How to Remove Null Object Reference Error

Forum|Forum|17 years ago
March 27, 2009
3 replies
1195 views

I am trying to figure out the logic to remove a null reference error that is popping up when an item is not dragged. In the code, I have a stopDrag setup for the stage. It works as expected unless the user clicks the item but doesn't drag it. It causes the variable I have set to bring the name of the dropTarget to be a null which crashes the system. I have tried to declare the variable with a default value but it still doesn't work.

It is the targetStop code that it is crashing on. Is there anyway to default a value so I can do an if / then statement to determine if there is a value? I've tried: if (targetStop == null) but that doesn't seem to work.

Here is the error I am getting: TypeError: Error #1009: Cannot access a property or method of a null object reference.

Any help would be greatly appreciated.

Thanks.

Dave

ActionScript

This topic has been closed for replies.

K

Kurrykid-jzpfVqAuthor

Inspiring

Still not working...the problem is that there is no "dropTarget.name" because I haven't dragged anything and it won't take setting a variable.

here's a question...is there a variable or event that is fired when something is dragged? I could listen for that event and base my code on that. They have startDrag() and stopDrag()...is there anything for the middle of the process like isBeingDragged() or hasBeenDragged().

Thanks.

Dave

A

Andrei1-bKoviI

Inspiring

No, there no such things as isBeenDragged. I think there is a design issue here. What are you trying to accomplish. How you variable targetStop is used? Why do you need it?

K

Kurrykid-jzpfVqAuthor

Inspiring

I need to determine where the movieclip was dropped so that I can go to the frame associated with the selection. I am using the drag like a menu selection so that when you drop on that menu item, you go to that frame. To do that, I need to know what it was dropped on. The targetStop gets the dropTarget.name for me.

There's no doubt in my mind that it is a design issue :-)

I have removed the variable to get the droptarget.name and I am getting the value from the hitTestObject and it appears to be working now...I will test further and see what happens.

Thank you for all the help.

Dave

N

Newsgroup_User

Inspiring

Kurrykid wrote:

> stage.addEventListener(MouseEvent.MOUSE_UP, testStopDrag);
> function testStopDrag(event:MouseEvent):void{
> test_mc.stopDrag();
> var targetStop:String = test_mc.dropTarget.name;
>

Try to set an "if" around it.

if (test_mc != null){
test_mc.stopDrag();
var targetStop:String = test_mc.dropTarget.name;
}

You might set test_mc to null before draging, so it has an initial status.

A

Andrei1-bKoviI

Inspiring

Try to remove the object from stopDrag - it really doesn't matter what stops dragging because only one thing at a time can be dragged anyway and you listener is attached to the stage - no references to non-existing objects:

function testStopDrag(event:MouseEvent):void{
stopDrag();
.....
}

K

Kurrykid-jzpfVqAuthor

Inspiring

Good idea...I have changed it to stopDrag(); However I am still getting the error becuase the variable below it (targetStop) gets the value of the item that was dragged. I need to capture this data if something is dragged.

Any other thoughts?

Thanks.

Dave

A

Andrei1-bKoviI

Inspiring

Because I have no idea how you use this variable, it is hard to say what to do with it. I am not sure why would you make the assignment like this at all. The reason for my doubt is that, again, dragging has a singular target. So, the same object that is dragged is the one that is dropped, correct? So, why not to make this assignment inside the listener that starts dragging - not the one that stops it?

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