I am doing Android programming and was learning about Intents, when I saw a constructor that, to my C# trained mind, seemed funky. The call was:
Intent myIntent = new Intent(CurrentActivity.this, NextActivity.class);
Both of the parameters are new to me. How is there a static ".this" off of a Class Name? Is this a Java thing or an Android thing? I am assuming that it is the same as just saying "this", since I am in the context of CurrentActivity, but I don't get how the "this" can be called off of the Class name itself. Also. The ".class" looks like it is used for reflection, which I am familiar with in C#, but any insight into this would be welcomed as well.
Thanks.
Source: Tips4all
Usually, you can use only this. But, sometimes this makes reference to an inner class... so, for example:
ReplyDeleteButton button = (Button)findViewById(R.id.ticket_details_sell_ticket);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// it will be wrong to use only "this", because it would
// reference the newly created OnClickListener object
Intent login = new Intent(ClassName.this, Login.class);
startActivityForResult(login, LOGIN_REQUEST);
}
});
The syntax "Classname.this" is for inner classes. If you want to refer to the enclosing instance of type "Outerclass" then you do it as "Outerclass.this".
ReplyDeleteNextActivity.class is simply the Class object that describes class "NextActivity".
One at a time:
ReplyDeleteThe first construct is called a qualified this. The purpose of the syntax is in the case where you are in an inner class (typically an anonymous inner class) and you want to reference the this of the outer class rather than the this of the (anonymous) inner class.
The second construct is called a class literal is the way to reference the Class object that represents that type.
NextActivity.class in java means typeof(NextActivity) in C#
ReplyDeleteClassName.this is used to reference the current instance of an outerclass from an inner class.
ReplyDelete<ClassName>.this
ReplyDeleteis used in nested classes to refer to the current instance of the enclosing class, since the `this' keyword refers to the nest class instance.
public class Siht {
class NestedSiht {
void demoThis() {
System.err.println("this' is an instance of: " +
this.getClass().getName());
System.err.println("Siht.this' is an instance of: " +
Siht.this.getClass().getName());
}
}
void demoThis() {
new java.lang.Object() {
void demoThis() {
System.err.println("`this' is an instance of: " +
this.getClass().getName());
System.err.println("`Siht.this' is an instance of: " +
Siht.this.getClass().getName());
}
}.demoThis();
new NestedSiht().demoThis();
}
public static void main(String [] args) {
new Siht().demoThis();
}
}