android - Android中一个线程可以重复使用吗？

Question

我正在使用一个线程来运行 5 秒的计时器，当该计时器用完时，我想更改一些变量并再次启动它，重复此过程直到不满足特定条件。我一直在研究线程，显然它们不能被重置或再次使用，但必须创建另一个线程。我想不出正确的方法。

这是我的代码:

package com.deucalion0;

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

public class FirstOneActivity extends Activity {
/** Called when the activity is first created. */


MediaPlayer  ourSong;
int counter;
Button add;
Thread timer;
TextView display;
TextView lvl;
int level = 1;
int time;




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

    ourSong = MediaPlayer.create(FirstOneActivity.this, R.raw.click);
    counter = 0;
    add = (Button) findViewById (R.id.bAdd);
    display = (TextView) findViewById (R.id.tvDisplay);
    lvl = (TextView) findViewById (R.id.lvldisplay);

    add.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            counter++;
            //ourSong.start();
            display.setText("Your total is "+ counter);

            if(counter ==1)

            { 
                set();
            }   
        }
    });


     timer = new Thread(){
        public void run(){
            try{
                sleep(time);
            }catch(InterruptedException e){
                e.printStackTrace();
            }finally{
                test();

            }
        }


    };

}


public void test(){ // Method that does two things after the timer runs out, depending on the value held in counter

 if(counter>= 10 && level == 1 || counter>= 15 && level == 2)
    {       
        level++;
        counter =0;
        display.setText("Your total is 0");

        //The timer must be reset for the next level


    }

     else if(counter<10 && level == 1 || counter< 15 && level == 2){

        Intent openNext = new Intent("com.deucalion0.NEXT");
        startActivity(openNext);
    }


}


public void set(){


      if(level == 1)
    {   lvl.setText("Level is "+ level);
        time = 5000; // The value passed to the sleep method in the thread, this is the length of the timer
    }

    else if (level == 2)
    {lvl.setText("Level is "+level);
        time = 5000;
    }   

}


}

所以基本上我想继续使用该线程，但根据级别为它传递不同的时间限制，为了测试我现在只编写了前两个级别。

如果对此有任何见解，我将不胜感激。谢谢。

我的代码的修订版使用了此处答案中的一些帮助，但我仍然遇到问题:

package com.deucalion0;

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

public class FirstOneActivity extends Activity {
/** Called when the activity is first created. */


MediaPlayer  ourSong;
int counter;
Button add;
Thread timer;
TextView display;
TextView lvl;
int level = 1;
int time;
boolean completed = false;


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

    ourSong = MediaPlayer.create(FirstOneActivity.this, R.raw.click);
    counter = 0;
    add = (Button) findViewById (R.id.bAdd);
    display = (TextView) findViewById (R.id.tvDisplay);
    lvl = (TextView) findViewById (R.id.lvldisplay);

    add.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            counter++;
            completed=false;
            //ourSong.start();
            display.setText("Your total is "+ counter);

            if(counter ==1)

            {   
                set();
                timer.start(); // start the timer loop:
            }   
        }
    });


    // create a Handler for the thread to use when interacting with the UI
    final Handler handler = new Handler();

    // create the timer object
    timer = new Thread() {
        public void run() {
            // create a Runnable that will execute on the UI thread
            Runnable updater = new Runnable() {
                public void run() {

                }
            };

            while (!completed) {
                try {
                    sleep(time);
                } catch(InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    handler.post(updater);
                    test();
                }
            }
        }
    };




}

public void reset()//Resets the variables so the level increments, the counter is reset to 0 
{
    completed=true;
    level++;
    counter =0;

}


public void test(){ // Method that does two things after the timer runs out, depending on the value held in counter

 if(counter>= 10 && level == 1 || counter>= 15 && level == 2)
    {   
        reset();    
    }

     else if(counter<10 && level == 1 || counter< 15 && level == 2){

        Intent openNext = new Intent("com.deucalion0.NEXT");
        startActivity(openNext);
    }
}


public void set(){


      if(level == 1)
    {   lvl.setText("Level is "+ level);
        time = 5000; // The value passed to the sleep method in the thread, thi is the length of the timer
    }

    else if (level == 2)
    {lvl.setText("Level is "+level);
        time = 5000;
    }   
}
}

游戏运行并在计数器 = 1 时启动计时器，但如果我在计时器用完后按下按钮，我会由于异常而强制关闭。我需要做的是，如果在 5 秒内按下超过 9 次点击，计数器将重置为 0，级别变为 2。以下是 LogCat 中的错误:

02-29 09:47:36.313: D/AndroidRuntime(279): Shutting down VM
02-29 09:47:36.313: W/dalvikvm(279): threadid=1: thread exiting with uncaught exception     (group=0x4001d800)
02-29 09:47:36.333: E/AndroidRuntime(279): FATAL EXCEPTION: main
02-29 09:47:36.333: E/AndroidRuntime(279): java.lang.IllegalThreadStateException:     Thread already started.
02-29 09:47:36.333: E/AndroidRuntime(279):  at java.lang.Thread.start(Thread.java:1322)
02-29 09:47:36.333: E/AndroidRuntime(279):  at com.deucalion0.FirstOneActivity$1.onClick(FirstOneActivity.java:51)
02-29 09:47:36.333: E/AndroidRuntime(279):  at android.view.View.performClick(View.java:2408)
02-29 09:47:36.333: E/AndroidRuntime(279):  at android.view.View$PerformClick.run(View.java:8816)
02-29 09:47:36.333: E/AndroidRuntime(279):  at android.os.Handler.handleCallback(Handler.java:587)
02-29 09:47:36.333: E/AndroidRuntime(279):  at android.os.Handler.dispatchMessage(Handler.java:92)
02-29 09:47:36.333: E/AndroidRuntime(279):  at android.os.Looper.loop(Looper.java:123)
02-29 09:47:36.333: E/AndroidRuntime(279):  at android.app.ActivityThread.main(ActivityThread.java:4627)
02-29 09:47:36.333: E/AndroidRuntime(279):  at java.lang.reflect.Method.invokeNative(Native Method)
02-29 09:47:36.333: E/AndroidRuntime(279):  at java.lang.reflect.Method.invoke(Method.java:521)
02-29 09:47:36.333: E/AndroidRuntime(279):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
02-29 09:47:36.333: E/AndroidRuntime(279):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
02-29 09:47:36.333: E/AndroidRuntime(279):  at dalvik.system.NativeStart.main(Native Method)

我希望这些信息有助于说明我的问题。

Answer 1

作为一般规则，Thread 对象可以start() 调用任意多次。每次调用 start() 都会启动一个新线程。其他类似线程的对象(例如 AsyncTask 、 TimerTask )通常只能执行一次。

但是，您的计时器线程不会像写的那样工作。 test()方法修改显示，需要在UI线程上运行。

一种方法是创建一个 Handler并从计时器线程向处理程序发送一个 Runnable，然后处理程序调用 test()。还有其他方法，但这个方法可能涉及对现有代码的最少修改。

你应该考虑使用 AsyncTask 来做你想做的事。您还应该启用 StrictMode在开发时帮助检测任何线程错误。

这是对您的代码的简单修改，它将完成我认为您正在尝试做的事情:

// create a Handler for the thread to use when interacting with the UI
final Handler handler = new Handler();

// create the timer object
timer = new Thread() {
    public void run() {
        // create a Runnable that will execute on the UI thread
        Runnable updater = new Runnable() {
            public void run() {
                test();
            }
        }
        while (!exitConditionMet()) {
            try {
                sleep(time);
            } catch(InterruptedException e) {
                e.printStackTrace();
            } finally {
                handler.post(updater);
            }
        }
    }
};

// start the timer loop:
timer.start();

上面的代码假定有一个方法 exitConditionMet() 在线程应该退出时返回 true。