android - 关于Android Drawable的概念

Question

如何理解Canvas、Drawable、Bitmap、Paint类的概念？他们之间是什么关系？

有人可以给我举个例子吗？

非常感谢。

Answer 1

来自Canvas class文档:

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 the drawing).

所以你需要 4 个组件来绘制一些东西。

1. 位图
2. Canvas
3. 可绘制
4. 画画

假设您想在可绘制文件夹中的背景图片上画一个圆圈。

Canvas canvas;
Bitmap mBG;
Paint mPaint = new mPaint();

mBG = BitmapFactory.decodeResource(res, R.drawable.apple);  //Return a bitmap from the image from drawable folder
Canvas.drawBitmap(mBG, 0,0, null);     //Draw the bitmap

mPaint.setColor(Color.BLACK);          //Set paint to BLACK color
Canvas.drawCircle(100,100,30, mPaint); //Draw circle at coordinate x:100,y:100, radius 30 with the paint defined