Android之自定义View以及画一个时钟

https://www.2cto.com/kf/201509/443112.html

概述：

当Android自带的View满足不了开发者时，自定义View就发挥了很好的作用。
建立一个自定义View，需要继承于View类，并且实现其中的至少一个构造函数和两个方法：onMeasure（）和onDraw（）；
onMeasure()用于设置自定义View的尺寸，onDraw()用于绘制View中的内容。

在onDraw()方法中，需要调用画笔绘制图形或文本，绘制的模板时Canvas对象， Canvas类中用来绘制图形文本的方法有：

drawRect(RectF rect, Paint paint) //绘制区域，参数一为RectF一个区域

drawPath(Path path, Paint paint) //绘制一个路径，参数一为Path路径对象

drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint) //贴图，参数一就是我们常规的Bitmap对象，参数二是源区域(这里是bitmap)，参数三是目标区域(应该在canvas的位置和大小)，参数四是Paint画刷对象，因为用到了缩放和拉伸的可能，当原始Rect不等于目标Rect时性能将会有大幅损失。

drawLine(float startX, float startY, float stopX, float stopY, Paintpaint) //画线，参数一起始点的x轴位置，参数二起始点的y轴位置，参数三终点的x轴水平位置，参数四y轴垂直位置，最后一个参数为Paint 画刷对象。

drawPoint(float x, float y, Paint paint) //画点，参数一水平x轴，参数二垂直y轴，第三个参数为Paint对象。

drawText(String text, float x, floaty, Paint paint) //渲染文本，Canvas类除了上面的还可以描绘文字，参数一是String类型的文本，参数二x轴，参数三y轴，参数四是Paint对象。

drawOval(RectF oval, Paint paint)//画椭圆，参数一是扫描区域，参数二为paint对象；

drawCircle(float cx, float cy, float radius,Paint paint)// 绘制圆，参数一是中心点的x轴，参数二是中心点的y轴，参数三是半径，参数四是paint对象；

drawArc(RectF oval, float startAngle, float sweepAngle, boolean useCenter, Paint paint)//画弧，参数一是RectF对象，一个矩形区域椭圆形的界限用于定义在形状、大小、电弧，参数二是起始角(度)在电弧的开始，参数三扫描角(度)开始顺时针测量的，参数四是如果这是真的话,包括椭圆中心的电弧,并关闭它,如果它是假这将是一个弧线,参数五是Paint对象。

绘制图形需要画笔Paint对象，Paint类中的方法有：

setARGB(int a, int r, int g, int b) // 设置 Paint对象颜色，参数一为alpha透明值

setAlpha(int a) // 设置alpha不透明度，范围为0~255

setAntiAlias(boolean aa) // 是否抗锯齿

setColor(int color) // 设置颜色，这里Android内部定义的有Color类包含了一些常见颜色定义

setTextScaleX(float scaleX) // 设置文本缩放倍数，1.0f为原始

setTextSize(float textSize) // 设置字体大小

setUnderlineText(booleanunderlineText) // 设置下划线

public class MyView extends View {

 

    private int width;

    private int height;

    private Paint mPaintLine;

    private Paint mPaintCircle;

    private Paint mPaintHour;

    private Paint mPaintMinute;

    private Paint mPaintSec;

    private Paint mPaintText;

    private Calendar mCalendar;

    public static final int NEED_INVALIDATE = 0X23;

 

    //每隔一秒，在handler中调用一次重新绘制方法

    private Handler handler = new Handler(){

        @Override

        public void handleMessage(Message msg) {

 

            switch (msg.what){

                case NEED_INVALIDATE:

                    mCalendar = Calendar.getInstance();

                    invalidate();//告诉UI主线程重新绘制

                    handler.sendEmptyMessageDelayed(NEED_INVALIDATE,1000);

                    break;

                default:

                    break;

            }

        }

    };

 

    public MyView(Context context) {

        super(context);

    }

 

    public MyView(Context context, AttributeSet attrs) {

        super(context, attrs);

 

        mCalendar = Calendar.getInstance();

 

        mPaintLine = new Paint();

        mPaintLine.setColor(Color.BLUE);

        mPaintLine.setStrokeWidth(10);

 

        mPaintCircle = new Paint();

        mPaintCircle.setColor(Color.GREEN);//设置颜色

        mPaintCircle.setStrokeWidth(10);//设置线宽

        mPaintCircle.setAntiAlias(true);//设置是否抗锯齿

        mPaintCircle.setStyle(Paint.Style.STROKE);//设置绘制风格

 

        mPaintText = new Paint();

        mPaintText.setColor(Color.BLUE);

        mPaintText.setStrokeWidth(10);

        mPaintText.setTextAlign(Paint.Align.CENTER);

        mPaintText.setTextSize(40);

 

        mPaintHour = new Paint();

        mPaintHour.setStrokeWidth(20);

        mPaintHour.setColor(Color.BLUE);

 

        mPaintMinute = new Paint();

        mPaintMinute.setStrokeWidth(15);

        mPaintMinute.setColor(Color.BLUE);

 

        mPaintSec = new Paint();

        mPaintSec.setStrokeWidth(10);

        mPaintSec.setColor(Color.BLUE);

 

        handler.sendEmptyMessage(NEED_INVALIDATE);//向handler发送一个消息，让它开启重绘

    }

 

    @Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

        height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);

        setMeasuredDimension(width, height);

    }

 

    @Override

    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

 

        int circleRadius = 400;

        //画出大圆

        canvas.drawCircle(width / 2, height / 2, circleRadius, mPaintCircle);

        //画出圆中心

        canvas.drawCircle(width / 2, height / 2, 20, mPaintCircle);

        //依次旋转画布，画出每个刻度和对应数字

        for (int i = 1; i <= 12; i++) {

            canvas.save();//保存当前画布

            canvas.rotate(360/12*i,width/2,height/2);

            //左起：起始位置x坐标，起始位置y坐标，终止位置x坐标，终止位置y坐标，画笔(一个Paint对象)

            canvas.drawLine(width / 2, height / 2 - circleRadius, width / 2, height / 2 - circleRadius + 30, mPaintCircle);

            //左起：文本内容，起始位置x坐标，起始位置y坐标，画笔

            canvas.drawText(+i, width / 2, height / 2 - circleRadius + 70, mPaintText);

            canvas.restore();//

        }

 

        int minute = mCalendar.get(Calendar.MINUTE);//得到当前分钟数

        int hour = mCalendar.get(Calendar.HOUR);//得到当前小时数

        int sec = mCalendar.get(Calendar.SECOND);//得到当前秒数

 

        float minuteDegree = minute/60f*360;//得到分针旋转的角度

        canvas.save();

        canvas.rotate(minuteDegree, width / 2, height / 2);

        canvas.drawLine(width / 2, height / 2 - 250, width / 2, height / 2 + 40, mPaintMinute);

        canvas.restore();

 

        float hourDegree = (hour*60+minute)/12f/60*360;//得到时钟旋转的角度

        canvas.save();

        canvas.rotate(hourDegree, width / 2, height / 2);

        canvas.drawLine(width / 2, height / 2 - 200, width / 2, height / 2 + 30, mPaintHour);

        canvas.restore();

 

        float secDegree = sec/60f*360;//得到秒针旋转的角度

        canvas.save();

        canvas.rotate(secDegree,width/2,height/2);

        canvas.drawLine(width/2,height/2-300,width/2,height/2+40,mPaintSec);

        canvas.restore();

 

    }