CODEWITHSUNDEEP
javaandroideclipse
bryce_macinnis
bryce_macinnis

Reputation: 41

How do you dynamically create buttons in Android?

I am building my first android app and I am trying to fill the screen with buttons that will be eventually populated from an SQLLite database. I can't figure out how to dynamically create a button.Right now my main activity has only a linear layout. When I try to dynamically create a button through the following code:

LinearLayout mainLayout = (LinearLayout)findViewById(R.id.mainLayout);

Button addButton =new Button(this);
addButton.setText("add");

mainLayout.addView(addButton);

My app starts and then unexpectedly quits and LogCat throws these errors:

11-11 15:34:21.622: E/AndroidRuntime(16734): FATAL EXCEPTION: main
11-11 15:34:21.622: E/AndroidRuntime(16734): Process:
com.brycemacinnis.easycook, PID: 16734
11-11 15:34:21.622: E/AndroidRuntime(16734): java.lang.RuntimeException:
Unable to start activity  ComponentInfo{com.brycemacinnis.easycook/com.brycemacinnis.easycook.MainActivity
}:java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.LinearLayout.addView(android.view.View)' on a null object reference

I've tried multiple ways I found online to create the buttons but each time the same thing happens. Is there anyway to fix this error? Eventually I would want the buttons to go into a scrollView.

Upvotes: 0

Views: 46

Answers (1)

Daniel Olsson
Daniel Olsson

Reputation: 688

Your code for creating the buttons is correct

Button addButton = new Button(this);

The problem here is what this tells you:

android.widget.LinearLayout.addView(android.view.View)' on a null object reference

which comes from this line:

mainLayout.addView(addButton);

Why?

Because this line of code returns null:

findViewById(R.id.mainLayout);

Why does it return null?

Probably because you are either doing it too early (for example in onCreate in a Fragment) or you have provided the wrong layout id for your setContentView(R.layout.XXX) call (if you are in an activity).

Upvotes: 2

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