Question

This should be easy.

I’ve got a method to move a view up and down and while doing so I move a UIButton over and down… then move the button back to its original position when the method runs again.

I thought I could get the original position of the button with float originalCenterX = topSubmitButton.center.x and float originalCenterY = topSubmitButton.center.y but of course those are overwritten with the center of the button when the method is hit for the second time.

How does one preserve a variable over multiple iterations of a method?

-(IBAction)scrollForComment { 

[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:0.5]; 

CGRect rect = self.view.frame;

NSLog(@"button center x = %f y = %f",topSubmitButton.center.x,topSubmitButton.center.y);
float originalCenterX = topSubmitButton.center.x;
float originalCenterY = topSubmitButton.center.y;

if (commentViewUp) {
    rect.origin.y = self.view.frame.origin.y + 80;// move down view by 80 pixels
    commentViewUp = NO;

    CGPoint newCenter = CGPointMake( 57.0f , 73.0f); // better to calculate this if you are going to rotate to landscape

    [UIView beginAnimations:nil context:nil]; 
    [UIView setAnimationDuration:0.5f];
    topSubmitButton.center = newCenter;
    [UIView commitAnimations];

} else { // toggling the view's location
    rect.origin.y = self.view.frame.origin.y - 80;// move view back up 80 pixels
    commentViewUp = YES;


    CGPoint newCenter = CGPointMake(160 , 74.0f + topSubmitButton.center.y);// would like to calculate center
    [UIView beginAnimations:nil context:nil]; 
    [UIView setAnimationDuration:0.5f];
    topSubmitButton.center = newCenter;
    [UIView commitAnimations];
  }

self.view.frame = rect;

[UIView commitAnimations];

}

Bonus if you can tell me how to put the center of a view in a CGPoint’s x value.

Answer 1

You can use a static variable to preserve its contents between method calls. However, the initializer must be constant, so you cannot call a method to initialize it. What you can do is make the initial value invalid, and test for this before setting the variable.

-(IBAction)scrollForComment {
    static float originalCenterX = −1, originalCenterY = −1; // Assuming −1 would be an invalid value
    if(originalCenterX == −1 && originalCenterY == −1) {
        CGPoint temp = topSubmitButton.center;
        originalCenterX = temp.x;
        originalCenterY = temp.y;
    }
    ...

Bonus if you can tell me how to put the center of a view in a CGPoint’s x value.

I am not sure what you meant by this. If you want to be able to set only the x coordinate of the center, you will need to get the current center, change the x coordinate, and save the new point.

CGPoint temp = topSubmitButton.center;
temp.x = newXValue;
topSubmitButton.center = temp;