AsyncTask 中的 Android AlertDialog

Question

我有一个带有复选框的列表视图。对于每个复选框（大约 3 个），它都有一个特定的 AsyncTask。

我永远不知道 用户选择了什么复选框，所以我不能在异步任务的末尾放置 AlertDialog，因为我永远不知道用户是否只选择了一个复选框，还是两个或三个。

因为 AsyncTask 是分步执行的（只有当第一个 Async 完成时第二个 Async 才开始），我想在所有内容的末尾放置一个带有 AlertDialog 的新 AsyncTask。

 private class showMessageAsync extends AsyncTask<Void, Integer, String> {
    @Override
    protected String doInBackground(Void... params){
        AlertDialog alertDialog;
        alertDialog = new AlertDialog.Builder(getApplicationContext).create();
        alertDialog.setTitle("The Process");
        alertDialog.setIcon(R.drawable.success);
        alertDialog.setCanceledOnTouchOutside(false);
        alertDialog.setMessage("All done!");
        alertDialog.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
                              new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Intent A = new Intent(DownloadActivity.this, Menu_activity.class);
                startActivity(A);
                finish();
            }
        });
        alertDialog.setOnDismissListener(new DialogInterface.OnDismissListener() {
            @Override
            public void onDismiss(DialogInterface dialog) {
                Intent A = new Intent(DownloadActivity.this, Menu_activity.class);
                startActivity(A);
                finish();
            }
        });
        alertDialog.show();
        return "Executed";
    }
}

这是错误：

 10-21 04:24:34.117: E/AndroidRuntime(1026): FATAL EXCEPTION: AsyncTask
#4 10-21 04:24:34.117: E/AndroidRuntime(1026): java.lang.RuntimeException: An error occured while executing
doInBackground() 10-21 04:24:34.117: E/AndroidRuntime(1026):    at
android.os.AsyncTask$3.done(AsyncTask.java:299) 10-21 04:24:34.117:
E/AndroidRuntime(1026):     at
java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
10-21 04:24:34.117: E/AndroidRuntime(1026):     at
java.util.concurrent.FutureTask.setException(FutureTask.java:219)
10-21 04:24:34.117: E/AndroidRuntime(1026):     at
java.util.concurrent.FutureTask.run(FutureTask.java:239) 10-21
04:24:34.117: E/AndroidRuntime(1026):   at
android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 10-21
04:24:34.117: E/AndroidRuntime(1026):   at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
10-21 04:24:34.117: E/AndroidRuntime(1026):     at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
10-21 04:24:34.117: E/AndroidRuntime(1026):     at
java.lang.Thread.run(Thread.java:841) 10-21 04:24:34.117:
E/AndroidRuntime(1026): Caused by: java.lang.RuntimeException: Can't
create handler inside thread that has not called Looper.prepare()
10-21 04:24:34.117: E/AndroidRuntime(1026):     at
android.os.Handler.<init>(Handler.java:197) 10-21 04:24:34.117:
E/AndroidRuntime(1026):     at
android.os.Handler.<init>(Handler.java:111) 10-21 04:24:34.117:
E/AndroidRuntime(1026):     at android.app.Dialog.<init>(Dialog.java:107)
10-21 04:24:34.117: E/AndroidRuntime(1026):     at
android.app.AlertDialog.<init>(AlertDialog.java:114) 10-21
04:24:34.117: E/AndroidRuntime(1026):   at
android.app.AlertDialog$Builder.create(AlertDialog.java:931) 10-21
04:24:34.117: E/AndroidRuntime(1026):   at com.example.MyExample.DownloadActivity$showMessageAsync.doInBackground(DownloadActivity.java:487)
10-21 04:24:34.117: E/AndroidRuntime(1026): at com.example.MyExample.DownloadActivity$showMessageAsync.doInBackground(DownloadActivity.java:1)
10-21 04:24:34.117: E/AndroidRuntime(1026):     at android.os.AsyncTask$2.call(AsyncTask.java:287) 10-21 04:24:34.117:
E/AndroidRuntime(1026):     at java.util.concurrent.FutureTask.run(FutureTask.java:234) 10-21
04:24:34.117: E/AndroidRuntime(1026):   ... 4 more

我这样称呼我的 AsyncTask：

 if(list.get(0).isSelected() == true){
    // list = class that contains checkboxs state
    String[] params = {order, String.valueOf(limit_customers) };
    customers.execute(params);
}
if(list.get(1).isSelected() == true){
    String[] params = {order, String.valueOf(limit_products) };
    products.execute(params);
}
// etc, and in the end of this:
showMessageAsync sM = new showMessageAsync();
sM.execute();

错误在这一行：

 alertDialog = new AlertDialog.Builder(getApplicationContext()).create();

原文由 user2742861 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

警报对话框是前台的东西，所以它不能在异步任务的后台方法中完成。这样做

private class showMessageAsync extends AsyncTask<String, Void, String> {
     AlertDialog alertDialog;
     protected void onPreExecute() {
    super.onPreExecute();
            alertDialog = new AlertDialog.Builder(YourClasss.this);
     }
     @Override
     protected String doInBackground(Void... params){
            return null;
     }
     @Override
     protected void onPostExecute(String result) {
            super.onPostExecute(result);

            alertDialog.setTitle("The Process");
            alertDialog.setIcon(R.drawable.success);
            alertDialog.setCanceledOnTouchOutside(false);
            alertDialog.setMessage("All done!");
            alertDialog.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
                                  new DialogInterface.OnClickListener() {
                                        public void onClick(DialogInterface dialog, int which) {
                                                Intent A = new Intent(DownloadActivity.this, Menu_activity.class);
                                                startActivity(A);
                                                finish();
                                        }
                                    });
            alertDialog.setOnDismissListener(new DialogInterface.OnDismissListener() {
                                  @Override
                                  public void onDismiss(DialogInterface dialog) {
                                            Intent A = new Intent(DownloadActivity.this, Menu_activity.class);
                                            startActivity(A);
                                            finish();
                                  }
                    });
            alertDialog.show();
    }

}

原文由 AnAndroid 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

Caused by: java.lang.RuntimeException: 无法在未调用 Looper.prepare() 的线程内创建处理程序

您正在尝试在 doInbackground 中显示一个 lertdialog。 doInbackground 在后台线程上调用。并且 ui 应该在 ui 线程上更新。

您可以在 --- 中返回后台计算结果，并在 onPostExecute doInbackground 中更新 ui。或者使用 runOnUiThread 这是活动类的一种方法。或在 onProgressUpdate(Progress...) 中显示对话框

http://developer.android.com/reference/android/os/AsyncTask.html

还要检查 Threads @ http://developer.android.com/guide/components/processes-and-threads.html 下的主题

启动应用程序时，系统会为该应用程序创建一个执行线程，称为“main”。这个线程非常重要，因为它负责将事件分派给适当的用户界面小部件，包括绘图事件。它也是您的应用程序与来自 Android UI 工具包的组件（来自 android.widget 和 android.view 包的组件）进行交互的线程。因此，主线程有时也称为 UI 线程。

还使用活动上下文

  alertDialog = new AlertDialog.Builder(ActivityContext).create();

原文由 Raghunandan 发布，翻译遵循 CC BY-SA 3.0 许可协议