Swallowing a ccTouch on ccTouchMoved - iphone

Question

I am attempting to let players drag objects in my game from one part of the screen to another. The problem is, the objects which are to be dragged have layers beneath them that need to receive touches, too. Normally I'd just swallow the touch, but as far as I can tell, that can only be done during ccTouchBegan. I can't tell if the user is attempting to drag an object until after ccTouchMoved is called, so I need a way to explicitly swallow (or otherwise prevent lower layers) from receiving the touch after I've determined that it is a touch I'm interested in (within ccTouchMoved).

Answer 1

I got almost the same problem, but I don't know if my solution would fit here. The main idea was that objects which should be dragged were children on the same CCNode hierarchy with beneath items. The solution consists in the fact that parent disabled children's touch events, then intercepts these events. In case some object was dragged parent sends all event to it, in the other case parent handles the event itself.
Let me try to show what I mean. Create protocol for items which can swallow touches ccTouchMoved:
#protocol SwallowingOnTouchMovedNode
{
-(BOOL) ccTouchMoved:(UITouch*)touch; // not full signature for simpleness (UIEvent should be also here)
}
Then create layer, which will manually handle the touches of its children:
#interface TouchHandler : CCLayer
{
NSMutableArray *draggableChildren_, nonDraggableChildren_, *claimedChildren_;
BOOL isDragging_;
}
#implementation TouchHandler
-(id) init
{
...
self.isTouchEnabled = YES;
draggableChildren_ = [[NSMutableArray alloc] init];
nonDraggableChildren_ = [[NSMutableArray alloc] init];
claimedChildren = [[NSMutableArray alloc] init];
...
}
Create two methods for TouchHandler for adding two types of children - the ones which can be dragged and the others. That methods will disable touches on children so the parent will manually handle them.
-(void) addChild:(CCNode*)child shouldBeDragged:(BOOL)shouldBeDragged
{
NSMutableArray *arrayToAddChild = shouldBeDragged ? draggableChildren_ : nonDraggableChildren_;
[arrayToAddChild addObject:child];
// note, that if the child has its own children, you will need to
// set isTouchEnabled on all of them, as adding all children to array recursively
if ([child respondsToSelector:#selector(setIsTouchEnabled:)]) ((CCLayer*)child).isTouchEnabled = NO;
[self addChild:child]; // maybe you need to call -addChild:zOrder:tag: here
}
Then override touch handles like that:
-(BOOL) ccTouchBegan:(UITouch*)touch
{
for (CCNode *child in draggableChildren)
{
if ([child ccTouchBegin:touch])
{
// this behavior looks like the one in CCTouchDispatcher -
// we claim children which return YES for touchBegin
[claimedChildren addObject:child];
}
}
}
-(void) ccTouchMoved:(UITouch*)touch
{
for (CCNode *child in claimedChildren)
{
if ([(id<SwallowingOnTouchMovedNode>)child ccTouchMoved:touch])
{
isDragging_ = YES;
}
}
// if no one swallowed touches
if (!isDragging_)
{
for (CCNode *child in nonDraggableChildren)
{
// we did not called ccTouchBegan earlier for these items,
// so for consistency we need to call it now
if ([child ccTouchBegin:touch])
{
[child ccTouchMoved:touch];
[claimedChildren addObject:child];
}
}
}
}
-(void) ccTouchEnded:(UITouch*)touch
{
isDragging_ = NO;
for (CCNode *child in claimedChildren)
{
[child ccTouchEnded];
}
}
Do not forget to implement -ccTouchCancelled. This code is pretty concrete, so you may need to make some changes, but I hope I have explained my idea. In general, the TouchHandler may not even be the CCLayer to work like this, just add it as targeted delegate for receiving touches.
There is another way, which seems to be more consistent and correct from OOP point of view, but I am not sure about it. The behavior in ccTouchBegin, ccTouchMoved and ccTouchEnded almost duplicates the one in the CCTouchDispatcher. You can subclass it and override some methods for receiving touch events and implement -(BOOL)ccTouchMoved, as I've done. Also, I don't know if we can replace default CCTouchDispatcher. Hope this will help!