Updating UI with Runnable & postDelayed not working with timer app

问题

I have looked at every discussion and thread I can find on getting this to work but it is not. I have a simple timer that updates a text view (mTimeTextField in the example below). The mUpdateTimeTask run method is being executed correctly (every second) but the UI/text field is not being updated.

I have code based on the info found here:

http://android-developers.blogspot.com/2007/11/stitch-in-time.html http://developer.android.com/resources/articles/timed-ui-updates.html

Here is the code:

package com.something.handlertest;

import com.something.handlertest.R;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.SystemClock;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class Test extends Activity {

    private Handler mHandler = new Handler(); 
    private int labelNo    = 0;
    private long currTime  = 0L;
    private long mStartTime = 0L;
    TextView mTimeTextField;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mTimeTextField = (TextView)findViewById(R.id.timeTextFieldl);

        Button startButton = (Button)findViewById(R.id.start_button);
        startButton.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                   if (mStartTime == 0L) {
                        mStartTime = System.currentTimeMillis();
                        mHandler.removeCallbacks(mUpdateTimeTask);
                        mHandler.postDelayed(mUpdateTimeTask, 100);
                   }
            }
        });
    }

    private Runnable mUpdateTimeTask = new Runnable() {
           public void run() {
               final long start = mStartTime;
               //long millis = SystemClock.uptimeMillis() - start;
               long millis = SystemClock.uptimeMillis();
               int seconds = (int) (millis / 1000);
               int minutes = seconds / 60;
               seconds     = seconds % 60;

               //setContentView(mTimeTextField);  This will blow up if I use it

               if (seconds < 10) {
                   mTimeTextField.setText("" + minutes + ":0" + seconds);
               } else {
                   mTimeTextField.setText("" + minutes + ":" + seconds);            
               }

               //mHandler.postAtTime(this,
                   //    start + (((minutes * 60) + seconds + 1) * 1000));

               mHandler.postAtTime(this, 1000);
           }
        };

}

Per some suggestions, I have tried adding:

setContentView(mTimeLabel);

But this will crash complain about the view not having a parent. FYI, I do have a:

setContentView(R.layout.main);

call in my onCreate().

回答1:

Replace

mHandler.postAtTime(this, 1000);

with

mHandler.postDelayed(this, 1000);

回答2:

You need to do UI updates in the UI thread.

You need to create a Handler in the UI thread to run tasks in the UI thread.

public class MainActivity extends AppCompatActivity
    private Handler mHandler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        mHandler = new Handler(); // This to create the Handler in the UI thread
        // ...
    }

回答3:

This might be more along the lines of what you are looking for:

private Runnable mUpdateTimeTask = new Runnable() {
       public void run() {

           final long start = mStartTime;
           long elapseTime = System.currentTimeMillis() - start;
           int seconds = (int) (elapseTime / 1000);
           int minutes = seconds / 60;
           seconds     = seconds % 60;

           if (seconds < 10) {
               mTimeTextField.setText("" + minutes + ":0" + seconds);
           } else {
               mTimeTextField.setText("" + minutes + ":" + seconds);            
           }

           // add a delay to adjust for computation time
           long delay = (1000 - (elapseTime%1000));

           mHandler.postDelayed(this, delay);
       }
    };

I found this to be a good way to add a time to video's

回答4:

view can only be displayed on UI thread. you have to start the runnable using ru

回答5:

Please ensure R.id.timeTextFieldl is a correct id.

回答6:

if (seconds < 10) {
    mTimeTextField.setText("" + minutes + ":0" + seconds);
} else {
    mTimeTextField.setText("" + minutes + ":" + seconds);            
}

shorter is:

mTimeTextField.setText(minutes + ":" + (seconds < 10 ? "0" : "") + seconds);

but better way is using String.format^

mTimeTextField.setText(String.format("%d:%s%d", minutes, (seconds < 10 ? "0" : ""), seconds);

来源：https://stackoverflow.com/questions/3765161/updating-ui-with-runnable-postdelayed-not-working-with-timer-app

标签

android

multithreading

timer

handler

postdelayed