Question

I’m an amateur developer creating a short app and I’m having trouble using both the XML file for a particular activity along with Activity’s Java method “setContentView”. I need the method because I am generating numbers from a computation and the number generated is variable depending on different parameters. Therefore, each time I call the computation I have to call:

textView.setText(message + " is " + output);
setContentView(textView);

But I also created several buttons on the Activity’s XML page which I would also like to show up on the Activity’s page. For example, this is one of the buttons I created:

<Button 
    android:layout_marginTop="100dp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_quit"
    android:onClick=".quit" />

However, if I call:

setContentView(R.layout.activity_compute_number);

after the set content view for the variable text message I mentioned earlier, the XML file overrides the text message and the text message never shows up and vice versa if I call the two setContentView methods the other way around. How do I get them both to render on the Activity screen simultaneously?

Answer 1

In your activity_compute_number.xml, you should assign an id to your button and textview. This way you can reference your button and textView.

 <Button
    android:id="@+id/button_compute"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="100dp"
    android:onClick=".quit"
    android:text="@string/button_quit" />

<TextView
    android:id="@+id/textView_answer"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="100dp" />

Notice the android:id=”@+id/button_compute” and android:id=”@+id/textView_answer”. This gives this button and textview id’s called button_compute and textView_answer respectively.

Then change your onCreate to the following:

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

    Button btnCompute = (Button)findViewById(R.id.button_compute);
    TextView tvAnswer = (TextView)findViewById(R.id.textView_answer);


    btnCompute.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            /*
             * DO COMPUTATION here
            */

            tvAnswer.setText(answer);
        }
    });
}

In onCreate() method you set your view to show the layout in your activity_compute_number.xml by calling setContentView() only once. You reference your button and textview by findViewById specifying the id’s you have set in your xml.