CODEWITHSUNDEEP
androidclass
Tom humphries
Tom humphries

Reputation: 49

FindViewById Null When Used In Child Class

I'm using a child class which extends from main to setup some buttons. I am able to change variables created in main, such as TotalMoney from within child.

The problem is findViewById is giving a nullpointer exception. The code within buildthem() works fine when used in the main class.

I am using setContentView(R.layout.main); from within OnCreate in main. The Child class is instantiated and called from OnResume in main class.

Do I need to setContentView in the child aswell, or pass the content view from the main class somehow?

package com.chewyapps.markettrader;

         class child extends main {

     void buildthem(){

         TotalMoney = TotalMoney + 9999;


          Button MenuButton = (Button) findViewById(R.id.Menu);
           //etc

     }
}

I can't findViewById in Oncreate because the full code will use

         for(i=0; i<buttonIDs.length; i++) {                
                    Button b = (Button) findViewById(buttonIDs[i]);
//do other stuff    
    }

The for loop is needed for other things relating to each button. If I can get the basic example working though I assume the full code will work.

It hadn't occured to me before to mention this, but the child class is in a seperate file called child.java, from my main.java file in onResume I use:

child childObject = new child ();
     childObject.buildthem();

Upvotes: 1

Views: 907

Answers (2)

dave.c
dave.c

Reputation: 10908

Why not put this line:

Button MenuButton = (Button) findViewById(R.id.Menu);

in onCreate(), then you can either pass MenuButton into buildthem() as a parameter or reference it directly, depending on your design.

Please note that Java convention is to have variable names start with a lowercase letter, so menuButton not MenuButton.

EDIT
Then why not create an array of Buttons in onCreate() that you can later iterate through?

Button myButtons[] = new Button[buttonIDs.length];
for(int i=0; i<buttonIDs.length; i++) {                
    myButtons[i] = (Button) findViewById(buttonIDs[i]);
}

Then just iterate over the myButtons array in your child class.

Upvotes: 1

Anthony Graglia
Anthony Graglia

Reputation: 5435

What about:

Button MenuButton = (Button) this.findViewById(R.id.Menu);

or

Button MenuButton = (Button) Child.this.findViewById(R.id.Menu);

Upvotes: 0

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