Android RoboGuice使用指南(7):@Provides Methods

例说过如果需要构造一些较复杂的类的实例，通常的方法是使用@Provides 方法。这个方法必须定义在模块中(Module)，而且必须使用@Provides 标注，在个方法的返回类型则绑定到这个方法返回的对象实例。

如果这个方法带有binding Annotation 或是@Named(“xxx”)，Guice则将@Provides方法返回的对象绑定到这个annotated 类型。

本例使用@Provides创建三个圆，然后再屏幕上显示出来，图形库的使用可以参见Android简明开发教程十二：引路蜂二维图形库简介及颜色示例 。其实创建圆并不复杂，这里只是用来说明@Provides 方法的用法。

在Graphics2DModule 在添加三个@Provides方法：

[java] @Provides @Named("Circle1") 
IShape provideCircle1(){ 
 return new Ellipse(30,60,80,80); 
} 
  
@Provides @Named("Circle2") 
IShape provideCircle2(){ 
 return new Ellipse(60,30,80,80); 
} 
  
@Provides @Named("Circle3") 
IShape provideCircle3(){ 
 return new Ellipse(90,60,80,80); 
} 
@Provides @Named("Circle1")
IShape provideCircle1(){
 return new Ellipse(30,60,80,80);
}
 
@Provides @Named("Circle2")
IShape provideCircle2(){
 return new Ellipse(60,30,80,80);
}
 
@Provides @Named("Circle3")
IShape provideCircle3(){
 return new Ellipse(90,60,80,80);
}

分别绑定到IShape带有标注@Named(“Circle1″)，@Named(“Circle2″)，@Named(“Circle3″).

创建ProvidesMethodsDemo，有如下代码

[java] public class ProvidesMethodsDemo extends Graphics2DActivity{ 
  
 @Inject @Named("Circle1") IShape circle1; 
 @Inject @Named("Circle2") IShape circle2; 
 @Inject @Named("Circle3") IShape circle3; 
  
 protected void drawImage(){ 
  
 // The solid (full opaque) red color in the ARGB space  
 Color redColor    = new Color(0xffff0000); 
  
 // The semi-opaque green color in the ARGB space (alpha is 0x78)  
 Color greenColor = new Color(0x7800ff00,true); 
  
// 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(); 
 SolidBrush brush=new SolidBrush(redColor); 
 graphics2D.fill(brush,circle1); 
 brush=new SolidBrush(greenColor); 
 graphics2D.fill(brush,circle2); 
 Pen pen=new Pen(yellowColor,10,Pen.CAP_BUTT,Pen.JOIN_MITER,dashArray,0); 
 brush=new SolidBrush(blueColor); 
 graphics2D.setPenAndBrush(pen,brush); 
 graphics2D.fill(null,circle3); 
 graphics2D.draw(null,circle3); 
  
 } 
  
} 
public class ProvidesMethodsDemo extends Graphics2DActivity{
 
 @Inject @Named("Circle1") IShape circle1;
 @Inject @Named("Circle2") IShape circle2;
 @Inject @Named("Circle3") IShape circle3;
 
 protected void drawImage(){
 
 // The solid (full opaque) red color in the ARGB space
 Color redColor    = new Color(0xffff0000);
 
 // The semi-opaque green color in the ARGB space (alpha is 0x78)
 Color greenColor = new Color(0x7800ff00,true);
 
// 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();
 SolidBrush brush=new SolidBrush(redColor);
 graphics2D.fill(brush,circle1);
 brush=new SolidBrush(greenColor);
 graphics2D.fill(brush,circle2);
 Pen pen=new Pen(yellowColor,10,Pen.CAP_BUTT,Pen.JOIN_MITER,dashArray,0);
 brush=new SolidBrush(blueColor);
 graphics2D.setPenAndBrush(pen,brush);
 graphics2D.fill(null,circle3);
 graphics2D.draw(null,circle3);
 
 }
 
}
@Provides方法通常用来创建将复杂的类对象，可以带参数，参数也可以通过注入传入比如：

[java] @Provides @Named("Circle1") 
IShape provideCircle1(@Named("width") int width){ 
 return new Ellipse(30,60,width,width); 
} 






本例下载：../../2012/0504/20120504095832813.zip





摘自 引路蜂移动软件