Question

I have defined a class XX like this:

   public class XX extends RelativeLayout {
    protected static final boolean DEBUG = true;

    public XX(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
    }

    public XX(Context context, AttributeSet attrs) {
    super(context, attrs);
    if (DEBUG)
        Log.i(this.getClass().getSimpleName(), " ->2"
            + Thread.currentThread().getStackTrace()[2].getMethodName());
    //getAttributes(context, attrs);

    }

    public XX(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    if (DEBUG)
        Log.i(this.getClass().getSimpleName(), " ->3"
            + Thread.currentThread().getStackTrace()[2].getMethodName());
    //getAttributes(context, attrs);

    }

}

and in my code I write:

RelativeLayout v = (RelativeLayout) this.findViewById(R.id.switch_TCMyTB);
XX x = (XX) v;  //<----- crashes here

but it crashes with the assignment. I assume the because XX extends View I can just assign the view (RelativeLayout) to an XX object.

But it crashes. What is wrong with the assignment?

EDIT:

I changed extends View to extends RelativeLayout. Also changed View v to RelativeLayout v.
But I still get a classCastException..???? Why?

While

RelativeLayout r = (RelativeLayout) v; 

certainly works fine.

Answer 1

Since I’m not completely familiar with custom components, I just tried to make an example.
I can’t answer your question as to why it wont work. If my example won’t run for you, you will need to provide a logcat.

I create a custom class:

public class TestLayout extends RelativeLayout {

    public TestLayout(Context context) {
        super(context);

    }

    public TestLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

    }

    public TestLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }
}

This class is in the package com.test.cc

In an XML layout I use

    <com.test.cc.TestLayout 
    android:layout_width="10dip"
    android:layout_height="10dip"
    android:id="@+id/testLayout"    
    />

In this example layout.. TestLayout is a child of a LinearLayout.
Add xmlns:android="http://schemas.android.com/apk/res/android" if its the highest level component in an xml layout.

Then in the activity:

//Called in onCreate mthod of an activity.    
setContentView(R.layout.test); //make sure you call this first
TestLayout l = (TestLayout)findViewById(R.id.testLayout);

This runs fine for me.

This was tested on a 2.2 and 3.2 device.

So make sure you call setContentView(…) first and then create an object of the layout.
Also make sure in the xml deffinition the package is right. Although if this was wrong you would get an class not foudn exception

EDIT||

I tried running this:

RelativeLayout l = (RelativeLayout)findViewById(R.id.testLayout);
TestLayout tl = (TestLayout)l;

And it also runs fine without any exceptions. So I assume the problem lies elsewhere. Maybe package name errors or something.