3.?? 由主線程發送消息給子線程 ( 續 )

???? 上述范例里，是由子線程發送消息給主線程。本節將介紹如何從主線程 發送消息 給子線程。其方法是：當子線程執行 run() 函數時，就創建一個子線程的 Handler 對象。之后，當主線程執行 ac01 的 onClick() 函數時，就藉由此 Handler 對象引用而 push 消息給子線程。例如下述范例：

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//----- Looper_04 范例 ?-----

public ? class ?ac01? extends ?Activity? implements ?OnClickListener {

???? private ? final ? int ? WC ?= LinearLayout.LayoutParams. WRAP_CONTENT ;

???? private ? final ? int ? FP ?= LinearLayout.LayoutParams. FILL_PARENT ;

???? public ?TextView? tv ;

???? private ?myThread? t ;

???? private ?Button? btn ,? btn2 ;

???? private ?Handler? h ;

???? private ?Context? ctx ;

???? public ? void ?onCreate(Bundle icicle) {

???????????? super .onCreate(icicle);

???????????? ctx ?=? this ;

????????????????LinearLayout layout =? new ?LinearLayout( this );

????????????????layout.setOrientation(LinearLayout. VERTICAL );

??????????????????????????????

???????????????? btn ?=? new ?Button( this );

???????????????? btn .setId(101);

???????????????? btn .setBackgroundResource(R.drawable. heart );

???????????????? btn .setText( "test looper" );

???????????????? btn .setOnClickListener( this );

????????????????LinearLayout.LayoutParams param =

???????????????????? new ?LinearLayout.LayoutParams(100,50);

????????????????param. topMargin ?= 10;

????????????????layout.addView( btn , param);

???????????????

???????????????? btn2 ?=? new ?Button( this );

???????????????? btn2 .setId(102);

???????????????? btn2 .setBackgroundResource(R.drawable. ok_blue );

???????????????? btn2 .setText( "exit" );

???????????????? btn2 .setOnClickListener( this );

????????????????layout.addView( btn2 , param);

???????????????

???????????????? tv ?=? new ?TextView( this );

???????????????? tv .setTextColor(Color. WHITE );

???????????????? tv .setText( "" );

????????????????LinearLayout.LayoutParams param2 =

??????????????????? new ?LinearLayout.LayoutParams( FP ,? WC );

????????????????param2. topMargin ?= 10;

????????????????layout.addView( tv , param2);

????????????????setContentView(layout);?

???????????????? //------------------------

???????????????? t ?=? new ?myThread();

????????????????? t .start();

??????????}

?????????? public ? void ?onClick(View v) {

???????? switch (v.getId()){

???????? case ?101:

?????????????String obj =? "mainThread" ;

?????????????Message m =? h .obtainMessage(1, 1, 1, obj);

????????????? h .sendMessage(m);

????????????? break ;

???????? case ?102:

???????????? h .getLooper().quit();

????????finish();

???????????? break ;

????????}

????}

//------------------------------------------------?????

public ? class ?EventHandler? extends ?Handler {

?????????? public ?EventHandler(Looper looper) {

?????????????????????? super (looper);

??????????}

??????????? @Override

?????????????? public ? void ?handleMessage(Message msg) {

?????????????????????((Activity) ctx ).setTitle((String)msg. obj );

????????????}

????????}

//------------------------------------------------?????

class ?myThread? extends ?Thread{

????? public ? void ?run() {

?????????Looper. prepare ();

????????? h ?=? new ?Handler(){

??????????????? public ? void ?handleMessage(Message msg) {

??????????????????EventHandler ha =? new

?????????????????????EventHandler(Looper. getMainLooper ());

????????????????????String obj = (String)msg. obj ?+? ", myThread" ;

?????????????????????Message m = ha.obtainMessage(1, 1, 1, obj);

?????????????????????ha.sendMessage(m);

?????????}

?????????};

?????????Looper. loop ();

??????}

??}

}

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當子線程執行 run() 函數時，創建一個主線程的 EventHandler 對象，并且藉之而 push 消息給主線程了。就進行了兩個線程之間的互相交換消息，也是兩個函數或對象間之交換消息。此程序輸出畫面為：

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圖 2

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????? 上述范例定義了 Thread 的子類別。也可以將子線程包含到 Runnable 類別里，如下：

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//----- Looper_04aa 范例 ?-----

public ? class ?ac01? extends ?Activity? implements ?OnClickListener {

???? private ? final ? int ? WC ?= LinearLayout.LayoutParams. WRAP_CONTENT ;

???? private ? final ? int ? FP ?= LinearLayout.LayoutParams. FILL_PARENT ;

???? public ?TextView? tv ;

???? private ?RR? r ;

???? private ?Button? btn ,? btn2 ;

???? private ?Handler? h ;

???? private ?Context? ctx ;

???? public ? void ?onCreate(Bundle icicle) {

???????????? super .onCreate(icicle);

???????????? ctx ?=? this ;

????????????????LinearLayout layout =? new ?LinearLayout( this );

????????????????layout.setOrientation(LinearLayout. VERTICAL );

??????????????????????????????

???????????????? btn ?=? new ?Button( this );

???????????????? btn .setId(101);

???????????????? btn .setBackgroundResource(R.drawable. heart );

???????????????? btn .setText( "test looper" );

???????????????? btn .setOnClickListener( this );

????????????????LinearLayout.LayoutParams param =

???????????????????? new ?LinearLayout.LayoutParams(100,50);

????????????????param. topMargin ?= 10;

????????????????layout.addView( btn , param);

???????????????

???????????????? btn2 ?=? new ?Button( this );

???????????????? btn2 .setId(102);

???????????????? btn2 .setBackgroundResource(R.drawable. ok_blue );

???????????????? btn2 .setText( "exit" );

???????????????? btn2 .setOnClickListener( this );

????????????????layout.addView( btn2 , param);

???????????????

???????????????? tv ?=? new ?TextView( this );

???????????????? tv .setTextColor(Color. WHITE );

???????????????? tv .setText( "" );

????????????????LinearLayout.LayoutParams param2 =

??????????????????? new ?LinearLayout.LayoutParams( FP ,? WC );

????????????????param2. topMargin ?= 10;

????????????????layout.addView( tv , param2);

????????????????setContentView(layout);?

???????????????? //------------------------

???????????????? r ?=? new ?RR();

?????????}

?????????? public ? void ?onClick(View v) {

???????? switch (v.getId()){

???????? case ?101:

?????????????String obj =? "mainThread" ;

?????????????Message m =? h .obtainMessage(1, 1, 1, obj);

????????????? h .sendMessage(m);

????????????? break ;

???????? case ?102:

???????????? h .getLooper().quit();

????????finish();

???????????? break ;

????????}

????}

//------------------------------------------------??????

public ? class ?EventHandler? extends ?Handler {

?????????? public ?EventHandler(Looper looper) {

?????????????????????? super (looper);

??????????}

??????????? @Override

?????????????? public ? void ?handleMessage(Message msg) {

?????????????????????((Activity) ctx ).setTitle((String)msg. obj );

????????????}

????????}

//------------------------------------------------?????

public ? class ?RR? implements ?Runnable {

???? public ?RR() {

????????Thread aThread =? new ?Thread( null ,? this ,? "RR" );

????????aThread.start();

????}

???? public ? void ?run() {

?????????Looper. prepare ();

????????? h ?=? new ?Handler(){

??????????????? public ? void ?handleMessage(Message msg) {

??????????????????EventHandler ha =? new ?EventHandler(Looper. getMainLooper ());

????????????????????String obj = (String)msg. obj ?+? ", myThread" ;

?????????????????????Message m = ha.obtainMessage(1, 1, 1, obj);

?????????????????????ha.sendMessage(m);

?????????}

?????????};

?????????Looper. loop ();

??????}

??}

}

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當子線程執行到 RR() 函數時，創建一個子線程，并執行 run() 函數，就將 消息發送 給主線程了。

活用Android的Message Queue(3)