Question

我根据亲爱的Mayank编辑了我的代码＆＃39;回答但它没有显示在方法开始之前在displayMsg（）方法中作为输入发送的任何消息。我应该说使用nfc和方法onNewIntent启动MethodTest（）（意图）

@Override
protected void onNewIntent(Intent intent) {
   MethodTest();
    ..............

}

public void MethodTest() {
    DisplayMsg("method 1 is running");
    Method1();

    DisplayMsg("method 2 is running");
    Method2();

    DisplayMsg("method 3 is running");
    Method3();

}

private int DisplayMsg(String msg) {
    totalMsg += msg;
    DisplayMsgClass dc = new DisplayMsgClass();
    dc.doInBackground(totalMsg);
}

private class DisplayMsgClass extends AsyncTask<String, Integer, String> {

    @Override
    protected void onPreExecute() {
         textView.setText("Hello !!!");
        progressBar = (ProgressBar) findViewById(R.id.progressBar1);
        progressBar.setVisibility(View.VISIBLE);
        super.onPreExecute();
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);

    }

    @Override
    protected String doInBackground(String... Messages) {


        return Messages[0];
    }

    @Override
    protected void onPostExecute(String result) {
        progressBar.setVisibility(View.INVISIBLE);

        textView.setText(result);
    }
}

在我的布局中：

<LinearLayout>
<ProgressBar
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:visibility="gone"
    android:id="@+id/progressBar1"
    />
 <TextView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:id="@+id/textv1"
  android:hint="AppletPass"
  android:gravity="center"/>
 </LinearLayout>

Answer 1

请记住，理想情况下，AsyncTasks应该用于短操作（最多几秒钟。）

尝试了解有关AsyncTask的更多信息，但代码中存在很多错误

请勿手动拨打doInBackground()。

dc.doInBackground(totalMsg); //错误
多次调用DisplayMsg（），每次创建一个新的DisplayMsgClass类实例

DisplayMsgClass dc = new DisplayMsgClass(); //错误
onPreExecute()
textView.setText("Hello !!!"); // NullPointerException。调用textView.setText()时不会初始化它。

警告

不要在同一个地方打电话给AsyncTask.execute()多个人例如：

DisplayMsgClass displayMsgClass = new DisplayMsgClass();  
displayMsgClass.execute();  
displayMsgClass.execute(); //Error, IllegalStateException

将根据您的实现向您展示基本演示，您可以根据自己的方式进行修改。

public void MethodTest() {

    // execute task
    new DisplayMsgClass().execute("Download now");
}

/*
public void MethodTest() {
    DisplayMsg("method 1 is running");
    Method1();

    DisplayMsg("method 2 is running");
    Method2();

    DisplayMsg("method 3 is running");
    Method3();

}

private int DisplayMsg(String msg) {
    totalMsg += msg;
    DisplayMsgClass dc = new DisplayMsgClass();
    dc.doInBackground(totalMsg);
}
*/

private class DisplayMsgClass extends AsyncTask<String, Integer, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        // retrieve the widgets
        progressBar = (ProgressBar) findViewById(R.id.progressBar1);
        textView = (TextView) findViewById(R.id.textv1);


        textView.setText("Download initialized");
        progressBar.setVisibility(View.VISIBLE);
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);
    }

    @Override
    protected String doInBackground(String... Messages) {

        // read commands
        String command = Messages[0];
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "Download completed";
    }

    @Override
    protected void onPostExecute(String result) {

        //invoked on the UI thread after the background computation finishes
        progressBar.setVisibility(View.INVISIBLE);
        textView.setText(result);
    }
}

Answer 2

您在if（...）结尾处看到调用onProgressUpdate(Progress...)的原因是因为publishProgress(Progress... values)将消息发布到内部处理程序，此内部处理程序稍后会处理消息以更新进展。换句话说，publishProgress(Progress... values)不会同步调用onProgressUpdate(Progress...)请参阅此处的实施：https://github.com/android/platform_frameworks_base/blob/master/core/java/android/os/AsyncTask.java#L649

这是必要的，因为publishProgress(Progress... values)应该从doInBackground(Params...)调用，它位于工作线程上，用于AsyncTask，而onProgressUpdate(Progress...)发生在 UI线程，以便UI可以反映进度更改。通过在UI线程上向处理程序发布消息，可以将进度信息从工作线程同步到UI线程，而不会阻塞任一线程。

Answer 3

尝试以下代码

private int DisplayMsg(String msg) {
    totalMsg += msg;
    DisplayMsgClass dc = new DisplayMsgClass();
    dc.runner.execute(totalMsg);
}

希望它能运作

:) GlbMP

Answer 4

在xml布局中创建进度条并默认设置其可见性并将代码创建为样本

// AsyncTask。

    private class DownloadWebPageTask extends AsyncTask<String, Integer, String> {

    @Override
    protected void onPreExecute() {
        //textView.setText("Hello !!!");
        progressBar = (ProgressBar) findViewById(R.id.progressBar1);
        progressBar.setVisibility(View.VISIBLE);
        super.onPreExecute();
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);

    }

    @Override
    protected String doInBackground(String... urls) {
        String response = "";
        for (String url : urls) {
            DefaultHttpClient client = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(url);
            try {
                HttpResponse execute = client.execute(httpGet);
                InputStream content = execute.getEntity().getContent();

                BufferedReader buffer = new BufferedReader(new InputStreamReader(
                        content));
                String s = "";
                while ((s = buffer.readLine()) != null) {
                    response += s;
                }

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

    @Override
    protected void onPostExecute(String result) {
        progressBar.setVisibility(View.INVISIBLE);
        textView.setText(result);
    }
}

进度对话框未在屏幕上显示

4 个答案: