【自定义控件系列一】android画图类---Canvas浅谈

概要：

本人在目前项目中很多页面都需要自定义控件，所以抽出时间对自定义控件进行系统的复习，并对此发表一下本人的拙见，也方便今后复习。

学习之前先看一下，这次分享最终要做的自定义控件吧，整张图除了中间的文字是TextView 其他的都是画出来的，而且圆指向柱状体顶部的箭头是

通过计算出来位置后画出来的。这个Demo我会在最后一篇文章中进行分享

好其他不多说开始这次的学习之旅吧！！！

Canvas类

首先看一下Canvas类官方说明

The Canvas class holds the "draw" calls. To draw something, you need 4 basic components: A Bitmap to hold the pixels, a Canvas to host
the draw calls (writing into the bitmap), a drawing primitive (e.g. Rect,Path, text, Bitmap), and a paint (to describe the colors and styles for thedrawing).

大致意思：Canvas是一个画布，它具有执行画的动作.

它有4个基本的组件，包括：

一个Bitmap的画布，

一个Canvas类会调用这个Bitmap（把图画在这个Bitmap身上），

一个填充的域 Path、Rect、ovil等（比如矩形，路径，文字，图片等）

一个画笔 Paint（用来定义画出来的控件的颜色，样式等等）

（一）获取Canvas

第一种在所有View的onDraw（Canvas canvas）方法中直接获取

@Override
protected void onDraw(Canvas canvas) {
<span style="white-space:pre"></span>super.onDraw(canvas);
}

第二种直接new一个Canvas

//先得到一个Bitmap对象，通过Canvas的构造函数创建一个Canvas类
Bitmap bitmap = Bitmap.createBitmap(100, 100, Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);

//或者先创建一个Canvas类，通过setBitmap()方法创建一个画布
Canvas canvas = new Canvas();
canvas.setBitmap(bitmap);

第三种调用SurfaceHolder.lockCanvas()，返回一个Canvas对象

（二）Canvas的API

自定义控件完全是自己对API的熟练程度，所以大家对Canvas类的方法一定要熟悉，以便在运用的时候能够灵活的掌握

//获取画布宽高
canvas.getHeight();
canvas.getWidth();

//获取Canvas画布像素密度
canvas.getDensity();

//获取画布过滤器
canvas.getDrawFilter();

//设置Canvas的Matrix矩阵
public void concat(Matrix matrix)

//clip相关的方法主要是对画布Canvas进行裁剪
canvas.clipPath(path_STROKE);
canvas.clipPath(path_STROKE, op);
canvas.clipRect(rect);
canvas.clipRect(rect, op);
canvas.clipRect(left, top, right, bottom);
canvas.clipRect(left, top, right, bottom, op);
canvas.clipRegion(region);
canvas.clipRegion(region, op);

//给Canvas画布填充颜色
canvas.drawARGB(a, r, g, b);
canvas.drawColor(color);
canvas.drawColor(color, mode);

//通过不同参数在Canvas上画位图
canvas.drawBitmap(bitmap, left, top, paint_STROKE);
canvas.drawBitmap(bitmap, matrix, paint_STROKE);
canvas.drawBitmap(bitmap, src, dst, paint_STROKE);
canvas.drawBitmap(bitmap, src, dst, paint_STROKE);
canvas.drawBitmap(colors, offset, stride, x, y, width, height, hasAlpha, paint_STROKE);
canvas.drawBitmapMesh(bitmap, meshWidth, meshHeight, verts, vertOffset, colors, colorOffset, paint_STROKE);

//通过不同的参数在Canvas上画图片
canvas.drawPicture(picture);
canvas.drawPicture(picture, dst);
canvas.drawPicture(picture, dst);

//在Canvas上画圆和椭圆
canvas.drawCircle(cx, cy, radius, paint_STROKE);

//扇形
canvas.drawArc(oval, startAngle, sweepAngle, useCenter, paint_STROKE);

//椭圆
canvas.drawOval(oval, paint_STROKE);

//在Canvas上画线
canvas.drawLine(startX, startY, stopX, stopY, paint_STROKE);
canvas.drawLines(pts, paint_STROKE);
canvas.drawLines(pts, offset, count, paint_STROKE);

//在Canvas画布上画点
canvas.drawPoint(x, y, paint_STROKE);
canvas.drawPoints(pts, paint_STROKE);
canvas.drawPoints(pts, offset, count, paint_STROKE);

//在Canvas画布上画矩形或圆角矩形
canvas.drawRect(r, paint_STROKE);
canvas.drawRect(rect, paint_STROKE);
canvas.drawRoundRect(rect, rx, ry, paint_STROKE);

//利用Canvas在画布上写文字相关Api
canvas.drawPosText(text, pos, paint_STROKE);
canvas.drawPosText(text, index, count, pos, paint_STROKE);

canvas.drawText(text, x, y, paint_STROKE);
canvas.drawText(text, index, count, x, y, paint_STROKE);
canvas.drawText(text, start, end, x, y, paint_STROKE);
canvas.drawText(text, start, end, x, y, paint_STROKE);

canvas.drawTextOnPath(text, path_STROKE, hOffset, vOffset, paint_STROKE);
canvas.drawTextOnPath(text, index, count, path_STROKE, hOffset, vOffset, paint_STROKE);

//绘制顶点(指多边形)
canvas.drawVertices(mode, vertexCount, verts, vertOffset, texs, texOffset, colors, colorOffset, indices, indexOffset, indexCount, paint_STROKE);

//给Canvas设置一个bitmap画布
canvas.setBitmap(bitmap);

//获取画布宽高
canvas.getHeight();
canvas.getWidth();

//获取和设置Canvas画布像素密度
canvas.getDensity();
canvas.setDensity(density);

//获取和设置画布过滤器
canvas.getDrawFilter();
canvas.setDrawFilter(filter);

//获取Canvas上截取的矩形
canvas.getClipBounds();
canvas.getClipBounds(bounds);


//获取Canvas的矩阵
canvas.getMatrix();
canvas.getMatrix(ctm);
canvas.setMatrix(matrix);

//返回此位图绘制画布上允许的最大高度和宽度。试图用一个位图画比这个值高会导致错误。
canvas.getMaximumBitmapHeight();
canvas.getMaximumBitmapWidth();

//返回画布上的私有堆栈状态的矩阵或截图。
canvas.getSaveCount();

//判断此画布使用硬件加速
canvas.isHardwareAccelerated();

//如果当前层引入装置是不透明的返回true
canvas.isOpaque();

//暂时没有用过，不知道怎么用
canvas.quickReject(path_STROKE, type);
canvas.quickReject(rect, type);
canvas.quickReject(left, top, right, bottom, type);

//返回调用save()之前状态，是用来清除所有修改矩阵或裁剪自上次保存状态
canvas.restore();
canvas.restoreToCount(saveCount);

//保存当前画布状态，之后的的 translate,scale,rotate,skew,concat or clipRect,clipPath等都会照常运行
//但调用restore()后，会回复到save之前的Canvas状态
canvas.save();
canvas.save(saveFlags);

//和save()类似，在现在的层上新建一层，调用restore后回复原状态
canvas.saveLayer(bounds, paint_STROKE, saveFlags);
canvas.saveLayer(left, top, right, bottom, paint_STROKE, saveFlags);
canvas.saveLayerAlpha(bounds, alpha, saveFlags);
canvas.saveLayerAlpha(left, top, right, bottom, alpha, saveFlags);

//让画布扭曲
canvas.skew(sx, sy);

//让画布旋转
canvas.rotate(degrees);
canvas.rotate(degrees, px, py);

//让画布缩放
canvas.scale(sx, sy);
canvas.scale(sx, sy, px, py);

//让画布翻转
canvas.translate(dx, dy);