Android中的课程和活动

Question

Another Java/Android newbie...

My Activity contains a delcaration for a variable of a class that I've defined... public Teams theTeams = null; Within the onCreate method of this Activity, I create an object of that class... Teams theTeams = new Teams(); I've been able to make some changes to this object... theTeams.setName("A", "Jets"); ... which assigns "Jets" to a string in the class. However, from within a private method of the Activity, attempts to refer to "theTeams" give me a null pointer error. I guess there's something about object visibility that I'm not understanding. Can someone clarify?

Answer 1

You declared first public Teams theTeams = null; Then in the onCreate method, you have this

Teams theTeams = new Teams();

So you are initializing a new theTeams object of type Team inside the onCreate , which you can see only in the scope of onCreate .

So when you call a method on theTeams in your private method, the method is called in the object you have declared first outside the onCreate (which is still null)

So inside, your onCreate , you have to use:

theTeams = new Teams();

Something like the following should work (untested):

private Teams theTeams = null;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    theTeams = new Teams();
}

private void myMethod() {
    theTeams.getName();
}