java - 在Android的AsyncTask的onPostExecute上显示alertDialog

我有一个asyncTask，并且我想在触发alertDialog方法时显示一个onPostExecute。
我声明了一个Context变量，并在OnCreate方法中将其初始化为：

mContext = this;

然后为了在onPostExecute方法上显示alertDialog，我使用了以下代码：

            AlertDialog.Builder goLogin = new AlertDialog.Builder(mContext);
            goLogin.setMessage("test");
            goLogin.setCancelable(false);
            goLogin.setPositiveButton("ok",
                    new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();
                }
            });
        AlertDialog alertLogin = goLogin.create();
        alertLogin.show();

但是我得到的是以下错误：

07-10 14:42:09.710: E/AndroidRuntime(12963): java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:148)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:99)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:154)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.app.AlertDialog$Builder.<init>(AlertDialog.java:379)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at test.test.showAlert(test.java:671)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at test.test.checkResult(test.java:656)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at test.test$login.onPostExecute(test.java:585)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at test.test$login.onPostExecute(test.java:1)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.os.AsyncTask.finish(AsyncTask.java:632)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.os.Handler.dispatchMessage(Handler.java:102)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.os.Looper.loop(Looper.java:135)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at android.app.ActivityThread.main(ActivityThread.java:5312)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at java.lang.reflect.Method.invoke(Native Method)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at java.lang.reflect.Method.invoke(Method.java:372)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
07-10 14:42:09.710: E/AndroidRuntime(12963):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

我究竟做错了什么？我是否需要以其他方式传递上下文？

编辑：
整个AsyncTask代码：

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


@Override
protected void onPreExecute() {
    super.onPreExecute();
    // Showing progress dialog

}

@SuppressWarnings("deprecation")
@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("userName", "test"));
    String jsonStr = sh.makeServiceCall(urlTest, ServiceHandler.POST, params);


    if (jsonStr != null) {
        try {

            JSONObject obj = new JSONObject(jsonStr);

            error = obj.getBoolean("Error");
            if(!error)
            {
                loginResult = true;
                JSONObject array = obj.getJSONObject("Response");
                name = array.getString("Name");
            }
            else
            {
                loginResult = 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(context);
    reorder.setMessage("error");
    reorder.setCancelable(true);
    reorder.setPositiveButton("ok",
            new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            dialog.dismiss();
        }
    });

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

}

最佳答案

创建AsyncTask的构造函数，然后执行以下操作：

private class DemoTask extends AsyncTask<Void, Void, Void> {
         Context context;

    public DemoTask(Context mContext) {
        this.context = mContext;
    }

        @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);

            AlertDialog.Builder goLogin = new AlertDialog.Builder(context);
            goLogin.setMessage("test");
            goLogin.setCancelable(false);
            goLogin.setPositiveButton("ok", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();
                }
            });
            AlertDialog alertLogin = goLogin.create();
            alertLogin.show();
        }

    }

这里mContext在onCreate方法内部：

public class MyActivity extends Activity {

private Context mContext;


@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mContext = this;

        new DemoTask(mContext).execute();
    }

关于java - 在Android的AsyncTask的onPostExecute上显示alertDialog，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/31340732/