前言

自定义 view 总是绕不开onDraw，而onDraw则少不了Paint与Canvas，这里我们就说说这个。

• 【Android自定义View】目录

Paint

主要的方法：

paint.setColor(Color.RED); //设置画笔颜色
paint.setAntiAlias(true);//抗锯齿功能
paint.setStyle(Style.FILL);//设置填充样式
paint.setStrokeWidth(30);//设置画笔宽度
paint.setTextSize();//设置字体大小

• setStyle 主要有FILL、STROKE、FILL_AND_STROKE

我们来看看效果

        Paint paint = new Paint();
        paint.setColor(Color.RED);
        paint.setStrokeWidth(10);
        paint.setStyle(Paint.Style.FILL);
        canvas.drawCircle(200, 300, 100, paint);
        paint.setStyle(Paint.Style.STROKE);
        canvas.drawCircle(500, 300, 100, paint);
        paint.setStyle(Paint.Style.FILL_AND_STROKE);
        canvas.drawCircle(800, 300, 100, paint);

image.png

FILL和FILL_AND_STROKE 貌似是一样的？我们将strokeWidth设置为100

image.png

Canvas

• 画直线

drawLine(float startX, float startY, float stopX, float stopY,Paint paint)

         paint.setColor(Color.RED);
         canvas.drawLine(100, 100, 200, 300, paint);

drawLines(float[] pts, Paint paint)
其中，pts 长度必须是 4个倍数

        paint.setColor(Color.BLACK);
        float[] pts = {50, 50, 150, 50,
                150, 50, 150, 150,
                150, 150, 250, 150,
                250, 150, 250, 250};
        canvas.drawLines(pts, paint);

需要注意的是，100,150 为第1个点，300,250为第2个点，第1、2个点连线，3、4个点连线

image.png

drawLines(float[] pts, int offset, int count,Paint paint)
offset表示起始位置
count表示从起始位置画多少个点，必须是4个倍数

        float[] pts = {50, 50, 150, 50,
                150, 50, 150, 150,
                150, 150, 250, 150,
                250, 150, 250, 250};
        paint.setColor(Color.BLACK);
        canvas.drawLines(pts, 0, 16, paint);

即和第二步中效果一致，我们修改offset为 4，count 为 12，效果为下图

image.png

• 画矩形

drawRect (float left, float top, float right, float bottom, Paint paint)

canvas.drawRect(100, 200, 400, 800, paint);

其代表的坐标点如下图所示

image.png

drawRect (RectF rect, Paint paint)
drawRect (Rect r, Paint paint)
这2个其实是一样的，left、top、right、bottom和第1个是一致的

    public Rect(int left, int top, int right, int bottom) {
        this.left = left;
        this.top = top;
        this.right = right;
        this.bottom = bottom;
    }

    public RectF(float left, float top, float right, float bottom) {
        this.left = left;
        this.top = top;
        this.right = right;
        this.bottom = bottom;
    }

• 圆角矩形

drawRoundRect(RectF rect, float rx, float ry, Paint paint)
其中，rx代表X轴圆角半径，ry代表Y轴圆角半径

        RectF rectF = new RectF(100, 200, 400, 800);
        canvas.drawRoundRect(rectF, 100, 200, paint);

image.png

drawRoundRect(float left, float top, float right, float bottom, float rx, float ry,Paint paint)
同矩形，rx、ry同方法1

• 圆形

drawCircle(float cx, float cy, float radius, Paint paint)
其中，cx为圆心X轴坐标，cy为圆心Y轴坐标，radius为半径

 canvas.drawCircle(100, 200, 50, paint);

image.png

• 椭圆
  drawOval(RectF oval, Paint paint)
drawOval(float left, float top, float right, float bottom, Paint paint)
  同矩形

        RectF rectF = new RectF(100, 200, 400, 800);
        canvas.drawOval(rectF, paint);

image.png

• 弧线

drawArc(RectF oval, float startAngle, float sweepAngle, boolean useCenter,Paint paint)
drawArc(float left, float top, float right, float bottom, float startAngle, float sweepAngle, boolean useCenter, Paint paint)

startAngle 弧开始的角度，以X轴正方向为0度
sweepAngle 弧持续的角度
useCenter 是否有弧的两边，true 闭合的，false 非闭合的

        paint.setStyle(Paint.Style.STROKE);

        RectF rect = new RectF(50, 100, 200, 400);
        canvas.drawArc(rect, 0, 90, true, paint);

        
        RectF rectF = new RectF(100, 200, 400, 800);
        canvas.drawArc(rectF, 0, 90, false, paint);

image.png

• 示例
  这里就不贴代码了，主要用的画线、矩形和圆，再加上一些位置计算

  
  
  image.png

参考资料：自定义控件之绘图篇（一）：概述及基本几何图形绘制