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
– Shaishav, Commented Aug 31, 2016 at 4:26
@Shaishav, no, setContentView() certainly called after this. — andrey.shedko
– andrey.shedko, Commented Aug 31, 2016 at 4:30
@VishalThakkar, according his post he can compile and run the app, your idea does not correct. — Saeed Zhiany
– Saeed Zhiany, Commented Aug 31, 2016 at 4:31
@andrey.shedko, you must call setContentView() before any view binding in your activity — Saeed Zhiany
– Saeed Zhiany, Commented Aug 31, 2016 at 4:32

Sangram Haladkar · Accepted Answer · 2016-08-31 04:42:01Z

1

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);
                    }
                }
            });

            }

answered Aug 31, 2016 at 4:42

Sangram Haladkar

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Comments

Community · Accepted Answer · 2017-05-23 12:22:50Z

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, 2017 at 12:22

CommunityBot

11 silver badge

answered Aug 31, 2016 at 4:40

Saeed Zhiany

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