Objective c 拖动边界

我正在尝试使用以下代码使我的精灵停留在屏幕边框中：

- (BOOL)ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event {
CGPoint touchLocation = [self convertTouchToNodeSpace:touch];
[self selectSpriteForTouch:touchLocation];
return TRUE; }

- (void)ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event {       

CGPoint touchLocation = [self convertTouchToNodeSpace:touch];
if (selSprite) {
CGPoint oldLocation = [touch previousLocationInView:touch.view];
oldLocation = [[CCDirector sharedDirector] convertToGL:oldLocation];
oldLocation = [self convertToNodeSpace:oldLocation];

CGPoint translation = ccpSub(touchLocation, oldLocation);    
CGPoint newPos = ccpAdd(selSprite.position, translation);
selSprite.position = newPos;     }   }

我知道我需要添加一些代码来指定边界。如下所示：

    int width=point.x;
    int height=point.y;
    if (winSize.width-sprite.contentSize.width/2<width) {
        width=winSize.width-sprite.contentSize.width/2;}
    if (winSize.height-sprite.contentSize.height/2<height) {
        height=winSize.height-sprite.contentSize.height/2;}
    if (sprite.contentSize.height/2>height) {
        height=sprite.contentSize.height/2;}                                                    
    if (sprite.contentSize.width/2>width) {
        width=sprite.contentSize.width/2;}

int width=point.x；
整数高度=点y；
if（winSize.width sprite.contentSize.width/2width）{
宽度=sprite.contentSize.width/2；}

但我对目标C还不熟悉，我还不完全了解如何处理它。

明白了！ 只需添加

if（selSprite）{}

这部分代码

    int width=touchLocation.x;
    int height=touchLocation.y;
    if (selSprite.contentSize.width!=width) {
        width=selSprite.contentSize.width/2;}
  if (selSprite.contentSize.height/2<height) {
        height=selSprite.contentSize.height/2;}
    [selSprite setPosition:ccp(width,height)];

int width=touchLocation.x；
int height=touchLocation.y；
if（selSprite.contentSize.width！=宽度）{
宽度=selSprite.contentSize.width/2；}
如果（selSprite.contentSize.height/2）