AsyncTask里面的Android AlertDialog

Question

我有一个列表视图,其中包含复选框.对于每个复选框(它们大约为3),它具有特定的AsyncTask.

我永远不知道用户选择什么样的复选框,所以我不能将异步任务放在AlertDialog的末尾,因为我永远不知道用户是否只选择了一个复选框,或者两个或三个.

因为AsyncTask是按步骤执行的(仅当第一个Async完成时才是第二个开始),我想到了一个新的AsyncTask与AlertDialog的结尾.

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

我用这种方式调用我的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();

Answer 1

警报对话框是前台事物,因此无法在异步任务的后台方法中完成.通过这种方式做到这一点

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();
    }

}