在AsyncTask中显示Toast

Question

  public class ayncClass extends AsyncTask<String, Void, String> {

        public void onPreExecute(){


        }
        @Override
        protected String doInBackground(String... params) {
            HttpClient client = new DefaultHttpClient();
            HttpGet get = new HttpGet(URL HERE);
            try{
                HttpResponse responseGiven = client.execute(get);
                StatusLine statusLine = responseGiven.getStatusLine();
                int statusCode = statusLine.getStatusCode();
                if(statusCode == 404){
                    Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show();

                }
            } catch(Exception e){

            }
            return null;
        }

        public void onPostExecute(...){
            super.onPostExecute(s);

        }

    }

但是，当我调试并运行该应用程序时，它确实会显示Toast。 有没有办法在AsyncTask工作时对其进行操作？

谢谢！

Answer 1

Toast属于UI。

我们只能在主线程（UI线程）中更新UI。

永远不会在主线程中调用AsyncTask.doInBackground() ，这就是原因。

Answer 2

您应该从这里使用我的代码：

public enum Toaster {
    INSTANCE;

    private final Handler handler = new Handler(Looper.getMainLooper());

    public void showToast(final Context context, final String message, final int length) {
        handler.post(
            new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(context, message, length).show();
                }
            }
        );
    }

    public static Toaster get() {
        return INSTANCE;
    }
}

那你可以做

Toaster.get().showToast(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT);

这将在UI线程上运行您的代码，并且将起作用。

Answer 3

这可能会有所帮助

onPreExecute（）{//一些代码＃1}

 doInBackground() { runOnUiThread(new Runnable() { public void run() { // some code #3 (Write your code here to run in UI thread) } }); } onPostExecute() { // some code #3 } 

Answer 4

Toast是UI元素，它不会出现，因为您的应用程序的UI在UI线程上运行，而AsyncTask doInBackground方法在不同的线程上运行。 因此，您要执行的与UI相关的任何操作都应该在onPostExecute或onPreExecute 。 如果存在这种情况，您必须在doInBackground更新UI， doInBackground可以使用处理程序线程或最佳方式，可以使用runOnUiThread方法，并且可以在其中添加吐司。

Answer 5

尝试下面

public class ayncClass extends AsyncTask<String, Void, String> {

    public void onPreExecute(){


    }
    @Override
    protected String doInBackground(String... params) {
        HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet(URL HERE);
        try{
            HttpResponse responseGiven = client.execute(get);
            StatusLine statusLine = responseGiven.getStatusLine();
            int statusCode = statusLine.getStatusCode();
            if(statusCode == 404){
                // Toast.makeText(getApplicationContext(), "ERROR", //Toast.LENGTH_SHORT).show();

            }
        } catch(Exception e){

        }
        return String.valueOf(statusCode ); // make this change
    }

    public void onPostExecute(String result){
        super.onPostExecute(s);
 Toast.makeText(getApplicationContext(), result, 
 Toast.LENGTH_SHORT).show();
    }

}

Answer 6

将Toast消息始终放置在PostExecute方法中。

公共无效onPostExecute（...）{super.onPostExecute（s;

    Toast.makeText(context, "Hellooo I am at Post Execute method", Toast.LENGTH_SHORT).show();
    }

Answer 7

只能从UI线程显示Toast 。 在UI线程中调用了onPostExecute ，因此您可以将statusCode存储在成员变量中，并在onPostExecute方法中检查404，然后在onPostExecute显示Toast 。 像这样：

public class ayncClass extends AsyncTask<String, Void, String> {

    private int mStatusCode;

    @Override
    protected String doInBackground(String... params) {
        HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet(URL HERE);
        try{
            HttpResponse responseGiven = client.execute(get);
            StatusLine statusLine = responseGiven.getStatusLine();
            mStatusCode = statusLine.getStatusCode();
        } catch(Exception e){
            // do NOT let catch blocks without log
            // if something bad happens you will never know
        }
        return null;
    }

    public void onPostExecute(...){
        super.onPostExecute(s);
        if(mStatusCode == 404){
            Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show();
        }
    }
}

或者只是将状态代码作为参数传递给onPostExecute：

public class ayncClass extends AsyncTask<String, Void, Integer> {

    @Override
    protected Integer doInBackground(String... params) {
        HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet(URL HERE);
        try{
            HttpResponse responseGiven = client.execute(get);
            StatusLine statusLine = responseGiven.getStatusLine();
            return statusLine.getStatusCode();
        } catch(Exception e){
            // do NOT let catch blocks without log
            // if something bad happens you will never know
        }
        return -1;
    }

    public void onPostExecute(Integer statusCode){
        super.onPostExecute(s);
        if(statusCode == 404){
            Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show();
        }
    }
}

Answer 8

仅当您必须向UI线程中显示某些内容（例如Toast消息）时，然后编写：

runOnUiThread(new Runnable(){
    public void run() {
        //Interaction with UI (Toast message)
    }
});

Answer 9

您无法在doInBackground函数中显示吐司，因为doInBackground函数不适用于UI线程。 您可以将进度发布到onProgressUpdate函数。 它将在UI Thread上工作。

public class ayncClass extends AsyncTask<String, Void, String> {

    private final Context context;

    public ayncClass(Context context) {
        this.context = context;
    }

    public void onPreExecute(){


    }
    @Override
    protected String doInBackground(String... params) {
        HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet(URL HERE);
        try{
            HttpResponse responseGiven = client.execute(get);
            StatusLine statusLine = responseGiven.getStatusLine();
            int statusCode = statusLine.getStatusCode();
            if(stat-usCode == 404){
            // you can not use toast in doInBackground function. you need to pass to progress
            publishProgress(0);
            }
        } catch(Exception e){

        }
        return null;
    }

    @Override
        protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
        Toast.makeText(context, "ERROR", Toast.LENGTH_SHORT).show();
        }

    public void onPostExecute(...){
        super.onPostExecute(s);

    }

}