Drawable简单使用

Android文档这样定义Drawable的：

A Drawable is a general abstraction for "something that can be drawn."
Most
often you will deal with Drawable as the type of resource retrieved for
drawing things to the screen; the Drawable class provides a generic API
for
dealing with an underlying visual resource that may take a variety of
forms.
Unlike a

View

,
a Drawable does not have any facility to
receive events or otherwise interact with the user.

Drawable就是一个可画的对象，其可能是一张位图（BitmapDrawable），也可能是一个图形（ShapeDrawable），还有可能是
一个图层（LayerDrawable），我们根据画图的需求，创建相应的可画对象，就可以将这个可画对象当作一块“画布（Canvas）”，在其上面操作可画对象，并最终将这种可画对象显示在画布上，有点类似于“内存画布“。

下面的一个自定义View显示了ShapeDrawable的一些简单使用方式：

public class TestView extends View {
private ShapeDrawable mShapeDrawable;
public TestView(Context context) {
super(context);

int x = 10, y = 10;
int width = 300, height = 50;

mShapeDrawable = new ShapeDrawable(new OvalShape());
//ShapeDrawable.getPaint():Returns the Paint used to draw the shape
mShapeDrawable.getPaint().setColor(Color.YELLOW);
mShapeDrawable.setBounds(x, y, x+width, y+height);
}

@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);

canvas.drawColor(Color.WHITE);
mShapeDrawable.draw(canvas);
}
}

程序运行效果如下图：