Android高手进阶教程(十九)之---Android开发中，使用线程应该注意的问题!

我们都知道Hanlder是线程与Activity通信的桥梁，我们在开发好多应用中会用到线程，有些人处理不当，会导致当程序结束时，线程并没有被销毁，而是一直在后台运行着，当我们重新启动应用时，又会重新启动一个线程，周而复始，你启动应用次数越多，开启的线程数就越多，你的机器就会变得越慢。

为了方便 大家理解，我写一个简单的Demo.功能就是每2秒中将应用的Title更换一次。具体步骤如下:

第一步:新建一个Android工程命名为ThreadDemo。

第二步:修改ThreadDemo.java,代码如下:

package com.tutor.thread;   import android.app.Activity;   import android.os.Bundle;   import android.os.Handler;   import android.util.Log;   public class ThreadDemo extends Activity {       private static final String TAG = "ThreadDemo";       private int count = 0;       private Handler mHandler =  new Handler();              private Runnable mRunnable = new Runnable() {                      public void run() {               //为了方便 查看，我们用Log打印出来               Log.e(TAG, Thread.currentThread().getName() + " " +count);               count++;               setTitle("" +count);               //每2秒执行一次               mHandler.postDelayed(mRunnable, 2000);           }                  };       @Override      public void onCreate(Bundle savedInstanceState) {           super.onCreate(savedInstanceState);           setContentView(R.layout.main);            //通过Handler启动线程           mHandler.post(mRunnable);       }          }

package com.tutor.thread; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.util.Log; public class ThreadDemo extends Activity { private static final String TAG = "ThreadDemo"; private int count = 0; private Handler mHandler = new Handler(); private Runnable mRunnable = new Runnable() { public void run() { //为了方便 查看，我们用Log打印出来 Log.e(TAG, Thread.currentThread().getName() + " " +count); count++; setTitle("" +count); //每2秒执行一次 mHandler.postDelayed(mRunnable, 2000); } }; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //通过Handler启动线程 mHandler.post(mRunnable); } }

第三步:运行上述工程，查看运行效果:

当然上面不是重点，退出应用时，线程还在跑，打开Logcat视窗或者cmd终端查看，如下(刚吃了午餐回来，线程还在跑着):

当我们再次启动应用时，会重新启动一个新的线程，如下图所示:

所以我们在应用退出时，要将线程销毁，我们只要在Activity中的，onDestory()方法处理一下就OK了，如下代码所示:

@Override    protected void onDestroy() {       mHandler.removeCallbacks(mRunnable);       super.onDestroy();     }

@Override protected void onDestroy() { mHandler.removeCallbacks(mRunnable); super.onDestroy(); }

所以ThreadDemo.java的完整代码如下:

package com.tutor.thread;   import android.app.Activity;   import android.os.Bundle;   import android.os.Handler;   import android.util.Log;   public class ThreadDemo extends Activity {       private static final String TAG = "ThreadDemo";       private int count = 0;       private Handler mHandler =  new Handler();              private Runnable mRunnable = new Runnable() {                      public void run() {               //为了方便 查看，我们用Log打印出来               Log.e(TAG, Thread.currentThread().getName() + " " +count);               count++;               setTitle("" +count);               //每2秒执行一次               mHandler.postDelayed(mRunnable, 2000);           }                  };       @Override      public void onCreate(Bundle savedInstanceState) {           super.onCreate(savedInstanceState);           setContentView(R.layout.main);            //通过Handler启动线程           mHandler.post(mRunnable);       }              @Override      protected void onDestroy() {           //将线程销毁掉           mHandler.removeCallbacks(mRunnable);           super.onDestroy();       }   }

package com.tutor.thread; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.util.Log; public class ThreadDemo extends Activity { private static final String TAG = "ThreadDemo"; private int count = 0; private Handler mHandler = new Handler(); private Runnable mRunnable = new Runnable() { public void run() { //为了方便 查看，我们用Log打印出来 Log.e(TAG, Thread.currentThread().getName() + " " +count); count++; setTitle("" +count); //每2秒执行一次 mHandler.postDelayed(mRunnable, 2000); } }; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //通过Handler启动线程 mHandler.post(mRunnable); } @Override protected void onDestroy() { //将线程销毁掉 mHandler.removeCallbacks(mRunnable); super.onDestroy(); } }

Ok~今天就写到这里，我午休去也~大家有不明白的可以留言！