Question

I am new to Android. I am trying to build this tiny app however every time I add the code in bold:

d = (Button) findViewById (R.id.tvDis);

the app crashes and if I remove this line, everything works fine. I am runing this on android 2.2 api 8 version and nexus s emulator.

package com.maximusstudios.numtowords;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class MainActivity extends Activity {
/**Called when the activity is first created.*/
    int counter;
    Button add, sub;
    TextView d;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        counter = 0;
        add = (Button) findViewById (R.id.bAdd);
        **d = (Button) findViewById (R.id.tvDis);**
        sub = (Button) findViewById(R.id.bSub);
        add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                counter++;

            }
        });
sub.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                counter--;
            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

XML CODE:

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" 
        android:text="Your Total is 0"
        android:textSize="20dp"
        android:layout_gravity="center"
        android:gravity="center"
        android:id="@+id/tvDis"

         />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add one"
        android:layout_gravity="center"
        android:textSize="20dp"
        android:id="@+id/bAdd"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add one"
        android:layout_gravity="center"
        android:textSize="20dp"
        android:id="@+id/bSub"
        />

</LinearLayout>

Error list:

02-10 18:00:21.452: D/AndroidRuntime(910): Shutting down VM
02-10 18:00:21.452: W/dalvikvm(910): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
02-10 18:00:21.472: E/AndroidRuntime(910): FATAL EXCEPTION: main
02-10 18:00:21.472: E/AndroidRuntime(910): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.maximusstudios.numtowords/com.maximusstudios.numtowords.MainActivity}: java.lang.ClassCastException: android.widget.TextView
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.os.Handler.dispatchMessage(Handler.java:99)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.os.Looper.loop(Looper.java:123)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.ActivityThread.main(ActivityThread.java:4627)
02-10 18:00:21.472: E/AndroidRuntime(910):  at java.lang.reflect.Method.invokeNative(Native Method)
02-10 18:00:21.472: E/AndroidRuntime(910):  at java.lang.reflect.Method.invoke(Method.java:521)
02-10 18:00:21.472: E/AndroidRuntime(910):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
02-10 18:00:21.472: E/AndroidRuntime(910):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
02-10 18:00:21.472: E/AndroidRuntime(910):  at dalvik.system.NativeStart.main(Native Method)
02-10 18:00:21.472: E/AndroidRuntime(910): Caused by: java.lang.ClassCastException: android.widget.TextView
02-10 18:00:21.472: E/AndroidRuntime(910):  at com.maximusstudios.numtowords.MainActivity.onCreate(MainActivity.java:23)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-10 18:00:21.472: E/AndroidRuntime(910):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
02-10 18:00:21.472: E/AndroidRuntime(910):  ... 11 more

Answer 1

Change to

d = (TextView) findViewById (R.id.tvDis);

Your casting was wrong. With your code, when you do (Button), you are trying to cast the TextView that is returned by findViewById() into a Button, which doesn’t work due to them being incompatible types.