CODEWITHSUNDEEP
javaandroidclassextends
zharik86
zharik86

Reputation: 51

Android: Inner class error

I am developing an application in Android and have a problem. I have two classes A and B. Their code is as below(for example):

public class A extends View {
//declaration of constructors
...
    public class B extends Button {
    //declaration of constructors
    }
}

I try to add in xml the designer a class B, but I receive an error and it adds nothing.

<com.example.myproject.A.B
android:is="@+id/B1"
android:layout_wight="100dp"
android:layout_height="100dp"
.../>

What is the probable error and how to make a class as shown above free of errors in the designer of xml ?

Upvotes: 0

Views: 242

Answers (2)

Michael
Michael

Reputation: 54705

Your code should be like this:

public class A extends View {
//declaration of constructors
...
    public static class B extends Button {
    //declaration of constructors
    }
}

And the layout:

<view class="com.example.myproject.A$B"
    android:id="@+id/B1"
    android:layout_wight="100dp"
    android:layout_height="100dp"
    .../>

The most important thing here is that B is static nested class, not just inner class. You can't instantiate an inner class if you don't have an instance of an outer class, which is A in your case.

Upvotes: 1

user
user

Reputation: 87064

You can't use those classes as creating an instance of B would require a reference to A in the first place. You either make the B class static in A and use:

<view
   class="com.example.myproject.A$B"
   android:is="@+id/B1"
   android:layout_wight="100dp"
   android:layout_height="100dp"
/>

or you rethink your current class hierarchy.

Upvotes: 1

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