自定义绘制View

Paint（画笔）

Canvas（画布）

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), anda paint (to describe the colors and styles for the drawing).

1. rotate(float degrees,float px,float py)//对canvas执行旋转变换
2. scale(float sx,float sy)//对canvas执行缩放
3. skew(float sx,float sy)//对canvas执行倾斜变换
4. translate(float dx,float dy)//移动canvas，向右dx,向下dy
5. //
6. setBitmap(Bitmap bitmap)

Path（绘画路径）

预先在View上将N个点连成一条“路径”，然后调用Canvas的drawPath(path,paint)即可沿着路径绘制图形

1. //Path
2. moveTo(float x,float y)//Set the beginning of the next contour to the point (x,y).
3. lineTo(float x,float y)//Add a line from the last point to the specified point (x,y).
4.  
5. //canvas
6. drawTextOnPath(String text, Path path, float hOffset, float vOffset, Paint paint)//hOffset水平偏移 vOffset垂直偏移

Android还为路径绘制提供了PathEffect来定义绘制效果,PathEffect包含如下子类：

ComposePathEffect    CornerPathEffect    DashPathEffect    DiscretePathEffect    PathDashPathEffect    SumPathEffect

1. Paint paint =newPaint();
2. paint.setPathEffect(PathEffect effect);
3.  

实例：采用双缓冲实现画图板

1. publicclassDrawView extends View
2. {
3.     // 定义记录前一个拖动事件发生点的坐标
4.     float preX;
5.     float preY;
6.     privatePath path;
7.     publicPaint paint = null;
8.     // 定义一个内存中的图片，该图片将作为缓冲区
9.     Bitmap cacheBitmap = null;
10.     // 定义cacheBitmap上的Canvas对象
11.     Canvas cacheCanvas = null;
12.  
13.     publicDrawView(Context context,int width ,int height)
14.     {
15.         super(context);
16.         // 创建一个与该View相同大小的缓存区
17.         cacheBitmap =Bitmap.createBitmap(width, height,
18.             Bitmap.Config.ARGB_8888);
19.         cacheCanvas =newCanvas();
20.         path =newPath();
21.         // 设置cacheCanvas将会绘制到内存中的cacheBitmap上
22.         cacheCanvas.setBitmap(cacheBitmap);
23.  
24.         // 设置画笔的颜色
25.         paint =newPaint(Paint.DITHER_FLAG);
26.         paint.setColor(Color.RED);
27.         // 设置画笔风格
28.         paint.setStyle(Paint.Style.STROKE);
29.         paint.setStrokeWidth(1);
30.         // 反锯齿
31.         paint.setAntiAlias(true);
32.         paint.setDither(true);
33.     }
34.  
35.     @Override
36.     public boolean onTouchEvent(MotionEvent event)
37.     {
38.         // 获取拖动事件的发生位置
39.         float x = event.getX();
40.         float y = event.getY();
41.         switch(event.getAction())
42.         {
43.             caseMotionEvent.ACTION_DOWN:
44.                 // 从前一个点绘制到当前点之后，把当前点定义成下次绘制的前一个点
45.                 path.moveTo(x, y);
46.                 preX = x;
47.                 preY = y;
48.                 break;
49.             caseMotionEvent.ACTION_MOVE:
50.                 // 从前一个点绘制到当前点之后，把当前点定义成下次绘制的前一个点
51.                 path.quadTo(preX, preY, x, y);
52.                 preX = x;
53.                 preY = y;
54.                 break;
55.             caseMotionEvent.ACTION_UP:
56.                 cacheCanvas.drawPath(path, paint);// ①
57.                 path.reset();
58.                 break;
59.         }
60.         invalidate();
61.         // 返回true表明处理方法已经处理该事件
62.         returntrue;
63.     }
64.     @Override
65.     publicvoid onDraw(Canvas canvas)
66.     {
67.         Paint bmpPaint =newPaint();
68.         // 将cacheBitmap绘制到该View组件上
69.         canvas.drawBitmap(cacheBitmap,0,0, bmpPaint);// ②
70.         // 沿着path绘制
71.         canvas.drawPath(path, paint);
72.     }
73. }

整理自：《疯狂Android讲义》

来自为知笔记(Wiz)