Question

我正在尝试在Android中使用AlertDialog，它会在检查互联网连接后通知用户他们正在离线模式下运行。

我使用了以下代码：

protected Void doInBackground(Void... params) {
            if (this.isOnline()) {
                    new GetJson().execute();
            } else {

        AlertDialog.Builder builder1 = new AlertDialog.Builder(homeFragment);
        builder1.setMessage("INTERNET CONNECTION NOT AVAILABLE. Now you are viewing the news in Offline Mode.");
        builder1.setCancelable(true);

        AlertDialog alert1 = builder1.create();
        alert1.show();

        try {
            saveFile = new SaveIntoFile(fileName);
            jsonStr = saveFile.read();
            // Log.d(TAG,"offline data reading from a file");
            if (!jsonStr.equals(null))
                new GetDatas().execute();
            else {

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

        }
    }
    return null;

}

但是我在添加AlertDialog的代码时收到错误。该应用程序工作正常，没有AlertDialog的代码。这段代码的错误是什么？我如何纠正它才能正常工作？

Answer 1

doInBackground（）在除主线程之外的单独线程上运行。您只能在主线程上使用UI元素。尝试在doInBackground（）中使用runOnUiThread（）方法来显示对话框。

Answer 2

这里AlertDialog不起作用，你可以使用 System.out.println（“some text”）; 如果您仅使用警报进行测试。否则你必须设置一个参数以及你想要放入alertbox的文本，只需在主线程中使用它。

如果您有任何疑惑，请告诉我。

Answer 3

在Android中，您只能在主线程中执行UI操作。因此，您可以在onPostExecute方法中显示对话框。例如：

    class anyClassName extends AsyncTask<String,String,String>{

    /* uses worker thread */
    protected String doInBackground(Void... params) {
                if (this.isOnline()) {
                        new GetJson().execute();
                } else { return null }
// ... rest of your code
return ""
    }

    /* uses main thread*/
    protected void onPostExecute(String result){
    if(result == null ){
    AlertDialog.Builder builder1 = new AlertDialog.Builder(homeFragment);
            builder1.setMessage("INTERNET CONNECTION NOT AVAILABLE. Now you are viewing the news in Offline Mode.");
            builder1.setCancelable(true);

            AlertDialog alert1 = builder1.create();
            alert1.show();
    }
    }
    }

Answer 4

 class myAsync extends AsyncTask<String, String, String>{

    @Override
    protected String doInBackground(String... arg0) {
        // TODO Auto-generated method stub          
        if(yourWorkIsDone){
            return new String("done");
        }else{
            return new String("Error message");
        }

        //BUT, if you'd like to check and update user on the error and keep trying then this way
        // use just one of these two examples
        if(yourWorkIsDone){
            // definately is done but hey it depends on you
            publishProgress(new String("done")); 
        }else{
            // this is when you have error and wona let the user know about and keep trying to hit it right
            publishProgress(new String("error message")); 
        }
    }

    @Override
    protected void onPostExecute(String result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        // here your task is done
        // you can put myAlertDialogToShow(Context context,String message) depending on ur choice
    }

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
    }

    @Override
    protected void onProgressUpdate(String... values) {
        // TODO Auto-generated method stub
        super.onProgressUpdate(values);
        // here your task is running but you are just informing user, runs on the ui..
        // you can put myAlertDialogToShow(Context context,String message) depending on ur choice
    }

}

void myAlertDialogToShow(Context context,String message){
    AlertDialog.Builder builder1 = new AlertDialog.Builder(context);
    builder1.setMessage(message);
    builder1.setCancelable(true);
    AlertDialog alert1 = builder1.create();
    alert1.show();

}

ayt..check愚蠢的错误和拼写..我很累

无法在DoInBackground中显示AlertDialog

4 个答案: