探寻Android的线程问题

// version 1
public class iamathread extends thread {
  public iamathread() {
    super("iamathread");
  }
 
  @override
  public void run() {
     
// your code (sequence of instructions)
  }
}
// to execute this sequence of instructions in a separate thread.
new iamathread().start();
 
// version 2
public class iamarunnable implements runnable {
  @override
  public void run() {
     
// your code (sequence of instructions)
  }
}
// to execute this sequence of instructions in a separate thread.
iamarunnable myrunnable = new iamarunnable();
new thread(myrunnable).start();
 

> a handler allows you to send and process message and runnable objects associated with a thread's messagequeue. each handler instance is associated with a single thread and that thread's message queue. when you create a new handler, it is bound to the thread/message queue of the thread that is creating it — from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue.

public class testactivity extends activity {
 
// ...
// all standard stuff
 
@override
public void oncreate(bundle savedinstancestate) {
 
   
// ...
   
// all standard stuff
 
   
// we're creating a new handler here
   
// and we're in the ui thread (default)
   
// so this handler is associated with the ui thread
  handler mhandler = new handler();
 
   
// i want to start doing something really long
   
// which means i should run the fella in another thread.
   
// i do that by sending a message - in the form of another runnable object
 
   
// but first, i'm going to create a runnable object or a message for this
  runnable mrunnableonseparatethread = new runnable() {
    @override
    public void run () {
 
       
// do some long operation
      longoperation();
 
       
// after mrunnableonseparatethread is done with it's job,
       
// i need to tell the user that i'm done
       
// which means i need to send a message back to the ui thread
 
       
// who do we know that's associated with the ui thread?
      mhandler.post(new runnable(){
        @override
        public void run(){
           
// do some ui related thing
           
// like update a progress bar or textview
           
// ....
        }
      });
 
 
    }
  };
 
   
// cool but i've not executed the mrunnableonseparatethread yet
   
// i've only defined the message to be sent
   
// when i execute it though, i want it to be in a different thread
   
// that was the whole point.
 
  new thread(mrunnableonseparatethread).start();
}
 
}

// the below code is inside a textwatcher
// which implements the ontextchanged method
// i've simplified it to only highlight the parts we're
// interested in
 
private long lastchange = 0;
 
@override
public void ontextchanged(final charsequence chars,
             int start, int before, int count) {
 
     
// the handler is spawned from the ui thread
    new handler().postdelayed(
 
       
// argument 1 for postdelated = message to be sent
      new runnable() {
        @override
        public void run() {
 
          if (nochangeintext_inthelastfewseconds()) {
            searchandpopulatelistview(chars.tostring()); 
// logic
          }
        }
      },
 
       
// argument 2 for postdelated = delay before execution
      300);
 
    lastchange = system.currenttimemillis();
}
 
 
private boolean nochangeintext_inthelastfewseconds() {
  return system.currenttimemillis() - lastchange >= 300
}

class looperthread extends thread { 
 public handler mhandler; 
 
 public void run() { 
  looper.prepare(); //创建本线程的looper并创建一个messagequeue
 
  mhandler = new handler() { 
   public void handlemessage(message msg) { 
    // process incoming messages here 
   } 
  }; 
 
  looper.loop(); //开始运行looper,监听message queue 
 } 
}

public class listprogressdemo extends listactivity { 
 
 @override
 public void oncreate(bundle savedinstancestate) { 
  super.oncreate(savedinstancestate); 
  setcontentview(r.layout.listprogress); 
 
  ((button) findviewbyid(r.id.load_handler)).setonclicklistener(new view.onclicklistener(){ 
 
   @override
   public void onclick(view view) { 
    data = null; 
    data = new arraylist<string>(); 
 
    adapter = null; 
 
    showdialog(progress_dialog); 
    new progressthread(handler, data).start(); 
   } 
  }); 
 } 
 
 @override
 protected dialog oncreatedialog(int id) { 
  switch(id) { 
  case progress_dialog: 
     return progressdialog.show(this, "", 
     "loading. please wait...", true); 
 
  default: return null; 
  } 
 } 
 
 private class progressthread extends thread { 
 
  private handler handler; 
  private arraylist<string> data; 
 
  public progressthread(handler handler, arraylist<string> data) { 
   this.handler = handler; 
   this.data = data; 
  } 
 
  @override
  public void run() { 
   for (int i=0; i<8; i++) { 
    data.add("listitem"); //后台数据处理
    try { 
     thread.sleep(100); 
    }catch(interruptedexception e) { 
      
     message msg = handler.obtainmessage(); 
     bundle b = new bundle(); 
     b.putint("state", state_error); 
     msg.setdata(b); 
     handler.sendmessage(msg); 
      
    } 
   } 
   message msg = handler.obtainmessage(); 
   bundle b = new bundle(); 
   b.putint("state", state_finish); 
   msg.setdata(b); 
   handler.sendmessage(msg); 
  } 
   
 } 
 
 // 此处甚至可以不需要设置looper，因为handler默认就使用当前线程的looper
 private final handler handler = new handler(looper.getmainlooper()) {
 
  public void handlemessage(message msg) { // 处理message，更新listview
   int state = msg.getdata().getint("state"); 
   switch(state){ 
    case state_finish: 
     dismissdialog(progress_dialog); 
     toast.maketext(getapplicationcontext(), 
       "加载完成!", 
       toast.length_long) 
       .show(); 
 
     adapter = new arrayadapter<string>(getapplicationcontext(), 
       android.r.layout.simple_list_item_1, 
       data ); 
        
     setlistadapter(adapter); 
 
     break; 
 
    case state_error: 
     dismissdialog(progress_dialog); 
     toast.maketext(getapplicationcontext(), 
       "处理过程发生错误!", 
       toast.length_long) 
      .show(); 
 
     adapter = new arrayadapter<string>(getapplicationcontext(), 
       android.r.layout.simple_list_item_1, 
       data ); 
        
      setlistadapter(adapter); 
 
      break; 
 
    default: 
 
   } 
  } 
 }; 
 
 
 private arrayadapter<string> adapter; 
 private arraylist<string> data; 
 
 private static final int progress_dialog = 1; 
 private static final int state_finish = 1; 
 private static final int state_error = -1; 
} 

((button) findviewbyid(r.id.load_asynctask)).setonclicklistener(new view.onclicklistener(){ 
 
 @override
 public void onclick(view view) { 
  data = null; 
  data = new arraylist<string>(); 
 
  adapter = null; 
 
  //显示progressdialog放到asynctask.onpreexecute()里 
  //showdialog(progress_dialog); 
  new progresstask().execute(data); 
 } 
}); 
 
private class progresstask extends asynctask, void, integer> { 
 
/* 该方法将在执行实际的后台操作前被ui thread调用。可以在该方法中做一些准备工作，如在界面上显示一个进度条。*/
@override
protected void onpreexecute() { 
 // 先显示progressdialog
 showdialog(progress_dialog); 
} 
 
/* 执行那些很耗时的后台计算工作。可以调用publishprogress方法来更新实时的任务进度。 */
@override
protected integer doinbackground(arraylist<string>... datas) { 
 arraylist<string> data = datas[0]; 
 for (int i=0; i<8; i++) { 
  data.add("listitem"); 
 } 
 return state_finish; 
} 
 
/* 在doinbackground 执行完成后，onpostexecute 方法将被ui thread调用， 
 * 后台的计算结果将通过该方法传递到ui thread. 
 */
@override
protected void onpostexecute(integer result) { 
 int state = result.intvalue(); 
 switch(state){ 
 case state_finish: 
  dismissdialog(progress_dialog); 
  toast.maketext(getapplicationcontext(), 
    "加载完成!", 
    toast.length_long) 
    .show(); 
 
  adapter = new arrayadapter<string>(getapplicationcontext(), 
    android.r.layout.simple_list_item_1, 
    data ); 
     
  setlistadapter(adapter); 
 
  break; 
   
 case state_error: 
  dismissdialog(progress_dialog); 
  toast.maketext(getapplicationcontext(), 
    "处理过程发生错误!", 
    toast.length_long) 
   .show();
 
  adapter = new arrayadapter<string>(getapplicationcontext(), 
    android.r.layout.simple_list_item_1, 
    data );
 
   setlistadapter(adapter);
 
   break;
 
 default:
 
 }
}