UIView is the parent class for display objects on the iPhone (unless you're using Core Animation or OpenGL). Buttons, text fields, and images are all children of UIView.

A view can contain other views. If it does, it is said to be the superview to the contained views, which are called subviews. To add a subview to an existing UIView:

[viewObj addSubview:otherViewObj];

To remove a subview from its superview:

[otherViewObj removeFromSuperview];

To adjust the size or position of a view, see View Frames and Bounds.

Animating Views

A view's size, location, rotation or transparency can be animated using several UIView class methods. You can animate the following view properties:

In iOS 4 and later, you can use animation blocks to animate the above properties. (Older versions of iOS used beginAnimation/commitAnimations.) There are three block-based animation methods you can use:

animateWithDuration:animations:
animateWithDuration:animations:completion:
animateWithDuration:delay:options:animations:completion:

Here's a simple example. This moves a view to a new location:

CGRect newFrame = theView.frame;
newFrame.origin.x += 500;    // shift right by 500pts

[UIView animateWithDuration:1.0 
    animations:^{
        theView.frame = newFrame;
    }];

If you want to run another animation (or trigger some action) after the first animation finishes, use animateWithDuration:animations:completion:

[UIView animateWithDuration:1.0 
    animations:^{
        theView.frame = newFrame;    // move
    }
    completion:^(BOOL finished){
        // code to run when animation completes
        // (in this case, another animation:)
        [UIView animateWithDuration:1.0 
           animations:^{        
              theView.alpha = 0.0;   // fade out
           }
           completion:^(BOOL finished){  
              [theView removeFromSuperview];           
           }];
    }];

To specify animation options (such as the animation curve), or delay the start of animation, use animateWithDuration:delay:options:animations:completion:

[UIView animateWithDuration:1.0 
    delay: 0.5
    options: UIViewAnimationOptionCurveEaseIn
    animations:^{
        theView.frame = newFrame;   // move
    }
    completion:nil];  // no completion handler

Animation options allow you to specify the type of animation, repeat/autoreverse options, and whether to allow user interaction while the view is animating. To specify multiple options:

    options: UIViewAnimationOptionCurveLinear | UIViewAnimationOptionAllowUserInteraction;

Rotation

To rotate a view, apply a CGAffineTransformMakeRotation result to the view's .transform property:

float degrees = 45.0;
float radians = (degrees/180.0) * M_PI; 

[UIView animateWithDuration:0.25
    animations:^{
      theView.transform = CGAffineTransformMakeRotation(radians);
    }];

Undoing Rotations

To restore a view to its original angle, set its transform property to CGAffineTransformIdentity.

theView.transform = CGAffineTransformIdentity;

This example rotates the view by 45 degrees, then rotates it back on completion:

float degrees = 45.0;
float radians = (degrees/180.0) * M_PI; 

[UIView animateWithDuration:0.25
    animations:^{
      theView.transform = CGAffineTransformMakeRotation(radians);
    }
    completion:^(BOOL finished){
    
        [UIView animateWithDuration:0.25
             animations:^{
                theView.transform = CGAffineTransformIdentity;
             }];
    
    }];

See the UIView Class Methods documentation for more info on the various animation methods.

Additional References

• UIView Class Reference
• View Programming Guide: Animations