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Android Build a Simple Android App Basic Android Programming Adding the OnClick Method

Posted by Jonas Grønbek
Jonas Grønbek
403 Points

''My application has stopped'' code and crash error as comment, please help!

--------- beginning of crash E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.myapplication, PID: 2472 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at com.example.myapplication.FunFactsActivity$1.onClick(FunFactsActivity.java:29) at android.view.View.performClick(View.java:5637) at android.view.View$PerformClick.run(View.java:22429) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) Application terminated.

Jonas Grønbek
Jonas Grønbek
403 Points

public class FunFactsActivity extends AppCompatActivity { // Declare our viewvariables private TextView FactsTextView; private Button mShowFact;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_fun_facts);

    // Assign the views from the layout to the corresponding variables
    TextView newFactTextView = (TextView) findViewById(R.id.Facts);
    Button mShowFactButton = (Button) findViewById(R.id.newFact);

    View.OnClickListener listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
         // Button comment whatever update with new fact
            String fact = "Ostriches can run faster than horses";
            FactsTextView.setText(fact);
        }
    };
    mShowFactButton.setOnClickListener(listener);
}

1 Answer

jemartin
jemartin
22,295 Points
jemartin
jemartin
22,295 Points

The following line declares a TextView instance, but since you never assign it, the object remains null. private TextView FactsTextView;

In your OnClickListener, you attempt to assign some text to this object. FactsTextView.setText(fact);

It looks like the problem is that you declare two fields (FactsTextView and mShowFact) in your class, but instead of initializing those in your onCreate method, you instead initialize two new local variables (newFactTextView and mShowFactButton).