java - android中周期性任务的实现

Question

我想创建一个小的 android 应用程序，它会在单击按钮后定期显示系统时间（即设置活动）......通过Intent创建按钮和设置定期活动的代码如下所示：

package com.example.timeupdate;

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

public class MainActivity extends Activity {

Button button;
TextView show;

@Override
protected void onCreate(Bundle I_Love_Biriyani) {
    super.onCreate(I_Love_Biriyani);
    setContentView(R.layout.activity_main);

    button = (Button) findViewById (R.id.pressButton);
    show = (TextView) findViewById (R.id.Show);

    button.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub

            Intent openTimeUpdater = new Intent("com.example.timeupdate.TIMEUPDATER");
            startActivity(openTimeUpdater);

        }
    });

}


@Override
protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();
    finish();
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}



}

这是重复计时器的代码（比如说 5 秒），我使用TimerTask类来执行这项工作：

package com.example.timeupdate;

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class TimeUpdater extends Activity {

    TextView Show;

    TimerTask timer= new TimerTask(){

        @Override
        public void run() {
            // TODO Auto-generated method stub
            Date d = new Date();
            Show.setText(""+d);
        }

    };

    @Override
    protected void onCreate(Bundle hotovaga) throws IllegalStateException {
        // TODO Auto-generated method stub
        super.onCreate(hotovaga);
        setContentView(R.layout.new_update);

        Show = (TextView) findViewById (R.id.time);

        Timer t = new Timer();
        t.scheduleAtFixedRate(timer , 0 , 5000);

    }


}

单击按钮后，时间仅显示一次，然后应用程序停止显示对话框消息。需要解释才能以同样的方式完成这项工作。

Answer 1

您正在尝试访问非 UI 线程内的 UI 元素。

Show.setText(""+d);

相反，将其包装在runOnUiThread接口中以获得正确的输出。

TimeUpdater为您的课程使用以下代码

public class TimeUpdater extends Activity {


    TextView Show = null;
    Calendar c; 
    int seconds;
    int minutes;
    int hours;

    TimerTask timer= new TimerTask(){

        @Override
        public void run() {
            c = Calendar.getInstance();
            seconds = c.get(Calendar.SECOND);
            minutes = c.get(Calendar.MINUTE);
            hours = c.get(Calendar.HOUR);

            runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    Show.setText(hours + ":" + minutes + ":" + seconds);
                }
            });
        }

    };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.new_update);

        Show = (TextView) findViewById (R.id.time);

        Timer t = new Timer();
        t.scheduleAtFixedRate(timer , 0 , 5000);


    }

}

Answer 2

将实际的 Timer (java.util.Timer) 与 runOnUiThread() 结合使用是解决此问题的一种方法，下面是如何实现它的示例。

public class myActivity extends Activity {

private Timer myTimer;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.main);
    myTimer = new Timer();
    myTimer.schedule(new TimerTask() {
        @Override
        public void run() {
            TimerMethod();
        }

    }, 0, 1000);
}

private void TimerMethod()
{
    //This method is called directly by the timer
    //and runs in the same thread as the timer.

    //We call the method that will work with the UI
    //through the runOnUiThread method.
    this.runOnUiThread(Timer_Tick);
}

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

    //This method runs in the same thread as the UI. 
    // Set your textView data here.              

    //Do something to the UI thread here

    }
};
}

Answer 3

使用 Play-Service 的 PeriodicTask，它是 Google 最新的用于安排工作背景的工具。