从Android绘制View小例子中深入理解自定义View

平时开发界面时，Android系统为我们提供了各种各样的View组件，TextView、ImageView、Button、LinearLayout、ScrollView、ListView等等，这些也基本满足了平时的开发要求。有时候开发也会遇到比较刁钻的需求，自定义View多多少少就会用到。

彻底搞懂自定义View并不容易，因为牵扯到尺寸计算、Location（定位）、Canvas、矩阵计算等等，内容还是挺多的。记得刚入门Android时很快搞定了一个自定义View，后面才发现这还远远不够。

1，首先要配置View的尺寸和位置

1）比如实现一个正方形的View，保持高度和宽度一致

    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        int widthSize = MeasureSpec.getSize(widthMeasureSpec);        heightMeasureSpec = MeasureSpec.makeMeasureSpec(widthSize, MeasureSpec.EXACTLY);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);    }

2）配置View在父View中的位置,使用onLayout

    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        super.onLayout(changed, left, top, right, bottom);    }

2,在绘制内容前，你要准备好画笔

        prPaint = new Paint();        //防锯齿        prPaint.setAntiAlias(true);        //防抖动        prPaint.setDither(true);        prPaint.setStrokeCap(Paint.Cap.ROUND);        prPaint.setStyle(Paint.Style.STROKE);        prPaint.setStrokeWidth(PR_STROKE_WIDTH);        dot = new Path();        //指定顺时针方向(CW)        dot.addCircle(0, 0, DOTTED_LINE_WIDTH / 2, Path.Direction.CW);        dotPaint = new Paint();        dotPaint.setAntiAlias(true);        dotPaint.setDither(true);        dotPaint.setStyle(Paint.Style.STROKE);        dotPaint.setColor(Color.WHITE);        innerCircle = new Paint();        innerCircle.setAntiAlias(true);        innerCircle.setDither(true);        innerCircle.setStyle(Paint.Style.STROKE);        innerCircle.setStrokeWidth(INNER_LINE);        innerCircle.setColor(themeColor);        effects_line = new DashPathEffect(new float[]{30, 10}, 1);

3，将内容通过画布绘制出来

    @Override    public void draw(Canvas canvas) {        super.draw(canvas);        dotDrawRect.set(dotRect);        final float centerX = dotDrawRect.centerX();        final float centerY = dotDrawRect.centerY();        float radius = dotDrawRect.width() / 2;        initPathEffect();        dotPaint.setPathEffect(effects1);        canvas.drawCircle(centerX, centerY, radius, dotPaint);        radius = radius - DOTTED_LINE_PADDING;        dotPaint.setPathEffect(effects2);        canvas.drawCircle(centerX, centerY, radius, dotPaint);        radius = radius - DOTTED_LINE_PADDING;        dotPaint.setPathEffect(effects3);        canvas.drawCircle(centerX, centerY, radius, dotPaint);        radius = radius - DOTTED_LINE_PADDING;        dotPaint.setPathEffect(effects4);        canvas.drawCircle(centerX, centerY, radius, dotPaint);        radius = radius - DOTTED_LINE_PADDING;        innerCircle.setPathEffect(null);        innerCircle.setColor(Color.WHITE);        canvas.drawCircle(centerX, centerY, radius, innerCircle);        radius = (float) (radius - DOTTED_LINE_PADDING * 1.5);        innerCircle.setPathEffect(effects_line);        innerCircle.setColor(themeColor);        canvas.drawCircle(centerX, centerY, radius, innerCircle);        radius = radius - PR_STROKE_WIDTH / 2 - DOTTED_LINE_PADDING / 2;        if (powInterRadius == 0) {            powInterRadius = Math.pow(radius, 2);        }        //进度条绘制        dotDrawRect.set(centerX - radius, centerY - radius, centerX + radius, centerY + radius);        prPaint.setColor(Color.GRAY);        canvas.drawArc(dotDrawRect, 120, 300, false, prPaint);        prPaint.setColor(Color.WHITE);        canvas.drawArc(dotDrawRect, 120, progress * 3, false, prPaint);    }

4，如果需要和用户交互，还需要处理触摸、点击这些事件（以后再仔细分析）

源码：http://git.oschina.net/hanbingsheshou/SimpleDraw

从哪里跌倒就会从哪里爬起来,让我们一起努力吧