CODEWITHSUNDEEP
iosobjective-cuigesturerecognizer
Edgar
Edgar

Reputation: 931

Do something While view receives gestures

I want to change a view backgroundColor while it is receiving UILongPressGesture, how can I do it properly? With the code below everything freezes forever, even if I lift my finger it won't unfreeze.

- (void)longPress:(UILongPressGestureRecognizer *)gesture {
 while ([gestureRecognizer state] == UIGestureRecognizerStateChanged) {
        [self.Row2View setBackgroundColor:[UIColor colorWithWhite:0.5 alpha:0.2]];
    }
}

EDIT What I need is: While UILongPressGesture change color , When finger lifts the screen change color back.

Upvotes: 0

Views: 60

Answers (3)

bhr
bhr

Reputation: 2337

Add a property 

@property (copy) UIColor *initialBackgroundColor;

Handle Long Press

- (void)longPress:(UILongPressGestureRecognizer *)gesture
{
    if ([gesture state] == UIGestureRecognizerStateBegan)
    {
        self.initialBackgroundColor = self.Row2View.backgroundColor;
        [self.Row2View setBackgroundColor:[UIColor colorWithWhite:0.5 alpha:0.2]];
    }
    else if ([gesture state] == UIGestureRecognizerStateEnded ||
             [gesture state] == UIGestureRecognizerStateCancelled ||
             [gesture state] == UIGestureRecognizerStateFailed)
    {
        [self.Row2View setBackgroundColor:self.initialBackgroundColor];
    }
}

Upvotes: 0

SolaWing
SolaWing

Reputation: 1722

you use while! when enter the loop, the condition will always be true!

first,change while to if. then according to apple document:

Long-press gestures are continuous. The gesture begins (UIGestureRecognizerStateBegan) when the number of allowable fingers (numberOfTouchesRequired) have been pressed for the specified period (minimumPressDuration) and the touches do not move beyond the allowable range of movement (allowableMovement). The gesture recognizer transitions to the Change state whenever a finger moves, and it ends (UIGestureRecognizerStateEnded) when any of the fingers are lifted.

I think you should use Began State(when gesture got recognized) or Ended State(when a recognized gesture release up). if you don't want to call method continuously when touch moves.

if ([gesture state] == UIGestureRecognizerStateBegan) {
    [self.Row2View setBackgroundColor:[UIColor colorWithWhite:0.5 alpha:0.2]];
}

--- EDIT ---

according to you description, you want to change color when touch and restore when release. so it will be:

if ([gesture state] == UIGestureRecognizerStateBegan) {
    Row2ViewOriginColor = self.Row2View.backgroundColor; // you can declare this var in the class.
    [self.Row2View setBackgroundColor:[UIColor colorWithWhite:0.5 alpha:0.2]];
}
else if ([gesture state] == UIGestureRecognizerStateEnded ||
         [gesture state] == UIGestureRecognizerStateCancelled) {
    [self.Row2View setBackgroundColor: Row2ViewOriginColor];
}

Upvotes: 1

mayqiyue
mayqiyue

Reputation: 1155

Because the "while" block will never break! Just change the "while" block to "if"!

Upvotes: 2

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