android - 使用 Runnable 和 postDelayed 更新 UI 不适用于计时器应用程序

Question

我已经查看了我可以找到的所有讨论和线程，但事实并非如此。我有一个简单的计时器来更新文本视图（下面示例中的 mTimeTextField）。mUpdateTimeTask 运行方法正在正确执行（每秒），但 UI/文本字段未更新。

我有基于此处找到的信息的代码：

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

这是代码：

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);
           }
        };

}

---

根据一些建议，我尝试添加：

setContentView(mTimeLabel);

但这会崩溃抱怨没有父母的观点。仅供参考，我确实有一个：

setContentView(R.layout.main);

打电话给我onCreate()。

Answer 1

代替

mHandler.postAtTime(this, 1000);

和

mHandler.postDelayed(this, 1000);

Answer 2

1. 您需要在 UI 线程中进行 UI 更新。

2. 您需要在 UI 线程中创建一个 Handler 以在 UI 线程中运行任务。

   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
           // ...
       }
   

Answer 3

这可能更符合您正在寻找的内容：

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);
       }
    };

我发现这是为视频添加时间的好方法

Answer 4

视图只能显示在 UI 线程上。你必须使用 ru 启动 runnable

Answer 5

请确保 R.id.timeTextFieldl 是正确的 id。

Answer 6

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

更短的是：

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

但更好的方法是使用 String.format^

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