        }
    }
}

>

据我所知，这种类型的内存泄漏危险一直是真的，但我只是在Android Studio3.0中才开始看到警告。许多主要的AsyncTask教程仍然没有涉及它（请参阅这里、这里、这里和这里）。

如果AsyncTask是顶级类，也可以遵循类似的过程。静态内部类与Java中的顶级类基本相同。

如果不需要活动本身，但仍然需要上下文（例如，要显示toast)，可以传入对应用程序上下文的引用。在本例中，AsyncTask构造函数如下所示：

private WeakReference<Application> appReference;

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

在Kotlin中，不要包含内部类的inner关键字。这使得默认情况下它是静态的。

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
        }
    }
}