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Handler实现倒计时

程序员文章站 2022-07-14 17:05:18
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通过Handler实现一个倒计时的功能

具体代码如下:

MainActivity.java

public class MainActivity extends AppCompatActivity {

    public static final int COUNTDOWN_TIME_CODE = 10001;
    public static final int DELAY_MILLIS = 1000;
    public static final int MAX_COUNT = 10;
    public static final int MIN_COUNT = 0;
    private TextView mCountDownText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mCountDownText = (TextView) findViewById(R.id.coun_down_num);
        CountingHandler handler = new CountingHandler(this);
        //通过CountingHandler发送Message
        Message message = Message.obtain();
        message.what = COUNTDOWN_TIME_CODE;
        message.arg1 = MAX_COUNT;
        //设置延迟发送时间1s
        handler.sendMessageDelayed(message, DELAY_MILLIS);
    }
    /**
     * 实现CountingHandler类,利用弱引用避免内存泄漏
     */

    public static class CountingHandler extends Handler{
        final WeakReference<MainActivity> mWeakReference;
        //构造方法传入MainActivity
        public CountingHandler(MainActivity activity) {
            mWeakReference = new WeakReference<>(activity);
        }

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            //通过activity得到TextView控件
            MainActivity activity = mWeakReference.get();
            switch (msg.what){
                case COUNTDOWN_TIME_CODE:
                    int value = msg.arg1;
                        //更新UI
                        activity.mCountDownText.setText(String.valueOf(--value));
                        if (value > MIN_COUNT) {
                            //新建message将value作为参数
                            Message message = Message.obtain();
                            message.what = COUNTDOWN_TIME_CODE;
                            message.arg1 = value;
                            sendMessageDelayed(message, DELAY_MILLIS);
                    }
                    break;
            }
        }
    }
}


通过新建一个静态类CountingHandler,避免内存泄漏,原理是通过弱引用MainActivity及时的将内存释放,而不是一直引用。

运行结果便是UI的TextView 每隔1s从10减到0。是通过sendMessageDelay()方法实现的。