Android Studio--從Java線程到安卓線程

簡述：

相信很多學安卓的都是從java入門之後開始進行安卓的學習，而當我們面臨安卓線程的書寫的時候，發現安卓線程並不是我們想象中使用java的線程寫法就可以。

這裡我們簡單的書寫一個TextClock（由TextView 和Calendar組成），這裡的Button用於終止時間。這裡我們使用java上線程的寫法來：

public class MainActivity extends AppCompatActivity {

    private TextView textView;
    private boolean flag = true;//用於控制線程
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new Thread(new Runnable() {
            @Override
            public void run() {
                while(flag){
                    Calendar calendar = Calendar.getInstance();
                    calendar.setTimeInMillis(System.currentTimeMillis());
                    int hour = calendar.get(Calendar.HOUR_OF_DAY);
                    int minute = calendar.get(Calendar.MINUTE);
                    int sec = calendar.get(Calendar.SECOND);
                    String string = new String(hour + " : " + minute + " : " + sec);
                    textView = (TextView)findViewById(R.id.test);
                    textView.setText(msg.obj.toString());
                    try{
                        Thread.currentThread().sleep(100);
                    }catch(Exception e){
                        e.printStackTrace();
                    }
                }
            }
        }).start();
        Button button = (Button)findViewById(R.id.Btn);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                flag = false;
                Toast.makeText(MainActivity.this,"You click here!",Toast.LENGTH_SHORT).show();
            }
        });
    }
}

　　現在分析一下上面的案例，在上面的程序中有兩個線程：一個主線程和一個子線程，它們的職責如圖所示。

上述實例中的處理利用子線程進行了UI界面的更新，違背了Android多線程編程規則，系統會拋出異常“Only the original thread that created a view hierarchy can touch its views”。

要解決這個問題，就要明確主線程和子線程的職責。主線程的職責是創建、顯示和更新UI控件、處理UI事件、啟動子線程、停止子線程;子線程的職責是計算逝去的時間和向主線程發出更新UI消息，而不是直接更新UI。<喎?/kf/ware/vc/" target="_blank" class="keylink">vc3Ryb25nPjwvcD4NCjxwPjxzdHJvbmc+1vfP37PMtcTWsNTwysfP1Mq+VUm/2Lz+oaK0psDtVUnKwrz+oaLG9Lav19PP37PMoaLNo9a519PP37PMus24/NDCVUmjrNfTz9+zzLXE1rDU8MrHvMbL48rFyKW1xMqxvOS6zc/y1vfP37PMt6Kz9rj80MJVSc/7z6Kho7WrysfQwrXEzsrM4tPWs/bP1sHLo7rX08/fs8y6zdb3z9+zzMjnus63osvNz/vPoqGiyOe6zs2o0MXE2D88L3N0cm9uZz48L3A+DQrA+9PDSGFuZGxlcrrNbWVzc2FnZbSmwO3X0734s8w8YnIgLz4NCtPJ09qyvL7Wuty88rWlo6zO0sPH1eLA77K7vfjQ0LK8vta0+sLrtcSy+8r2o6zS1M/CzqrW97vutq+0+sLro7oNCjxwcmUgY2xhc3M9"brush:java;"> public class MainActivity extends AppCompatActivity { private TextView textView; private boolean flag = true; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); /*使用Handler進行更新頁面*/ final android.os.Handler handler = new android.os.Handler(){ @Override public void handleMessage(Message msg) { switch(msg.what){/*接收來自子線程之間的message*/ case 0:{/*根據來源執行不同的操作*/ textView = (TextView)findViewById(R.id.test); textView.setText(msg.obj.toString());/*文本更新*/ } } super.handleMessage(msg); //這裡最好對不需要或者不關心的消息拋給父類，避免丟失消息 } }; new Thread(new Runnable() {//利用Runnable接口實現線程 @Override public void run() { while(flag){ Calendar calendar = Calendar.getInstance(); calendar.setTimeInMillis(System.currentTimeMillis()); int hour = calendar.get(Calendar.HOUR_OF_DAY); int minute = calendar.get(Calendar.MINUTE); int sec = calendar.get(Calendar.SECOND); String string = new String(hour + " : " + minute + " : " + sec); //上述為計算操作 Message message = new Message();//初始化消息對象 message.obj = string;//將想要發送的消息添加到消息中 message.what = 0;//設置message來源為0 handler.sendMessage(message);//給handler發送消息 try{//線程休眠 Thread.currentThread().sleep(100); //Thread代表線程,currentThread()代表獲取當前線程,sleep()代表睡眠 }catch(Exception e){ e.printStackTrace(); } } } }).start(); Button button = (Button)findViewById(R.id.Btn); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { flag = false; Toast.makeText(MainActivity.this,"You click here!",Toast.LENGTH_SHORT).show(); } }); } }

這樣子我們就簡單的做了一個計時器app，利用線程成功實現了計時並更新數據。

public class MainActivity extends AppCompatActivity {

    private TextView textView;
    private android.os.Handler handler;
    private boolean flag = true;
    Timer timer = new Timer();//實例化Timer
    TimerTask timerTask = new TimerTask() {//實例化TimerTask
        @Override
        public void run() {
            Calendar calendar = Calendar.getInstance();
            calendar.setTimeInMillis(System.currentTimeMillis());
            int hour = calendar.get(Calendar.HOUR_OF_DAY);
            int minute = calendar.get(Calendar.MINUTE);
            int sec = calendar.get(Calendar.SECOND);
            String string = new String(hour + " : " + minute + " : " + sec);
            Message message = new Message();//實例消息
            message.obj = string;
            message.what = 0;
            handler.sendMessage(message);
        }
    };


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        handler = new android.os.Handler(){
            @Override
            public void handleMessage(Message msg) {
                switch(msg.what){
                    case 0:{
                        textView = (TextView)findViewById(R.id.test);
                        textView.setText(msg.obj.toString());
                    }
                }
                super.handleMessage(msg);
            }
        };
        timer.schedule(timerTask,1000,100);//注釋一

        Button button = (Button)findViewById(R.id.Btn);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                flag = false;
                Toast.makeText(MainActivity.this,"You click here!",Toast.LENGTH_SHORT).show();
            }
        });
    }
}