如何在 Android AsyncTask 中显示 Toast? [英] How to display a Toast in Android AsyncTask?

问题描述

我试图在用 AsyncTask 扩展的 initial_background 类中显示 Toast.我在 logcat 中收到此错误.

I am trying to display Toast in my initial_background class extended with AsyncTask<URL, Integer, Long>. I am receiving this error in logcat.

public class InitialBackgroundTask extends AsyncTask<URL, Integer, Long> {

    @Override
    protected Long doInBackground(URL... params) {
        // TODO Auto-generated method stub
        show a = new show();
        a.loop();
        return null;
    }

public class show {

    void loop()
    {
        for(int i=0; i<10; i++)
        {
            Toast.makeText(MainActivity.me, "test", Toast.LENGTH_LONG).show();
        }
    }
}

这是个例外:

05-30 12:08:12.641: E/AndroidRuntime(30840): FATAL EXCEPTION: AsyncTask #1
05-30 12:08:12.641: E/AndroidRuntime(30840): java.lang.RuntimeException: An error occured while executing doInBackground()
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.os.AsyncTask$3.done(AsyncTask.java:278)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.lang.Thread.run(Thread.java:856)
05-30 12:08:12.641: E/AndroidRuntime(30840): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.os.Handler.<init>(Handler.java:121)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.widget.Toast$TN.<init>(Toast.java:317)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.widget.Toast.<init>(Toast.java:91)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.widget.Toast.makeText(Toast.java:233)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at   com.example.toast.show.loop(show.java:11)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at com.example.toast.InitialBackgroundTask.doInBackground(InitialBackgroundTask.java:13)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at com.example.toast.InitialBackgroundTask.doInBackground(InitialBackgroundTask.java:1)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at android.os.AsyncTask$2.call(AsyncTask.java:264)
05-30 12:08:12.641: E/AndroidRuntime(30840):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
05-30 12:08:12.641: E/AndroidRuntime(30840):    ... 5 more

上面的代码展示了整个故事.其实我想在doInBackground方法中显示toast

The above code is showing the whole story. Actually, I want to show toast in doInBackground method

推荐答案

您无法在后台线程上更新 UI.doInBackground() 在后台线程上调用.您应该在 UI 线程上更新 UI.

You cannot update UI on background thread. doInBackground() is invoked on the background thread. You should update UI on the UI thread.

      runOnUiThread(new Runnable(){

          @Override
          public void run(){
            //update ui here
            // display toast here 
          }
       });

onPreExecute()、onPostExecute(Result) 在 UI 线程上调用.所以你可以在这里展示吐司.

onPreExecute(), onPostExecute(Result), are invoked on the UI thread. So you can display toast here.

onProgressUpdate(Progress...)，在调用 publishProgress(Progress...) 后在 UI 线程上调用，可用于动画进度条或在文本字段中显示日志.

onProgressUpdate(Progress...), invoked on the UI thread after a call to publishProgress(Progress...) can be used to animate a progress bar or show logs in a text field.

doInBackground() 计算的结果是 onPostExecute(Result) 的参数，因此在 doinBackground() 中返回结果并显示您的onPostExecute(Result)

The result of doInBackground() computation is a parameter to onPostExecute(Result) so return the result in doinBackground() and show your toast in onPostExecute(Result)

您也可以按照@Stine Pike 的建议使用处理程序

You can also use a handler as suggested by @Stine Pike

为清楚起见，请查看主题下的以下链接:4 个步骤.

For clarity, check the link below under the topic: The 4 steps.

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

这篇关于如何在 Android AsyncTask 中显示 Toast?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！