Question

I have extended the ImageView class in a class called DialButton2 (dont worry about the name of the class, its irrelevant). All the DialButton2 class does is show an arbitrary image located in the drawable folder.

package com.com.com;

import android.content.Context;
import android.widget.ImageView;
import android.util.AttributeSet;

public class DialButton2 extends ImageView{

    public DialButton2(Context context) {
        super(context);
        this.setImageResource(R.drawable.dialpad);
    }

    public DialButton2(Context context, AttributeSet attrs){
        super(context, attrs);
        this.setImageResource(R.drawable.dialpad);
    }

}

In the XML file for the main activity in my app I specify that a DialButton2 object should be displayed. I give it the id “button1”.

<?xml version="1.0" encoding="utf-8"?>
<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:stretchColumns="1"
    >
   <TableRow
    android:layout_weight="1">
         <DialButton
        android:id="@+id/button1"
        android:src="@drawable/dialpad"
        android:layout_weight="1"
        />

Dont worry about the rest of the XML-file, its irrelevant.

My problem is that when I try to instantiate a reference to the button in code, eclipse tells me I have to cast it to ImageView. Why is this?

package com.com.com;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.Window;

public class Android3 extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.maintable);

        /*
         * The instantiating below gives an error saying I have to cast to ImageView.
         */

        DialButton2 button1 = findViewById(R.id.button1);
    }
}

Answer 1

You have to cast to DialButton2

    DialButton2 button1 = (DialButton2) findViewById(R.id.button1);

findViewById() returns a View, you have to cast it before you can use it as a DialButton2.