CODEWITHSUNDEEP
javaandroid
user1445478
user1445478

Reputation: 13

Why does program stop unexpectedly?

I'm writing a very basic program that aims for the text view to display the phrase "Hello" after a button is pressed on the screen, but cannot figure out why every time I run it, it says that the application has stopped unexpectedly.

This is the program I wrote:

public class EtudeActivityActivity extends Activity{
  TextView tvResponse;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    final TextView tvResponse = (TextView)  findViewById (R.id.tvResponse);
  }


  public void updateTV(View v) {
    tvResponse.setText("Hello");
  }
}

Also, I inserted an android:onClick = "updateTV" into my main.xml file for the button.

Thanks for any help!

Upvotes: 1

Views: 193

Answers (2)

Attila
Attila

Reputation: 28762

It is because you don't set the tvResponse member variable. Instead you set a new local variable by the same name. So when you call setText(), you are accessing an invalid reference

You need to change 

final TextView tvResponse = (TextView)  findViewById (R.id.tvResponse);

to 

tvResponse = (TextView)  findViewById (R.id.tvResponse);

to set the member variable, so it has a valid reference later on (when updateTV() is called)

Upvotes: 3

Jon Skeet
Jon Skeet

Reputation: 1500535

I suspect you've got an instance variable called tvResponse which you haven't shown us - that's what the updateTV method will refer to. That's entirely separate from the local tvResponse variable you've declared inside onCreate. I suspect that if you change the last line of onCreate from a local variable declaration to a simple assignment to the tvResponse variable, it may work. Otherwise, if nothing is assigning a value to the instance tvResponse variable, it will have the default value of null, causing a NullPointerException in updateTV.

Upvotes: 1

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