在学习安卓群英传自定义控件章节的时候，有一个例子是绘制时钟，在实现了书上的例子后就想看这个时钟能不能动起来。

这里选择延迟一秒发送消息重绘view来实现的动画，对外提供了开启时钟，关闭时钟的方法，当activity执行onResume方法的时候，执行startClock()方法，当移除view或activity执行onStop方法的时候可以执行stopClock()方法。

首先根据view的宽高来确定圆心的位置，并画出一个圆。再通过view高度的一半减去圆的半径，确定刻度的起始位置，选择刻度的长度并绘制出来。然后再刻度下方绘制出数字。最终将画布进行旋转，时钟总共有60个刻度，循环旋转，每次旋转6度即可。

最后是绘制指针，通过计算算出指针对应每个刻度的X,Y坐标并绘制直线。

代码实现

自定义控件的代码：

public class ClockView extends View{ private Paint circlePaint,dialPaint,numberPaint; //view 的宽高 private float mWidth,mHeight; //圆的半径 private float circleRadius; //圆心X,Y坐标 private float circleX,circleY; private int second,minute; private double hour; private Handler handler = new Handler(Looper.getMainLooper()){ @Override public void handleMessage(Message msg) { super.handleMessage(msg); if(msg.what==0){ invalidate(); } } }; public ClockView(Context context, AttributeSet attrs) { super(context, attrs); initPaint(); } private void initPaint(){ //刻盘圆，小时刻度，时针和分针的画笔 circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG); circlePaint.setColor(Color.BLACK); circlePaint.setStyle(Paint.Style.STROKE); circlePaint.setStrokeWidth(10); //分钟刻度的画笔 dialPaint = new Paint(Paint.ANTI_ALIAS_FLAG); dialPaint.setColor(Color.BLACK); dialPaint.setStrokeWidth(5); //数字的画笔 numberPaint = new Paint(Paint.ANTI_ALIAS_FLAG); numberPaint.setColor(Color.BLACK); numberPaint.setStrokeWidth(5); numberPaint.setTextSize(30); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); mWidth = getMeasuredWidth(); mHeight = getMeasuredHeight(); if(mWidth<mHeight){ //圆的半径为view的宽度的一半再减9，防止贴边 circleRadius = mWidth/2-9; circleX = mWidth/2; circleY = mHeight/2; } else{ circleRadius = mHeight/2-9; circleX = mWidth/2; circleY = mHeight/2; } } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); setTimes(); drawCirclePoint(canvas); drawCircle(canvas); drawDial(canvas); drawPointer(canvas); } /**圆心 * @param canvas */ private void drawCirclePoint(Canvas canvas){ canvas.drawCircle(circleX,circleY,5,circlePaint); } private void drawCircle(Canvas canvas){ canvas.drawCircle(circleX,circleY,circleRadius,circlePaint); } /**画刻度及时间 * @param canvas */ private void drawDial(Canvas canvas){ //时钟用长一点的刻度，画笔用画圆的画笔 Point hourStartPoint = new Point(circleX,circleY-circleRadius); Point hourEndPoint = new Point(circleX,circleY-circleRadius+40); //分钟的刻度要稍微短一些，画笔用画圆的画笔 Point startPoint2 = new Point(circleX,circleY-circleRadius); Point endPoint2 = new Point(circleX,circleY-circleRadius+10); //开始画刻度和数字，总共60个刻度，12个时钟刻度，被5整除画一个时钟刻度，被其余的为分针刻度 String clockNumber; for(int i=0;i<60;i++){ if(i%5==0){ if(i==0){ clockNumber = "12"; } else{ clockNumber = String.valueOf(i/5); } //时针刻度 canvas.drawLine(hourStartPoint.getX(),hourStartPoint.getY(),hourEndPoint.getX(),hourEndPoint.getY(),circlePaint); //画数字，需在时针刻度末端加30 canvas.drawText(clockNumber,circleX-numberPaint.measureText(clockNumber)/2,hourEndPoint.getY()+30,numberPaint); } else{ //画分针刻度 canvas.drawLine(startPoint2.getX(),startPoint2.getY(),endPoint2.getX(),endPoint2.getY(),circlePaint); } //画布旋转6度 canvas.rotate(360/60,circleX,circleY); } } /**画指针 * X点坐标 cos(弧度)*r * Y点坐标 sin(弧度)*r * toRadians将角度转成弧度 * 安卓坐标系与数学坐标系不同的地方是X轴是相反的，所以为了调整方向，需要将角度+270度 * @param canvas */ private void drawPointer(Canvas canvas){ canvas.translate(circleX,circleY); float hourX = (float) Math.cos(Math.toRadians(hour*30+270))*circleRadius*0.5f; float hourY = (float) Math.sin(Math.toRadians(hour*30+270))*circleRadius*0.5f; float minuteX = (float) Math.cos(Math.toRadians(minute*6+270))*circleRadius*0.8f; float minuteY = (float) Math.sin(Math.toRadians(minute*6+270))*circleRadius*0.8f; float secondX = (float) Math.cos(Math.toRadians(second*6+270))*circleRadius*0.8f; float secondY = (float) Math.sin(Math.toRadians(second*6+270))*circleRadius*0.8f; canvas.drawLine(0,0,hourX,hourY,circlePaint); canvas.drawLine(0,0,minuteX,minuteY,circlePaint); canvas.drawLine(0,0,secondX,secondY,dialPaint); //一秒重绘一次 handler.sendEmptyMessageDelayed(0,1000); } public void startClock(){ setTimes(); invalidate(); } private void setTimes(){ Date date = new Date(); Calendar calendar = Calendar.getInstance(); calendar.setTime(date); second = getTimes(date,Calendar.SECOND); minute = getTimes(date,Calendar.MINUTE); hour = getTimes(date,Calendar.HOUR)+minute/12*0.2; } private int getTimes(Date date,int calendarField){ Calendar calendar = Calendar.getInstance(); calendar.setTime(date); return calendar.get(calendarField); } public void stopClock(){ handler.removeMessages(0); }}

public class Point {
private float x;
private float y;

public Point(float x, float y) { this.x = x; this.y = y;}public float getX() { return x;}public void setX(float x) { this.x = x;}public float getY() { return y;}public void setY(float y) { this.y = y;}

Acitivity：

public class ClockActivity extends Activity{ private ClockView clockView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.clock_layout); clockView = (ClockView) findViewById(R.id.clock); } @Override protected void onResume() { super.onResume(); clockView.startClock(); } @Override protected void onStop() { super.onStop(); clockView.stopClock(); } }

xml布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:gravity="center" android:layout_height="match_parent"> <com.example.customview.view.ClockView android:layout_width="match_parent" android:id="@+id/clock" android:layout_height="match_parent" /></LinearLayout>

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