Identifying pinch gesture drag gesture on iPhone? - iphone

Question

I have a small image on a view. The view is the object process multi-touch actions. If a finger drag on the view, the image will translate its position. And if user use 2 fingers to make pinch gesture, the image will scale its size. And I do work as section code below:
//touch detect methods
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
NSLog(#"Touch began");
//Devide into 2 cases: 1 touch and 2 touches.
if ([touches count] == 1) {
NSLog(#"Touch began cout = 1");
currentImageCenter = focusImage.center;
UITouch *touch = [[touches allObjects] objectAtIndex:0];
previousPoint = [touch locationInView:self];
isTwoFingerTouching = FALSE;
}
else if([touches count] == 2){
NSLog(#"Touch began cout = 2");
UITouch *touch = [[touches allObjects] objectAtIndex:0];
beginFirstPoint = [touch locationInView:self];
touch = [[touches allObjects] objectAtIndex:1];
beginSecondPoint = [touch locationInView:self];
isTwoFingerTouching = TRUE;
}
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
if ([touches count] == 1 && isTwoFingerTouching == FALSE) {
UITouch *touch = [touches anyObject];
CGPoint currentPosition = [touch locationInView:self];
//Calculate distance
double deltaX = currentPosition.x - previousPoint.x;
double deltaY = currentPosition.y - previousPoint.y;
NSLog(#"Touch move detect 1 touch ");
focusImage.center = CGPointMake(currentImageCenter.x+deltaX, currentImageCenter.y+deltaY);
}
else if([touches count] == 2){
NSLog(#"Touch move detect 2 touches");
CGPoint currentFirstPoint;
CGPoint currentSecondPoint;
UITouch *touch = [[touches allObjects] objectAtIndex:0];
currentFirstPoint = [touch locationInView:self];
CGPoint previousFirstPoint = [touch previousLocationInView:self];
touch = [[touches allObjects] objectAtIndex:1];
currentSecondPoint = [touch locationInView:self];
CGPoint previousSecondPoint = [touch previousLocationInView:self];
//Compare previous points with current points.
//Pinch gesture
CGFloat beginDistance = distanceBetweenPoints(previousFirstPoint, previousSecondPoint);
CGFloat currentDistance = distanceBetweenPoints(currentFirstPoint, currentSecondPoint);
if (currentDistance > 0 && beginDistance > 0) {
double scale = currentDistance/beginDistance;
NSLog(#"%f", scale);
//Rotation
CGPoint vector1 = CGPointMake(previousFirstPoint.x - previousSecondPoint.x, previousFirstPoint.y - previousSecondPoint.y);
CGPoint vector2 = CGPointMake(currentFirstPoint.x - currentSecondPoint.x, currentFirstPoint.y - currentSecondPoint.y);
//[vector1, vector2].
double zValue = vector1.x*vector2.y - vector1.y*vector2.x;
CGFloat rotateAngle = angleBetweenLines(previousFirstPoint, previousSecondPoint, currentFirstPoint, currentSecondPoint);
//zValue < 0, vector1 rotate counter-clockwise, so the angle should be negative.
if (zValue < 0) {
rotateAngle = -rotateAngle;
}
//Don't allow to zoom out if the image is too small
if (scale > 1 || focusImage.frame.size.width > 30) {
CGAffineTransform previousTransform = focusImage.transform;
CGAffineTransform mixTransform = CGAffineTransformConcat(CGAffineTransformMakeScale(scale, scale), CGAffineTransformMakeRotation(rotateAngle));
focusImage.transform = CGAffineTransformConcat(previousTransform, mixTransform);
}
}
}
}
But the problem is: I can't identify whether 1 finger or 2 fingers on screen. When I touch 2 fingers, and I move (for rotate and scale) those fingers, [touches count] in touchesMoved: method still equal 1 occasionally. Any one experienced this, please tell me how to solve my problem?

Answer 1

Any reason why you are not using UIGestureRecognizers? It will save you a lot of work if you just use a UIPanGestureRecognizer and a UIPinchGestureRecognizer.
In any case, iOS has always behaved like that. Unless you touch with both fingers at the exact same millisecond, you will detect a one finger touch first then detect two finger touch. You need to employ some sort of a cancelling mechanism in your code if you still want to go the -touchesBegan..., -touchesMoved..., etc., method.