Android. NullReferenceException of Button

Question

I'm new to Android development, so this is probably easy question. There is Button defined in layout, but when Activity starting I see in debugger this Button is null. How this can happend?

<Button
        android:id="@+id/show_answer_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/show_answer_button"/>

Activity:

        private Button mShowAnswer;
        mShowAnswer = (Button)findViewById(R.id.show_answer_button);
        mShowAnswer.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                if (mAnswerIsTrue) {
                    mAnswerTextView.setText(R.string.true_button);
                }
                else {
                    mAnswerTextView.setText(R.string.false_button);
                }
            }
        });

Have you called `setContentView()` before the above code. Also, make sure you reference the correct layout file. — Shaishav, Aug 31 '16 at 04:26
@Shaishav, no, setContentView() certainly called after this. — andrey.shedko, Aug 31 '16 at 04:30
@VishalThakkar, according his post he can compile and run the app, your idea does not correct. — Saeed Zhiany, Aug 31 '16 at 04:31
@andrey.shedko, you must call `setContentView()` before any view binding in your activity — Saeed Zhiany, Aug 31 '16 at 04:32
@saeedzhiany, yes, you're right, I can start app, but when launched activity with this button, it's throwing NRE. — andrey.shedko, Aug 31 '16 at 04:32
Post the entire activity code with lifecycle methods if possible — Shaishav, Aug 31 '16 at 04:35
Guys, thanks for your help. Yes, that's was about setContentView() in wrong place. @saeedzhiany, please add your comment as answer. — andrey.shedko, Aug 31 '16 at 04:38
Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Anirudh Sharma, Aug 31 '16 at 04:50

score 1 · Answer 1 · answered Aug 31 '16 at 04:42

try this:

 private Button mShowAnswer;

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

     mShowAnswer = (Button)findViewById(R.id.show_answer_button);
            mShowAnswer.setOnClickListener(new View.OnClickListener(){
                @Override
                public void onClick(View v) {
                    if (mAnswerIsTrue) {
                        mAnswerTextView.setText(R.string.true_button);
                    }
                    else {
                        mAnswerTextView.setText(R.string.false_button);
                    }
                }
            });

            }

score 0 · Accepted Answer · edited May 23 '17 at 12:22

0

According to this comment setContentView() method is in wrong place, it's must be place before binding button variable and button xml view.

setContentView(R.layout.your_xml_layout_name);
private Button mShowAnswer;
mShowAnswer = (Button)findViewById(R.id.show_answer_button);

edited May 23 '17 at 12:22

Community

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answered Aug 31 '16 at 04:40

Saeed Zhiany

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Android. NullReferenceException of Button

2 Answers2