有些情況需要將同一類型映射到不同的類實現，還是使用繪圖的例子.
IShape, Rectangle, MyRectangle, MySquare,有如下繼承關系：
我們可能需要將IShape 同時映射到MyRectangle 和MySquare ，這時可以使用Binding Annotation 來實現。 這時使用類型和annotation (標註）可以唯一確定一個Binding。Type 和annotation 對稱為Key（鍵）。
為瞭同時使用MyRectangle和MySequare，我們定義兩個annotation，如下
[java] import com.google.inject.BindingAnnotation;
import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
…
@BindingAnnotation
@Target({ FIELD, PARAMETER, METHOD })
@Retention(RUNTIME)
public @interface Rectangle {
}
…
@BindingAnnotation
@Target({ FIELD, PARAMETER, METHOD })
@Retention(RUNTIME)
public @interface Square {
}
import com.google.inject.BindingAnnotation;
import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
…
@BindingAnnotation
@Target({ FIELD, PARAMETER, METHOD })
@Retention(RUNTIME)
public @interface Rectangle {
}
…
@BindingAnnotation
@Target({ FIELD, PARAMETER, METHOD })
@Retention(RUNTIME)
public @interface Square {
}
定義瞭兩個標註 @Rectangle, @Square, 至於@BindingAnnotation，@Target，@Retention你並不需要詳細瞭解，有興趣的可以參見Java Annotation tutorial .
簡單的說明如下：
@BindingAnnotation 通知這是一個Binding Annotation，如果將多個個標註應用到同一個元素時，Guice會報錯。
@Target({FIELD, PARAMETER, METHOD}) 表示這個標註可以應用到類成員變量，函數的參數或時方法。
@Retention(RUNTIME) 表示這個標註在程序運行時可以使用Reflection讀取。
創建一個BindingAnnotationsDemo 用來繪制兩個圖形：
[java] public class BindingAnnotationsDemo extends Graphics2DActivity{
@Inject @Rectangle IShape shape1;
@Inject @Square IShape shape2;
protected void drawImage(){
/**
* The semi-opaque blue color in
* the ARGB space (alpha is 0x78)
*/
Color blueColor = new Color(0x780000ff,true);
/**
* The semi-opaque green color in the ARGB space (alpha is 0x78)
*/
Color greenColor = new Color(0x7800ff00,true);
graphics2D.clear(Color.WHITE);
graphics2D.Reset();
SolidBrush brush=new SolidBrush(blueColor);
graphics2D.fill(brush,shape1);
AffineTransform at = new AffineTransform();
at.translate(20, 20);
graphics2D.setAffineTransform(at);
brush=new SolidBrush(greenColor);
graphics2D.fill(brush,shape2);
}
}
public class BindingAnnotationsDemo extends Graphics2DActivity{
@Inject @Rectangle IShape shape1;
@Inject @Square IShape shape2;
protected void drawImage(){
/**
* The semi-opaque blue color in
* the ARGB space (alpha is 0x78)
*/
Color blueColor = new Color(0x780000ff,true);
/**
* The semi-opaque green color in the ARGB space (alpha is 0x78)
*/
Color greenColor = new Color(0x7800ff00,true);
graphics2D.clear(Color.WHITE);
graphics2D.Reset();
SolidBrush brush=new SolidBrush(blueColor);
graphics2D.fill(brush,shape1);
AffineTransform at = new AffineTransform();
at.translate(20, 20);
graphics2D.setAffineTransform(at);
brush=new SolidBrush(greenColor);
graphics2D.fill(brush,shape2);
}
}
使用標註將shape1 綁定到MyRectangle, shape2綁定到MySquare，對應的Module 定義如下：
[java] public class Graphics2DModule extends AbstractAndroidModule{
@Override
protected void configure() {
bind(IShape.class)
.annotatedWith(Rectangle.class)
.to(MyRectangle.class);
bind(IShape.class)
.annotatedWith(Square.class)
.to(MySquare.class);
}
}
Inject 可以應用到Field (成員變量）,Parameter (參數）或Method(方法），前面的例子都是應用到Field上，如果應用到參數可以有如下形式：
[java] @Inject
public IShape getShape(@Rectangle IShape shape){
…
}
@Inject
public IShape getShape(@Rectangle IShape shape){
…
}
如果你不想自定義Annotation，可以使用Guice自帶的@Name標註來解決同一類型綁定到不同實現的問題。
修改上面代碼：
[java] //@Inject @Rectangle IShape shape1;
//@Inject @Square IShape shape2;
@Inject @Named("Rectangle") IShape shape1;
@Inject @Named("Square") IShape shape2;
//@Inject @Rectangle IShape shape1;
//@Inject @Square IShape shape2;
@Inject @Named("Rectangle") IShape shape1;
@Inject @Named("Square") IShape shape2;
修改綁定如下：
[java] view plaincopyprint? //bind(IShape.class)
//.annotatedWith(Rectangle.class)
//.to(MyRectangle.class);
//bind(IShape.class)
//.annotatedWith(Square.class)
//.to(MySquare.class);
bind(IShape.class)
.annotatedWith(Names.named("Rectangle"))
.to(MyRectangle.class);
bind(IShape.class)
.annotatedWith(Names.named("Square"))
.to(MySquare.class);
//bind(IShape.class)
//.annotatedWith(Rectangle.class)
//.to(MyRectangle.class);
//bind(IShape.class)
//.annotatedWith(Square.class)
//.to(MySquare.class);
bind(IShape.class)
.annotatedWith(Names.named("Rectangle"))
.to(MyRectangle.class);
bind(IShape.class)
.annotatedWith(Names.named("Square"))
.to(MySquare.class);
這種方法簡單，但編譯器無法檢測字符串，比如將”Square”錯寫為”Sqare”，編譯器無法查出這個錯誤，此時到運行時才可能發現 shape2 無法註入，因此建議盡量少用Named.
本例下載：http://up.aiwalls.com/2012/0504/20120504095233906.zip
摘自 引路蜂移動軟件