using onClickView to call another class

Question

I want to use a button click to pass selection parameters to another class that will build a map screen using the passed parameters. I am focused on getting my button action working. I a using onCLickListener and onCLickView as follows

Class1:

public class Class1  extends Activity implements OnClickListener {

    Class2 class2;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

..........

       Button button = (Button)findViewById(R.id.btn_configup1);
        button.setOnClickListener(this);        
   }

    public void onClick(View v) {
        Class2 class2 = new Class2();
        //Save state.. selections and params and use bundle
        //to pass into class2
        class2.execMapBuild();

    }    


}


Class2:

public class Class2 extends MapActivity {

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.drawable.navup);
}


public void execMapBuild() {    
        finish(); //just in case we return.
        Intent intent = new Intent(CLass2.this, Class2.class);
        startActivity(intent);

    }

I have everything working except the desired button action. I want the button click in Class1.onVlickView to call Class2.execMapBuild using the button click action. I have the button click capturing the action and calling the execMapBuild method on Class2. But I get a NullPointerException as it moves from startActivity(intent) into onCreate.

I have tried several other ways of nailing this down, but this seems the best and I seem close to figuring it out. I would really appreciate an explanation of what I may be missing. Added code that was initially not copied in.

Answer 1

To expand on @Heiko Rupp's answer, if you want Class2 to display a map, it needs to extend something like Activity. As such, you can't just call it with a normal method. You need to register the Activity in your manifest and then call it using an Intent. Here is a sample of the kind of thing you should be doing:

public class Class1 extends Activity implements OnClickListener {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
        Button button = (Button)findViewById(R.id.btn_configup1);
        button.setOnClickListener(this);        
   }

    public void onClick(View v) {
        Intent intent = new Intent(Class1.this,Class2.class);
        intent.putExtra("key","data");
        ...
        startActivity(intent);
    }
}

public class Class2  extends MapActivity {

    String mData;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
        Bundle extras = getIntent().getExtras();
        if (extras != null) {
            mData = extras.getString("key");
            ...
        }
        ...
    }
}

Can I also suggest that you use more descriptive class names than Class1 and Class2.

Answer 2

Class2 is no activity, so the callbacks of an Activity will not be called by the system.

And if it were an Activity, you could not just call into it via new Class2(), as still the callbacks are not executed.

Try to clean this up and then start Class2 activity from Class1 with an Intent as you are doing within execMapBuild().