canvas, drawable, bitmap之间的关系

In short

Bitmap - is a representation of image in byte form.

Bitmap就是用一个字节数组表示一张图片.

public final class Bitmap implements Parcelable {

    /**
     * Backing buffer for the Bitmap.
     */
    private byte[] mBuffer;
}

Drawable - is an abstraction of anything which can be drawn. (image, gradients, circles, shape, 9 patch, state, layers etc)

Drawable就是可画在屏幕上的任何类型的图形，是一个抽象的代码表示 eg, 图片或是shape.

Canvas - is a place, where you draw. Like real life Canvas. Where you can draw anything.

Canvas 就是一个画布， 可以在上面画任何图形.

canvas.drawRect(leftMargin, 0,
                        leftMargin + mBarDrawWidth, getHeight(), mFillPaint);

canvas.drawLine(lineX, 0, lineX, getHeight(), mStrokePaint);

canvas.drawBitmap(bitmap, null, rectSrc, paint);

-------DONE.------------