不幸的是app已经停止工作

Question

I am new to android application development. I was doing this tutorial app.It's a very simple one. It adds one and subtracts one from the counter.When I run it in the emulator ,it says "Unfortunately tutorial has stopped working." There are no errors in the code. The API level is 17. Please help me out.

Code for java:

public class Startingpoint extends Activity {
  int counter=0;   
  Button add,subtract; 
  TextView display; 

  @Override    
  protected void onCreate(Bundle savedInstanceState) {    
    super.onCreate(savedInstanceState);    
    setContentView(R.layout.startingpoint);    
    add = (Button) findViewById(R.id.bAdd);    
    subtract= (Button) findViewById(R.id.bSubtract);   
    display= (Button) findViewById(R.id.text);    
    add.setOnClickListener(new View.OnClickListener() {

      @Override   
      public void onClick(View v) {   
        counter++;  
        display.setText("The total is " + counter);   
      }   
    });   

    subtract.setOnClickListener(new View.OnClickListener() {
      @Override 
      public void onClick(View v) {
        counter--;
        display.setText("The total is " + counter);
      }

    });
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.startingpoint, menu);
    return true;
  }
}

Layout code in xml :

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

    <TextView android:id="@+id/text"    
              android:layout_width="wrap_content"   
              android:layout_height="wrap_content"
              android:text="Your total is 0"
              android:textSize="35dp"
              android:layout_gravity="center"
              android:gravity="center"/>

    <Button   android:layout_width="250dp"
              android:layout_height="wrap_content"
              android:text="Add One" 
              android:layout_gravity="center" 
              android:textSize="25dp"
              android:id="@+id/bAdd"/>

     <Button  android:layout_width="250dp"
              android:layout_height="wrap_content"
              android:text="Subtract One" 
              android:layout_gravity="center" 
              android:textSize="25dp"
              android:id="@+id/bSubtract"/>
</LinearLayout>

Here is the logcat :

03-02 02:45:10.730: D/AndroidRuntime(780): Shutting down VM
03-02 02:45:10.730: W/dalvikvm(780): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
03-02 02:45:10.750: E/AndroidRuntime(780): FATAL EXCEPTION: main
03-02 02:45:10.750: E/AndroidRuntime(780): java.lang.RuntimeException: Unable to start activity ComponentInfo{tutorial.example.tutorial/tutorial.example.tutorial.Startingpoint}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.os.Looper.loop(Looper.java:137)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.main(ActivityThread.java:5041)
03-02 02:45:10.750: E/AndroidRuntime(780):  at java.lang.reflect.Method.invokeNative(Native Method)
03-02 02:45:10.750: E/AndroidRuntime(780):  at java.lang.reflect.Method.invoke(Method.java:511)
03-02 02:45:10.750: E/AndroidRuntime(780):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-02 02:45:10.750: E/AndroidRuntime(780):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-02 02:45:10.750: E/AndroidRuntime(780):  at dalvik.system.NativeStart.main(Native Method)
03-02 02:45:10.750: E/AndroidRuntime(780): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
03-02 02:45:10.750: E/AndroidRuntime(780):  at tutorial.example.tutorial.Startingpoint.onCreate(Startingpoint.java:22)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.Activity.performCreate(Activity.java:5104)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
03-02 02:45:10.750: E/AndroidRuntime(780):  ... 11 more

Answer 1

display= (Button) findViewById(R.id.text);

should be

display= (TextView) findViewById(R.id.text);

Since display is supposed to reference a TextView instance, but you're explictly casting into a Button , and these are not compatible types.

Answer 2

As you got the answer from AC this time, but for next time in android application development a important suggestion:

Always see the logcat for error, and see the "Caused by:" tag, It specifies what was the cause of the problem with sufficient detail, Also see the line no that caused that error. And try to find what can be wrong with that line of code.

For example: in your logcat it is showing-

Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button 
at tutorial.example.tutorial.Startingpoint.onCreate(Startingpoint.java:22)

So you can try to read the log, and you will understand that in your file Startingpoint.java at line 22 which is located in onCreate method the error is android.widget.TextView cannot be cast to android.widget.Button . So you can easily remove your errors without any help. Hope that helps not only you current problem but prevented your future time and efforts.