AsyncTask safe stop

MainActivity.java

/*
在使用 AsyncTask 停止常常被人忽略的問題以下兩種。

1. 呼叫了 cancel() 但是沒有馬上停止而造成其他 crash。
2. Activity 已經被 onDestory 但是 AsyncTask 沒有被 cancel 造成 crash。
*/

public class MainActivity extends Activity {

	private final static String TAG = "MainActivity";
	private AsyncTask<Void, Void, Boolean> async;
	private Handler handler = new Handler();

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		async = new AsyncTask<Void, Void, Boolean>() {
		
			@Override
			protected void onPreExecute() {
				super.onPreExecute();
				Log.d(TAG, "onPreExecute()");
			}
			
			@Override
			protected Boolean doInBackground(Void... params) {
				try {
					for (int i = 0; i< 10; i++) {
						Log.d(TAG, "i = " + i);
						Thread.sleep(1000);
					}
				} catch (InterruptedException e) {
					e.printStackTrace();
					Log.e(TAG, "InterruptedException");
				}
				return true;
			}
			
			@Override
			protected void onCancelled() {
				super.onCancelled();
				Log.d(TAG, "onCancelled()");
			}
			
			@Override
			protected void onCancelled(Boolean result) {
				super.onCancelled(result);
				Log.d(TAG, "onCancelled(result): " + String.valueOf(result));
			}
			
			
			@Override
			protected void onPostExecute(Boolean result) {
				super.onPostExecute(result);  //  不使用就不會呼叫 protected void onCancelled()
				Log.d(TAG, "onPostExecute");
			}
		
		}.execute();
		
		handler.postDelayed(new Runnable() {
			
			@Override
			public void run() {
				async.cancel(true); //  立即中止會引發 InterruptedException
			}
		}, 1000 * 3);
	}
}

/*
[Log display]

onCancelled()
onCancelled(result): true

[Readme]
1. 可以在 doInBackground() 做 isCancelled() 檢查，提早做結束


[Ref]
http://www.cnblogs.com/wangfenjin/archive/2012/09/21/2696905.html
http://blog.csdn.net/snow4dev/article/details/8809897
*/