CODEWITHSUNDEEP
androidandroid-layout
andrey.shedko
andrey.shedko

Reputation: 3238

Android. NullReferenceException of Button

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);
                }
            }
        });

Upvotes: 0

Views: 102

Answers (2)

Sangram Haladkar
Sangram Haladkar

Reputation: 717

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);
                    }
                }
            });

            }

Upvotes: 1

Saeed Zhiany
Saeed Zhiany

Reputation: 2141

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);

Upvotes: 0

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