亚洲在线久爱草,狠狠天天香蕉网,天天搞日日干久草,伊人亚洲日本欧美

截獲Handler要接收的消息

Handler 作用：1 更新UI, 2發送消息，處理消息

---轉：
ｈａｎｄｌｅｒ總結：<br>
1.不能直接在非UI線程直接更新UＩ（大多數時候）。<br>
2.每次創建Handler時需要給它綁定一個looper，如果是主線程不給定具體的looper則會綁定默認的looper。<br>
3.子線程運行時一定要調用start（）方法。<br>
４.在某些特殊情況下在非UI線程是可以更新UI的／／不推薦使用（當剛啟動Activity即onCreate里面此時onResume方法還沒有執行的時候可以，因為在線程中更新UI時會調用ViewParent.invalidateChild()方法檢查當前的Thread是否是UIThread，若為UIThread則可以更新（ViewParent是一個接口類，其實現是ViewRootImpl;invalidateChild()方法調用checkThread()方法來檢查線程是否為主線程）。ViewRootImp是在onResume方法中初始化的，所以只要在ViewRootImpl創建之前更新UI（在onCreate方法中創建線程并執行，此時還沒有初始化ViewRootImp），就可以逃避掉checkThread()的檢查進而更新UI。）<br>
５．更新ＵＩ的四種方式：<br>
ａ＞使用ｈａｎｄｌｅｒ．ｐｏｓｔ方法<br>
ｂ＞使用ｈａｎｄｌｅｒ．ｓｅｎｄＭｅｓｓａｇｅ方法，用ｈａｎｌｅＭｅｓｓａｇｅ方法更新ＵＩ。<br>
ｃ＞用ｒｕｎＯｎＵｉＴｈｒｅａｄ方法。<br>
ｄ＞使用ｖｉｅｗ．ｐｏｓｔ方法。<br>
６．ＨanｄｌｅｒＴｈｒｅａｄ本質是子線程，在創建子線程的ｈａｎｄｌｅｒ時綁定的是ｈａｎｄｌｅｒＴｈｒｅａｄ對象的ｇｅｔＬｏｏｐｅｒ（）。

---摘自評論區 ? 在ViewRootImpl沒有實例化的時候是不會check是否是主線程，也就是說，在非UI線程中是可以更新UI的，但是為了線程安全的原因，系統會強制要求只能在主線程中更新UI（猜測）。之所以說沒有太大的意義是因為實際開發中是不會有這種情況的，谷歌官方也是說了只能在UI線程更新UI，這頂多算是一個BUG吧，看不懂的朋友們知道就行了，不用深究~ 非UI線程能否更新UI

非UI線程能否更新UI --->剛啟動的時候，立即在非UI線程更新->不報錯。 --->休眠2s鐘以后，更新——————>報錯 更新UI-->會調用checkForRelayout()方法 -->invalidate()方法-->invalidate(true)方法，關注viewParent-->ViewRootImpl是ViewParent的實現類 --->p.invalidateChild()-->查看ViewRootImpl.invalidateChild()-->checkThread()方法-->判斷UI線程是否是當前線程，不想等拋出異常。 ViewRootImpl是onResume(）方法才會創建。所以onCreate()方法中要延遲才可以。 handleResumeActivity()方法---》viewManager.addView()-->ViewRootImpl初始化。，關注viewParent-->ViewRootImpl是ViewParent的實現類

?2

Android中更新UI的幾種方式:
1.?
public?void?activityUpdateUI(){
??runOnUiThread(new?Runnable()?{
?????@Override
?????public?void?run()?{
?????????textView.setText("Changed?by?Activity");
?????}
??});
}

2.?
public?void?handlerChangeUI(){
??handler.post(new?Runnable(){
?????@Override
?????public?void?run()?{
????????textView.setText("OK");
?????}
??});
}

3.?
public?void?handlerChangeUI2(){
???handler.sendEmptyMessage(1);
}
4.?view.post()
public?void?viewUpdateUI(){
??textView.post(new?Runnable()?{
?????@Override
?????public?void?run()?{
???????textView.setText("UI?was?updated?by?view.post");
?????}
??});
}
通過源碼我們可以發現:
handler使用post()去發送一個Runnable，其實它內部也是封裝了Message去發送的，本質上和直接發送Message沒有區別；
runOnUiThread()方法會判斷當前線程是不是UI線程，不是的話，則調用Activity自己的Handler對象，通過該對象發送一個Runnable；如果是，則調用UI線程的run()方法。
View的post()方法會判斷?attachInfo?是否為空。如果不為空，則通過?attachInfo?的Handler對象去post一個Runnable對象。如果為空，則調用ViewRootImpl的getRunQueue去拿到一個Handler去post一個Runnable對象。
綜上，更新UI的四種方法，本質上都是通過Handler機制去更新UI的。

public?class?Main2?extends?Activity?implements?View.OnClickListener?{
????int?aaa=0;
????Button?button1,button2;

????Handler?handler=new?Handler(){
????????@Override
????????public?void?handleMessage(Message?msg)?{
????????????Message?message=new?Message();
????????????System.out.println("Handler");

????????????threadHandler.sendMessageDelayed(message,1000);
????????}
????};
????
????Handler?threadHandler;
????@Override
????protected?void?onCreate(@Nullable?Bundle?savedInstanceState)?{
????????super.onCreate(savedInstanceState);
????????setContentView(R.layout.main2);
????????button1=(Button)?findViewById(R.id.button1);
????????button2=(Button)?findViewById(R.id.button2);
????????button1.setOnClickListener(this);
????????button2.setOnClickListener(this);
????????HandlerThread?thread=new?HandlerThread("threadHandler");
????????thread.start();

????????threadHandler=new?Handler(thread.getLooper()){
????????????@Override
????????????public?void?handleMessage(Message?msg)?{
????????????????Message?message=new?Message();
????????????????System.out.println("ThreadHandler");
????????????????aaa++;
????????????????System.out.println(aaa);
????????????????if(aaa<5)?{
????????????????????handler.sendMessageDelayed(message,?1000);
????????????????}
????????????}
????????};
????}

????@Override
????public?void?onClick(View?view)?{
????????switch?(view.getId()){
????????????case?R.id.button1:
????????????????handler.sendEmptyMessage(1);
????????????????break;
????????????case?R.id.button2:
????????????????handler.removeMessages(0);
????????????????threadHandler.removeMessages(0);
????????????????break;
????????????default:
????????????????break;
????????}
????}
}

public?class?Main?extends?AppCompatActivity?implements?View.OnClickListener{

????private?TextView?textView;
????private?ImageView?imageView;
????Button?btn;
????Handler?handler=new?Handler(new?Handler.Callback()?{
????????@Override
????????public?boolean?handleMessage(Message?message)?{
????????????Toast.makeText(getApplicationContext(),""+222,Toast.LENGTH_SHORT).show();
????????????return?false;
????????}
????}){
????????@Override
????????public?void?handleMessage(Message?msg)?{
????????????super.handleMessage(msg);
????????????textView.setText(msg.obj.toString());
????????????Toast.makeText(getApplicationContext(),""+111,Toast.LENGTH_SHORT).show();
????????}
????};

????private?int?imagesId[]={R.drawable.hy1,R.drawable.hy2,R.drawable.hy3};
????private?MyRunnable?myRunnable=new?MyRunnable();
????int?index;

????@Override
????public?void?onClick(View?view)?{
????????handler.removeCallbacks(myRunnable);
????}

????class?Person{
????????public?int?age;
????????public?String?name;

????????@NonNull
????????@Override
????????public?String?toString()?{
????????????return?"age:"+age+"?name:"+name;
????????}
????}

????class?MyRunnable?implements?Runnable?{

????????@Override
????????public?void?run()?{
????????????index++;
????????????index=index%3;
????????????imageView.setImageResource(imagesId[index]);
????????????handler.postDelayed(myRunnable,1000);

????????}
????}
????
????@Override
????protected?void?onCreate(@Nullable?Bundle?savedInstanceState)?{
????????super.onCreate(savedInstanceState);
????????setContentView(R.layout.activity_main);
????????textView=(TextView)?findViewById(R.id.tv);
????????textView.setText("hh");
????????imageView=(ImageView)?findViewById(R.id.imageView);
????????btn=(Button)findViewById(R.id.button);
????????btn.setOnClickListener(this);
????????handler.postDelayed(myRunnable,1000);

????????new?Thread(){
????????????@Override
????????????public?void?run()?{
????????????????super.run();
????????????????try?{
????????????????????Thread.sleep(1000);
????????????????????handler.post(new?Runnable()?{
????????????????????????@Override
????????????????????????public?void?run()?{
????????????????????????????/*textView.setText("爺");
????????????????????????????handler.sendEmptyMessage(1);*/
????????????????????????}
????????????????????});

????????????????}?catch?(InterruptedException?e)?{
????????????????????e.printStackTrace();
????????????????}
????????????????Person?person=new?Person();
????????????????person.age=18;
????????????????person.name="爺";
????????????????Message?message=handler.obtainMessage();
????????????????message.obj=person;
????????????????message.sendToTarget();
????????????}
????????}.start();

????}

}

new?Thread()?{
	public?void?run()?{
		try?{
			Thread.sleep(1000);
			handler.post(new?Runnable()?{
		????????????????@Override
				public?void?run()?{
				????????//?TODO?Auto-generated?method?stub
				????????//?更新文本信息
				????????//?此時直接在這里更新ui的時候,程序將會直接崩潰掉
				????????textView.setText("更新了");
			????????}
		????????});
				
	?????????}?catch?(InterruptedException?e)?{
		????????//?TODO?Auto-generated?catch?block
		????????e.printStackTrace();
	?????????}
????????};
}.start();
從上面的方法中我們可以知道,如果想直接更新ui,我們需要在Thread的run方法中通過
handler.post()的方法來實現,而post方法中的參數是一個new?Runnable(){public?void?run(){}
,然后我們在這個run方法中去更新ui,這才是正確的方法

handler原理圖解：

handler原理：

ViewRootImpl是在WindowManagerGlobal類中的

ActivityThread中

checkThread()

View的invalidateChild(View child)

View的invalidate方法源碼