无法在AsyncTask的onPostExecute方法上显示Toast或AlertDialog

Question

I'm struggling with this error since 2 days now and I can't figure out how to fix it. I have an order method for a product that calls a webservice, I parse the response and if the response is negative I have to show an AlertDialog inside the onPostExecute method. This is the code i'm using:

private class test extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
        @Override
        protected Void doInBackground(Void... arg0) {
            // Creating service handler class instance
            ServiceHandler sh = new ServiceHandler();

            // Making a request to url and getting response
            List<NameValuePair> params = new ArrayList<NameValuePair>();


            params.add(new BasicNameValuePair("deviceOS", "Android"));
            String jsonStr = sh.makeServiceCall(urlTest, ServiceHandler.POST, params);


            if (jsonStr != null) {
                try {

                    JSONObject obj = new JSONObject(jsonStr);

                    error = obj.getBoolean("Error");
                    if(!error)
                    {
                        test = true;
                        JSONObject array = obj.getJSONObject("Response");

                        token = array.getString("Token");

                    }
                    else
                    {
                        test = false;
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                }
            } else {

            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            //checkResult();
            AlertDialog.Builder reorder = new AlertDialog.Builder(myActivity.this);
            reorder.setMessage("test");
            reorder.setCancelable(true);
            reorder.setPositiveButton("ok",
                    new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    dialog.dismiss();
                }
            });

            AlertDialog orderError = reorder.create();
            orderError.show();
        }

    }

When the app reaches the onPostExecute method it crashes and the log is this:

07-13 11:58:31.074: E/AndroidRuntime(2529): FATAL EXCEPTION: main
07-13 11:58:31.074: E/AndroidRuntime(2529): Process: com.test.Test, PID: 2529
07-13 11:58:31.074: E/AndroidRuntime(2529): java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:148)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:99)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:154)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.app.AlertDialog$Builder.<init>(AlertDialog.java:379)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at test.test$login.onPostExecute(test.java:575)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at test.test$test.onPostExecute(test.java:1)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.os.AsyncTask.finish(AsyncTask.java:632)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.os.Handler.dispatchMessage(Handler.java:102)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.os.Looper.loop(Looper.java:135)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at android.app.ActivityThread.main(ActivityThread.java:5312)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at java.lang.reflect.Method.invoke(Native Method)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at java.lang.reflect.Method.invoke(Method.java:372)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
07-13 11:58:31.074: E/AndroidRuntime(2529):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

Does anyone know what the error could be?

Answer 1

Why are you create 2 times AlertDialog? Using Builder you can show it. Change Below code and Works fine. Replace

AlertDialog.Builder reorder = new AlertDialog.Builder(myActivity.this);

with

AlertDialog.Builder reorder = new AlertDialog.Builder(myActivity.this).create();

and
Remove

AlertDialog orderError = reorder.create();
orderError.show();

and add

reorder.show();

Thats it...

Answer 2

使用前，请确保已初始化“ urlTest ”。

Answer 3

Try this.

private class test extends AsyncTask<Void, Void, Void> {

    WeakReference<Activity> weakActivity;

    public test(Activity activity) {
        weakActivity = activity;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }
    @Override
    protected Void doInBackground(Void... arg0) {
        //blah blah code!
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        Activity activity = weakActivity.get();
        if (activity != null) {

            // Dismiss the progress dialog
        //checkResult();
        AlertDialog.Builder reorder = new AlertDialog.Builder(activity);
        reorder.setMessage("test");
        reorder.setCancelable(true);
        reorder.setPositiveButton("ok",
                new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.dismiss();
            }
        });

        AlertDialog orderError = reorder.create();
        orderError.show();
        }
    }

}