我的程序在后台线程中执行一些网络活动。在开始之前,它会弹出一个进度对话框。该对话框在处理程序上被解除。这一切都很好,除了当对话框打开时屏幕方向发生变化(背景线程正在运行)。此时,应用程序要么崩溃,要么死锁,要么进入一个奇怪的阶段,在所有线程被杀死之前,应用程序根本无法工作。

我如何处理屏幕方向的变化优雅?

下面的示例代码大致匹配我的实际程序:

public class MyAct extends Activity implements Runnable {
    public ProgressDialog mProgress;

    // UI has a button that when pressed calls send

    public void send() {
         mProgress = ProgressDialog.show(this, "Please wait", 
                      "Please wait", 
                      true, true);
        Thread thread = new Thread(this);
        thread.start();
    }

    public void run() {
        Thread.sleep(10000);
        Message msg = new Message();
        mHandler.sendMessage(msg);
    }

    private final Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            mProgress.dismiss();
        }
    };
}

栈:

E/WindowManager(  244): Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here
E/WindowManager(  244): android.view.WindowLeaked: Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here
E/WindowManager(  244):     at android.view.ViewRoot.<init>(ViewRoot.java:178)
E/WindowManager(  244):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:147)
E/WindowManager(  244):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:90)
E/WindowManager(  244):     at android.view.Window$LocalWindowManager.addView(Window.java:393)
E/WindowManager(  244):     at android.app.Dialog.show(Dialog.java:212)
E/WindowManager(  244):     at android.app.ProgressDialog.show(ProgressDialog.java:103)
E/WindowManager(  244):     at android.app.ProgressDialog.show(ProgressDialog.java:91)
E/WindowManager(  244):     at MyAct.send(MyAct.java:294)
E/WindowManager(  244):     at MyAct$4.onClick(MyAct.java:174)
E/WindowManager(  244):     at android.view.View.performClick(View.java:2129)
E/WindowManager(  244):     at android.view.View.onTouchEvent(View.java:3543)
E/WindowManager(  244):     at android.widget.TextView.onTouchEvent(TextView.java:4664)
E/WindowManager(  244):     at android.view.View.dispatchTouchEvent(View.java:3198)

我已经尝试在onSaveInstanceState中取消进度对话框,但这只是防止了立即崩溃。背景线程仍在运行,UI处于部分绘制状态。需要在它重新开始工作之前杀死整个应用程序。


当前回答

如果你维护两个布局,所有的UI线程都应该终止。

如果你使用AsynTask,那么你可以很容易地在当前活动的onDestroy()方法中调用.cancel()方法。

@Override
protected void onDestroy (){
    removeDialog(DIALOG_LOGIN_ID); // remove loading dialog
    if (loginTask != null){
        if (loginTask.getStatus() != AsyncTask.Status.FINISHED)
            loginTask.cancel(true); //cancel AsyncTask
    }
    super.onDestroy();
}

对于AsyncTask,请在“取消任务”部分阅读更多信息。

更新: 增加了检查状态的条件,因为只有当它处于运行状态时才能取消。 还要注意,AsyncTask只能执行一次。

其他回答

将长任务移动到单独的类中。将其实现为主题-观察者模式。每当创建活动时,注册并在关闭时注销任务类。任务类可以使用AsyncTask。

最简单和最灵活的解决方案是使用带有ProgressBar静态引用的AsyncTask。这为方向更改问题提供了一个封装的、因此可重用的解决方案。这个解决方案很好地帮助我完成了各种异步任务,包括互联网下载、与服务通信和文件系统扫描。该解决方案已经在多个安卓版本和手机型号上进行了良好的测试。完整的演示可以在DownloadFile.java中找到

下面是一个概念示例

public class SimpleAsync extends AsyncTask<String, Integer, String> {
    private static ProgressDialog mProgressDialog = null;
    private final Context mContext;

    public SimpleAsync(Context context) {
        mContext = context;
        if ( mProgressDialog != null ) {
            onPreExecute();
        }
    }

    @Override
    protected void onPreExecute() {
        mProgressDialog = new ProgressDialog( mContext );
        mProgressDialog.show();
    }

    @Override
    protected void onPostExecute(String result) {
        if ( mProgressDialog != null ) {
            mProgressDialog.dismiss();
            mProgressDialog = null;
        }
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        mProgressDialog.setProgress( progress[0] );
    }

    @Override
    protected String doInBackground(String... sUrl) {
        // Do some work here
        publishProgress(1);
        return null;
    }

    public void dismiss() {
        if ( mProgressDialog != null ) {
            mProgressDialog.dismiss();
        }
    }
}

在Android Activity中的使用很简单

public class MainActivity extends Activity {
    DemoServiceClient mClient = null;
    DownloadFile mDownloadFile = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.main );
        mDownloadFile = new DownloadFile( this );

        Button downloadButton = (Button) findViewById( R.id.download_file_button );
        downloadButton.setOnClickListener( new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mDownloadFile.execute( "http://www.textfiles.com/food/bakebred.txt");
            }
        });
    }

    @Override
    public void onPause() {
        super.onPause();
        mDownloadFile.dismiss();
    }
}

这是我提出的解决方案:

Move the AsyncTask or Thread to a retained Fragment, as explained here. I believe it is a good practice to move all network calls to fragments. If you are already using fragments, one of them could be made responsible for the calls. Otherwise, you can create a fragment just for doing the request, as the linked article proposes. The fragment will use a listener interface to signal the task completion/failure. You don't have to worry for orientation changes there. The fragment will always have the correct link to the current activity and progress dialog can be safely resumed. Make your progress dialog a member of your class. In fact you should do that for all dialogs. In the onPause method you should dismiss them, otherwise you will leak a window on the configuration change. The busy state should be kept by the fragment. When the fragment is attached to the activity, you can bring up the progress dialog again, if the call is still running. A void showProgressDialog() method can be added to the fragment-activity listener interface for this purpose.

看起来太“快速和肮脏”了,所以请指出缺点,但我发现有用的是……

在我的AsyncTask的onPostExecute方法中,我简单地包装了`。try/catch块中的进度对话框(带有空捕获)的Dismiss ',然后简单地忽略所引发的异常。似乎是错误的,但似乎没有不良影响(至少对于我随后所做的事情,这是启动另一个活动,将我的长时间运行查询的结果传递为一个额外)

我是一个新手在机器人,我尝试了这个,它是有效的。

public class loadTotalMemberByBranch extends AsyncTask<Void, Void,Void> {
        ProgressDialog progressDialog = new ProgressDialog(Login.this);
        int ranSucess=0;
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            progressDialog.setTitle("");    
            progressDialog.isIndeterminate();
            progressDialog.setCancelable(false);
            progressDialog.show();
            setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_NOSENSOR);

        }
        @Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub

            return null;
        }
        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            progressDialog.dismiss();
            setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_NOSENSOR);
        }
}