Java Development

[maxjmay]

HI, when I select my options and click on the button, I want it to close the current screen, and open up a different screen, but I get the error NullPointerException.

// Add Selected Field Change
	    HorizontalFieldManager hfm5 =  new HorizontalFieldManager(Field.FIELD_HCENTER | Field.FIELD_VCENTER);
	    final String choices[] = {"General","On The Course","On The Tee","On The Green","In The Bunker"};
	    final ObjectChoiceField objsel = new ObjectChoiceField("Select a Chapter",choices,0);
	    hfm5.add(objsel);
	    add(hfm5);
	   	    	    
	    
	 // Add Button To Page   
	    HorizontalFieldManager hfm4 =  new HorizontalFieldManager(Field.FIELD_HCENTER | Field.FIELD_VCENTER);
	    ButtonField mySubmitButton = new ButtonField("Tee Off",ButtonField.CONSUME_CLICK);
        hfm4.add(mySubmitButton);
        add(hfm4);
        
        mySubmitButton.setChangeListener(new FieldChangeListener(){
        	public void fieldChanged(Field Field, int context){  
        		final String selectedValue = choices[objsel.getSelectedIndex()];
        		if(selectedValue.equals("General"))
                {
        		General general = new General(); 	 
       	        UiApplication.getUiApplication().popScreen(Ui.getUiEngine().getActiveScreen());
                UiApplication.getUiApplication().pushScreen(general);
                }
        		
        		else if(selectedValue.equals("On The Course"))
                {
        		OnCourse oncourse = new OnCourse(); 	 
       	        UiApplication.getUiApplication().popScreen(Ui.getUiEngine().getActiveScreen());
                UiApplication.getUiApplication().pushScreen(oncourse);
                }
        		
        		else if(selectedValue.equals("On The Tee"))
                {
        		OnTee ontee = new OnTee(); 	 
       	        UiApplication.getUiApplication().popScreen(Ui.getUiEngine().getActiveScreen());
                UiApplication.getUiApplication().pushScreen(ontee);
                }
        		
        		else if(selectedValue.equals("On The Green"))
                {
        		OnGreen ongreen = new OnGreen(); 	 
       	        UiApplication.getUiApplication().popScreen(Ui.getUiEngine().getActiveScreen());
                UiApplication.getUiApplication().pushScreen(ongreen);
                }
        		
        		else if(selectedValue.equals("In The Bunker"))
                {
        		InBunker inbunker = new InBunker(); 	 
       	        UiApplication.getUiApplication().popScreen(Ui.getUiEngine().getActiveScreen());
                UiApplication.getUiApplication().pushScreen(inbunker);
                }
        		
        		}});

[simon_hain]

use the debugger and find out where the nullpointer is thrown.

you can also just use close() to close the current screen.

[deLik]

Try to:
1) pushScreen(newScreen);
2) popScreen(oldScreen);

[maxjmay]

I tried pushing the new screen, and then popping the old screen but I still get the same error. I tried debugging and it higlighted the
General general = new General();
part of my code.

[simon_hain]

you can step into code, most likely the constructor has a nullpointer somewhere.

[deLik]

1) check your General() class for NullPointers
2) publish your stacktrace here

3)  publish your General() class here too 

[maxjmay · Accepted solution]

Hi everyone, managed to solve my problem, on my General screen, I was drawing a picture on the screen, but hadn't chosen one yet, so left the file name blank. When I deleted this it worked.
Cheers,
Max.