自定義View學習小記

@Alu

先貼代碼：

public class CountView extends View {
private Paint mPaint;
private int millisecond;
private int hour;
private int minute;
private int second;
private Rect mBounds;
private Context context;
private boolean isRunning = false;
private Timer timer;
private StringBuffer stringBuffer;
private MyTask myTask;

public CountView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    this.context = context;
    mBounds = new Rect();
    mPaint = new Paint();
    stringBuffer = new StringBuffer();
    stringBuffer.append("00:00:00:00");

}
@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()){
        case MotionEvent.ACTION_DOWN:
            if (isRunning) {
                timer.cancel();
                timer.purge();
                timer = null;
                myTask = null;
                System.gc();
            } else {
                timer = new Timer();
                myTask = new MyTask();
                timer.schedule(myTask, 0, 10);
            }
            isRunning = !isRunning;
            break;
    }
    return false;
}
@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    mPaint.setColor(ContextCompat.getColor(context, R.color.colorPrimary));
    canvas.drawRect(0, 0, getWidth(), getHeight(), mPaint);
    mPaint.setColor(Color.WHITE);
    mPaint.setTextSize(60);
    String text = stringBuffer.toString();
    mPaint.getTextBounds(text, 0, text.length(), mBounds);
    float textWidth = mBounds.width();
    float textHeight = mBounds.height();
    canvas.drawText(text, getWidth() / 2 - textWidth / 2, getHeight() / 2 + textHeight / 2, mPaint);

}

private class MyTask extends TimerTask {

    @Override
    public void run() {
        stringBuffer.delete(0, stringBuffer.length());
        millisecond++;
        if (millisecond > 99) {
            millisecond = 0;
            second++;
        }
        if (second > 59) {
            second = 0;
            minute++;
        }

        if (minute > 59) {
            minute = 0;
            hour++;
        }
        if (hour < 10)
            stringBuffer.append(0).append(hour);
        else
            stringBuffer.append(hour);
        stringBuffer.append(":");
        if (minute < 10)
            stringBuffer.append(0).append(minute);
        else
            stringBuffer.append(minute);
        stringBuffer.append(":");
        if (second < 10)
            stringBuffer.append(0).append(second);
        else
            stringBuffer.append(second);
        stringBuffer.append(":");
        if (millisecond < 10)
            stringBuffer.append(0).append(millisecond);
        else
            stringBuffer.append(millisecond);
        handler.sendEmptyMessage(0);
    }

}

private Handler handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        if (msg.what == 0) {
            invalidate();
        }
    }
};

}
利用Handler+Timer來控制時間,StringBuffer和很簡單的算法來保存時間。
用法很簡單直接在布局中引用：

<com.alu.test.okletusgo.myview.view.CountView
    android:layout_width="150dp"
    android:layout_height="50dp"
    android:layout_centerInParent="true" />

稍加改造也可以有其他用途，例如 在抽獎之類的界面使用.

需要注意的：

在view的點擊事件里我做了:

timer = new Timer();  
myTask = new MyTask();

原因是個人多次嘗試，timer的run方法只會執(zhí)行 TimerTask 類的run();方法一次，所以手動去將之前用過的對象設置為 null 并調用 System.gc(); ,企圖回收對象,(感覺很笨，希望有人看了指點一下),再重新去設置一個新的 timer。
另外提一下 View 的 invalidate(); 方法需要在主線程執(zhí)行 ,這也是使用了handler的原因。

最后:

不求贊，只求提出問題，讓我改進學習。

修改暫停繼續(xù)的操作在 onTouch 的 ACTIONDOWN 情境下 。原因是對計時器的精準控制就應該體現(xiàn)在點下去的瞬間來控制跑秒。