Question

我要做的是使用异步任务在我的应用搜索其位置时显示进度对话框。找到它们的位置后，它应显示一个包含一些信息的警告对话框。但我不是百分百肯定如何做到这一点。这就是我在LocationChanged.java中所拥有的：

@Override
protected Void doInBackground( Void... params ) {
    final LocationManager locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
    geocoder = new Geocoder(context, Locale.getDefault());
    final LocationListener locationListener = new LocationListener() {
        public void onLocationChanged(Location location) {
            // Called when a new location is found by the network location provider.
            lat =location.getLatitude();
            lon = location.getLongitude();
            //TextView tv = (TextView) findViewById(R.id.tv3);
            try{
                addresses=(geocoder.getFromLocation(lat, lon, 1));
                if (addresses.size() > 0) {
                    // String address = addresses.get(0).getAddressLine(0);
                    String city = addresses.get(0).getAddressLine(1);
                    String id = city.substring(0,city.length()-5);
                    String state1=String.valueOf(id.charAt(id.length()-3));
                    String state2=String.valueOf(id.charAt(id.length()-2));
                    STATE = state1+state2;
                    //String country = addresses.get(0).getAddressLine(2);
                    //tv.setText(STATE);
                    progressDialog.dismiss();
                    locationManager.removeUpdates(this);
                }
                else {
                    //tv.setText("Oops...");
                }

            }catch(IOException e){
                e.printStackTrace();
            }

        }

这是运行时的logcat：

07-08 17:26:21.456: ERROR/AndroidRuntime(2755): FATAL EXCEPTION: AsyncTask #1
    java.lang.RuntimeException: An error occured while executing doInBackground()
    at android.os.AsyncTask$3.done(AsyncTask.java:299)
    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
    at java.lang.Thread.run(Thread.java:864)
    Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
    at android.os.Handler.<init>(Handler.java:121)
    at android.location.LocationManager$ListenerTransport$1.<init>(LocationManager.java:209)
    at android.location.LocationManager$ListenerTransport.<init>(LocationManager.java:209)
    at android.location.LocationManager._requestLocationUpdates(LocationManager.java:687)
    at android.location.LocationManager.requestLocationUpdates(LocationManager.java:512)
    at com.nick.whatsthetip.LocationChanged.doInBackground(LocationChanged.java:121)
    at com.nick.whatsthetip.LocationChanged.doInBackground(LocationChanged.java:24)
    at android.os.AsyncTask$2.call(AsyncTask.java:287)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
    ... 5 more
07-08 17:26:21.716: ERROR/EmbeddedLogger(696): App crashed! Process:    com.nick.whatsthetip
07-08 17:26:21.716: ERROR/EmbeddedLogger(696): App crashed! Package: com.nick.whatsthetip v5 (1.1.0)
07-08 17:26:21.987: ERROR/WindowManager(2755): Activity com.nick.whatsthetip.Settings    has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@41075198 that was originally added here
    android.view.WindowLeaked: Activity com.nick.whatsthetip.Settings has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@41075198 that was originally added here
    at android.view.ViewRootImpl.<init>(ViewRootImpl.java:468)
    at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:419)
    at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:351)
    at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:171)
    at android.view.Window$LocalWindowManager.addView(Window.java:558)
    at android.app.Dialog.show(Dialog.java:282)
    at android.app.ProgressDialog.show(ProgressDialog.java:116)
    at android.app.ProgressDialog.show(ProgressDialog.java:99)
    at android.app.ProgressDialog.show(ProgressDialog.java:94)
    at com.nick.whatsthetip.LocationChanged.onPreExecute(LocationChanged.java:49)
    at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
    at android.os.AsyncTask.execute(AsyncTask.java:534)
    at com.nick.whatsthetip.Settings$3.onClick(Settings.java:119)
    at android.view.View.performClick(View.java:4102)

Answer 1

您应该知道，AsyncTask的doInBackground方法是在“Worker”线程上执行的，只有onProgressUpdate和onPostExecute在主线程上执行，因此，尝试修改与UI相关的任何内容（如进度对话框.. 。）来自doInBackground将导致异常，您需要做的是确保修改UI的任何代码都是从主线程调用而不是从工作线程调用...

此致

Answer 2

此培训课程：Displaying a Location Address向您展示如何运行AsyncTask以反转地理位置。

没有必要在后台响应位置更新。我建议你从doInBackground中取出onLocationChanged并将其作为UI线程中的方法添加。它是异步的，因此不会导致ANR。获得位置后，然后执行查找城市，州等的后台任务。培训课程将向您展示如何在不使用对话框的情况下建立进度指示器。

具有异步任务问题的进度对话框

2 个答案: