从Android绘制View小例子中深入理解自定义View _android绘制

业无高卑志当坚，男儿有求安得闲？这篇文章主要讲述从Android绘制View小例子中深入理解自定义View相关的知识，希望能为你提供帮助。
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