Android Roboguice Use Guide (6) Instance bindings

In the previous example, the Android Roboguice use Guide (4): Linked bindings for simplicity, defining MyRectangle and MySQUARE defines a constructor that takes no parameters, such as MyRectangle, as follows:

public class MyRectangle extends rectangle{public 

    
 myrectangle () {
 super (50,50,100,120);
 }
 public myrectangle (int width, int height) {
 super (50,50,width,height);
 }

You can actually do without this constructor without arguments, you can use Instance bindings, Instance bindings can bind a type to a particular instance object, typically to a type that does not depend on other classes, such as a variety of basic types, such as:

Bind

(String.class)     
 . Annotatedwith (names.named ("JDBC URL")     
 . ToInstance ("jdbc:mysql://localhost/ Pizza ");     
Bind (Integer.class)     
 . Annotatedwith (names.named ("Login timeout Seconds"))     
 . ToInstance (10);

The definitions for modifying MyRectangle and MySQUARE are as follows:

public class MySQUARE extends MyRectangle {     
 @Inject public 
 mysquare (@Named ("width") int width) {     
 super ( width,width);     
 }     
...     
The public class MyRectangle extends rectangle{     
          
 @Inject 
 the public MyRectangle (@Named ("width") int width,     
 @Named ("height") int height) {     
 super (50,50,width,height);     
 }     
}

With a parameterless constructor, you can bind the int type labeled @named ("width") to 100, adding the following bindings:

Bind (Integer.class)     
 . Annotatedwith (names.named ("width"))     
 . toinstance (MB);     
Bind (Integer.class)     
 . Annotatedwith (names.named ("height"))     
 . ToInstance (120);

To run this example, you can get the same result as the previous example. When using injector to construct a MyRectangle instance, injector automatically selects the constructor with the parameter, using 100,120 as the width and height injection parameters, returns a MyRectangle object to the place that needs to be referenced.

Although you can use instance bindings to map a type to a class instance of a complex type, Roboguice does not recommend applying instance bindings to instances of complex types, because it slows down the application startup.

The correct approach is to use the @Provides method, which is described below.

Note: the example in Guicedemo does not use a list method to display all the examples, and if you need to run the required samples, you can set up the launch activity through run Configuration->:

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