Android画个时钟玩玩

先看下最终的效果

开始实现

新建一个ClockView集成View

    public class ClockView extends View {    }

先重写onMeasure方法，这里要先说一下View的测量模式，一共有三种：

• EXACTLY

  即精确值模式，当我们将控件的layout_width属性或layout_height属性指定为具体数值时，比如android:layout_width="100dp"，或者指定为math_parent属性时（占据父View的大小），系统使用的是EXACTLY模式。

• AT_MOST

  即最大值模式，当控件的layout_width属性或layout_height属性指定为wrap_content时，控件大小一般随着控件的子控件或内容的变化而变化，此时控件的尺寸只要不超过父控件允许的最大尺寸即可。

• UNSPECIFIED

  这个属性比较奇怪——它不指定其大小测量模式，View想多大就多大，通常情况下在绘制自定义View时才会使用。

  因为View的onMeasure方法只支持EXACTLY模式，当layout_width和layout_height为wrap_content时，View的大小就显得很奇怪了，如下图。

  

所以我们重写一下onMeasure方法可以指定View width、height的最小值

    /**     * 当布局为wrap_content时设置默认长宽     * @param widthMeasureSpec     * @param heightMeasureSpec     */    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        setMeasuredDimension(measure(widthMeasureSpec), measure(heightMeasureSpec));    }    private int measure(int origin){        int result = DEFAULT_MIN_WIDTH;        int specMode = MeasureSpec.getMode(origin);        int specSize = MeasureSpec.getSize(origin);        if(specMode == MeasureSpec.EXACTLY){            result = specSize;        }else{            if(specMode == MeasureSpec.AT_MOST){                result = Math.min(result, specSize);            }        }        return result;    }

下面就是最重要的重写onDraw方法来绘制表盘、刻度、指针……，大致流程如下

• 画表盘，用drawCircle绘制一个圆作为表盘, 圆心坐标为(getWidth()/2, getHeight()/2)，半径为Math.min(getHeight()/2, getWidth()/2)。

//画外圆float borderWidth = DEFAULT_BORDER_WIDTH;Paint paintCircle = new Paint();paintCircle.setStyle(Paint.Style.STROKE);paintCircle.setAntiAlias(true);paintCircle.setStrokeWidth(borderWidth);canvas.drawCircle(getWidth() / 2, getHeight() / 2, Math.min(getHeight() / 2, getWidth() / 2) - borderWidth / 2, paintCircle);

• 画刻度线，在这里我们可以利用一个`canvas.rotate’方法就可以不用计算角度了

//画刻度线float degreeLength = 0f;Paint paintDegree = new Paint();paintDegree.setAntiAlias(true);for(int i=0;i<60;i++){    if(i % 5 == 0){        paintDegree.setStrokeWidth(6);        degreeLength = DEFAULT_LONG_DEGREE_LENGTH;    }else{        paintDegree.setStrokeWidth(3);        degreeLength = DEFAULT_SHORT_DEGREE_LENGTH;    }    canvas.drawLine(getWidth()/2, Math.abs(getWidth()/2 - getHeight()/2), getWidth()/2, Math.abs(getWidth()/2 - getHeight()/2) + degreeLength, paintDegree);    canvas.rotate(360/60, getWidth()/2, getHeight()/2);}

• 画刻度上的数字

//刻度数字int degressNumberSize = 30;canvas.translate(getWidth() / 2, getHeight() / 2);Paint paintDegreeNumber = new Paint();paintDegreeNumber.setTextAlign(Paint.Align.CENTER);paintDegreeNumber.setTextSize(degressNumberSize);paintDegreeNumber.setFakeBoldText(true);for(int i=0;i<12;i++){    float[] temp = calculatePoint((i+1)*30, r - DEFAULT_LONG_DEGREE_LENGTH - degressNumberSize/2 - 15);    canvas.drawText((i+1)+"", temp[2], temp[3] + degressNumberSize/2-6, paintDegreeNumber);}/** * 根据角度和长度计算线段的起点和终点的坐标 * @param angle * @param length * @return */private float[] calculatePoint(float angle, float length){    float[] points = new float[4];    if(angle <= 90f){        points[0] = -(float) Math.sin(angle*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[1] = (float) Math.cos(angle*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[2] = (float) Math.sin(angle*Math.PI/180) * length;        points[3] = -(float) Math.cos(angle*Math.PI/180) * length;    }else if(angle <= 180f){        points[0] = -(float) Math.cos((angle-90)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[1] = -(float) Math.sin((angle-90)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[2] = (float) Math.cos((angle-90)*Math.PI/180) * length;        points[3] = (float) Math.sin((angle-90)*Math.PI/180) * length;    }else if(angle <= 270f){        points[0] = (float) Math.sin((angle-180)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[1] = -(float) Math.cos((angle-180)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[2] = -(float) Math.sin((angle-180)*Math.PI/180) * length;        points[3] = (float) Math.cos((angle-180)*Math.PI/180) * length;    }else if(angle <= 360f){        points[0] = (float) Math.cos((angle-270)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[1] = (float) Math.sin((angle-270)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;        points[2] = -(float) Math.cos((angle-270)*Math.PI/180) * length;        points[3] = -(float) Math.sin((angle-270)*Math.PI/180) * length;    }    return points;}

• 画指针

//画指针Paint paintHour = new Paint();paintHour.setAntiAlias(true);paintHour.setStrokeWidth(15);Paint paintMinute = new Paint();paintMinute.setAntiAlias(true);paintMinute.setStrokeWidth(10);Paint paintSecond = new Paint();paintSecond.setAntiAlias(true);paintSecond.setStrokeWidth(5);Calendar now = Calendar.getInstance();float[] hourPoints = calculatePoint(now.get(Calendar.HOUR_OF_DAY)%12/12f*360, hourPointerLength);canvas.drawLine(hourPoints[0], hourPoints[1], hourPoints[2], hourPoints[3], paintHour);float[] minutePoints = calculatePoint(now.get(Calendar.MINUTE)/60f*360, minutePointerLength);canvas.drawLine(minutePoints[0], minutePoints[1], minutePoints[2], minutePoints[3], paintMinute);float[] secondPoints = calculatePoint(now.get(Calendar.SECOND)/60f*360, secondPointerLength);canvas.drawLine(secondPoints[0], secondPoints[1], secondPoints[2], secondPoints[3], paintSecond);

• 画圆心

//画圆心Paint paintCenter = new Paint();paintCenter.setColor(Color.WHITE);canvas.drawCircle(0, 0, 2, paintCenter);

最后只要启动一个无限循环的线程，每隔1秒针重绘一下View就能让指针动起来了

private Thread timeThread = new Thread() {    @Override    public void run() {        try {            while(true){                updateHandler.sendEmptyMessage(0);                Thread.sleep(1000);            }        } catch (InterruptedException e) {            e.printStackTrace();        }    }};private Handler updateHandler = new Handler() {    @Override    public void handleMessage(Message msg) {        invalidate();    }};

全部测试代码下载地址:

https://github.com/hellsam/clockdemo_android

欢迎留言交流，如有描述不当或错误的地方还请留言告知

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