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

补充：移动开发 , Android ,