Android RoboGuice使用指南(4):Linked Bindings

Roboguice 中最常用的一种绑定为Linked Bindings，将某个类型映射到其实现。这里我们使用引路蜂二维图形库中的类为例。
使用下面几个类IShape, Rectangle, MyRectangle, MySquare, 其继承关系如下图所示：


下面代码将IShape 映射到MyRectangle



public class Graphics2DModule extends AbstractAndroidModule{
  
@Override
protected void configure() {
  
bind(IShape.class).to(MyRectangle.class);
  
}
}
public class Graphics2DModule extends AbstractAndroidModule{

@Override
protected void configure() {

bind(IShape.class).to(MyRectangle.class);

}
}
此时，如果使用injector.getInstance(IShape.class) 或是injector 碰到依赖于IShape地方时,它将使用MyRectangle。可以将类型映射到它任意子类或是实现了该类型接口的所有类。也可以将一个实类（非接口）映射到其子类，如
bind(MyRectangle.class).to(MySquare.class);
下面例子使用@Inject 应用IShape.
[java] public class LinkedBindingsDemo extends Graphics2DActivity{
  
@Inject IShape  shape;
  
protected void drawImage(){
  
/**
* The semi-opaque blue color in
* the ARGB space (alpha is 0x78)
*/
Color blueColor = new Color(0x780000ff,true);
/**
* The semi-opaque yellow color in the
* ARGB space ( alpha is 0x78)
*/
Color yellowColor = new Color(0x78ffff00,true);
  
/**
* The dash array
*/
int dashArray[] = { 20 ,8 };
graphics2D.clear(Color.WHITE);
graphics2D.Reset();
Pen pen=new Pen(yellowColor,10,Pen.CAP_BUTT,
Pen.JOIN_MITER,dashArray,0);
SolidBrush brush=new SolidBrush(blueColor);
graphics2D.setPenAndBrush(pen,brush);
graphics2D.fill(null,shape);
graphics2D.draw(null,shape);
  
}
  
}
public class LinkedBindingsDemo extends Graphics2DActivity{

@Inject IShape  shape;

protected void drawImage(){

/**
* The semi-opaque blue color in
* the ARGB space (alpha is 0x78)
*/
Color blueColor = new Color(0x780000ff,true);
/**
* The semi-opaque yellow color in the
* ARGB space ( alpha is 0x78)
*/
Color yellowColor = new Color(0x78ffff00,true);

/**
* The dash array
*/
int dashArray[] = { 20 ,8 };
graphics2D.clear(Color.WHITE);
graphics2D.Reset();
Pen pen=new Pen(yellowColor,10,Pen.CAP_BUTT,
Pen.JOIN_MITER,dashArray,0);
SolidBrush brush=new SolidBrush(blueColor);
graphics2D.setPenAndBrush(pen,brush);
graphics2D.fill(null,shape);
graphics2D.draw(null,shape);

}

}
使用bind(IShape.class).to(MyRectangle.class)，为了简化问题，这里定义了MyRectangle和MySquare都带有一个不带参数的构造函数，注入具有带参数的构造函数类用法在后面有介绍。
[java] public class MyRectangle extends Rectangle{
public MyRectangle(){
super(50,50,100,120);
}
  
public MyRectangle(int width, int height){
super(50,50,width,height);
}
}
...
public class MySquare extends MyRectangle {
  
public MySquare(){
super(100,100);
}
  
public MySquare(int width){
super(width,width);
}
  
}





Linked bindings 允许链接，例如

[java] public class Graphics2DModule extends AbstractAndroidModule{
  
@Override
protected void configure() {
bind(IShape.class).to(MyRectangle.class);
bind(MyRectangle.class).to(MySquare.class);
  
}
}
public class Graphics2DModule extends AbstractAndroidModule{

@Override
protected void configure() {
bind(IShape.class).to(MyRectangle.class);
bind(MyRectangle.class).to(MySquare.class);

}
}

此时当需要IShape 时，Injector返回MySquare 的实例, IShape->MyRectangle->MySquare