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iphone drag and drop weird jumpy movement
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    NSString *touchClass = [NSString stringWithFormat:@"%@",[[touch view] class]];

    if ([touchClass isEqualToString:[NSString stringWithFormat:@"%@",[AnagramLetter class]]]) {
        NSLog(@"start moving");
    }
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    NSString *touchClass = [NSString stringWithFormat:@"%@",[[touch view] class]];
    CGPoint location = [touch locationInView:touch.view];
    if ([touchClass isEqualToString:[NSString stringWithFormat:@"%@",[AnagramLetter class]]]) {
        NSLog(@"touch view centre (x,y) - (%f,%f)",touch.view.center.x,touch.view.center.y);
        NSLog(@"location (x,y) - (%f,%f)",location.x,location.y);
        touch.view.center = location;
    }
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    NSString *touchClass = [NSString stringWithFormat:@"%@",[[touch view] class]];

    if ([touchClass isEqualToString:[NSString stringWithFormat:@"%@",[AnagramLetter class]]]){
        NSLog(@"Now stop moving!");
    }
}

[touch locationInView:[touch.view superview]];

if ([touchClass isEqualToString:[NSString stringWithFormat:@"%@",[AnagramLetter class]]]) {
        UITouch * touch = [touches anyObject];
        CGPoint previous = [touch previousLocationInView:[touch.view superview]];
        CGPoint current = [touch locationInView:[touch.view superview]];
        CGPoint displacement = CGPointMake(current.x - previous.x, current.y - previous.y);

        CGPoint center = touch.view.center;
        center.x += displacement.x;
        center.y += displacement.y;
        touch.view.center = center;
}