Objective-c – Comparing Touch Coordinates


Is it possible to compare touch coordinates made by the users on the UIView to the one store in a plist or txt format? The argument looks like this;

  if (user touch coordinate == touch coordinate stored in plist or text)
    (do something)
    (do something)

If possible in what format should i write the coordinates in the list and how to associate it inside the program?

thanks in advance and sorry if you find my question a bit noobie.

Best Solution

Not sure if there's a one-liner solution.

On a UITouch instance, the locationInView: method returns a CGPoint struct (x and y coordinates, both of type float). So you can store the x and y coordinates in your plist, then compare them with your current touch's x and y coordinates.

EDIT: Also, when comparing the coordinates, you probably want to use the distance between the two points to determine when you have a "hit".

EDIT: Below is sample code for loading and writing to a property list, where the values are based on a NSDictionary:

- (NSMutableDictionary *)loadDictionaryFromPList: (NSString *)plistName
    NSString *plistPath = [[NSBundle mainBundle] pathForResource:plistName ofType:@"plist"];
    NSDictionary *immutableDictionary = [NSDictionary dictionaryWithContentsOfFile: plistPath];
    NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithDictionary: immutableDictionary];
    return mutableDictionary;

- (void)saveDictionary: (NSDictionary *)mySettings toPList: (NSString *)plistName
    NSString *plistPath = [[NSBundle mainBundle] pathForResource:plistName ofType:@"plist"];
    [mySettings writeToFile: plistPath atomically: YES];

The method to calculate the distance between the two locations of the UITouches:

-(CGFloat) distanceBetween: (CGPoint) point1 and: (CGPoint)point2
    CGFloat dx = point2.x - point1.x;
    CGFloat dy = point2.y - point1.y;
    return sqrt(dx*dx + dy*dy );

And finally, the code that uses the values in the property list to determine if the user hit the previous location:

CGPoint currentTouchLocation = [currentTouch locationInView:self];

// Lookup last Touch location from plist, and handle case when current Touch matches it:
NSMutableDictionary *mySettings = [self loadDictionaryFromPList: @"MySettings"];
NSNumber *lastXCoordinate = [mySettings objectForKey:@"lastXCoordinate"];
NSNumber *lastYCoordinate = [mySettings objectForKey:@"lastYCoordinate"];
if (lastXCoordinate && lastYCoordinate)
    CGPoint lastTouchLocation = CGPointMake([lastXCoordinate floatValue], [lastYCoordinate floatValue]);
    CGFloat distanceBetweenTouches = [self distanceBetween: currentTouchLocation and: lastTouchLocation];
    if (distanceBetweenTouches < 25) // 25 is just an example
        // Handle case where current touch is close enough to "hit" previous one
        NSLog(@"You got a hit!");

// Save current touch location to property list:
[mySettings setValue: [NSNumber numberWithFloat: currentTouchLocation.x] forKey: @"lastXCoordinate"];
[mySettings setValue: [NSNumber numberWithFloat: currentTouchLocation.y] forKey: @"lastYCoordinate"];
[self saveDictionary:mySettings toPList: @"MySettings"];