Graphics Programs Reference
In-Depth Information
To zoom, you must implement the method
viewForZoomingInScrollView:
in the
UIScrollView
's
delegate
. This method returns the instance of the view to zoom in
on. The view will be the instance of
HypnosisView
, and the
UIScrollView
's
del-
egate
will be the
HypnosisterAppDelegate
.
Currently,
HypnosisterAppDelegate
has a pointer to
HypnosisView
in a local
variable in
application:didFinishLaunchingWithOptions:
. However, to
zoom,
HypnosisterAppDelegate
will need access to that view in another method -
viewForZoomingInScrollView:
. This means
HypnosisterAppDelegate
needs an instance variable that points to a
HypnosisView
instead of a local variable. In
HypnosisterAppDelegate.h
, declare that
HypnosisterAppDelegate
con-
forms to
UIScrollViewDelegate
and declare an instance variable to hold the
Hyp-
nosisView
.
#import <UIKit/UIKit.h>
// Don't forget this import statement!
#import "HypnosisView.h"
@interface HypnosisterAppDelegate : UIResponder
<UIApplicationDelegate
, UIScrollViewDelegate
>
{
HypnosisView *view;
}
@property (strong, nonatomic) UIWindow *window;
@end
Now, in
HypnosisterAppDelegate.m
, put the
HypnosisView
into the instance
variable instead of a local variable.
HypnosisView *view = [[HypnosisView alloc] initWithFrame:screenRect];
view = [[HypnosisView alloc] initWithFrame:screenRect];
[scrollView addSubview:view];
Finally, implement
viewForZoomingInScrollView:
in
HypnosisterAp-
pDelegate.m
to return this view.
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
return view;
}
Build and run the application. Pinch and pull with two fingers to zoom in and out. (On the
simulator, you can simulate two fingers by holding down the Option key, clicking, and
then moving the mouse.) Pan with one finger to scroll once you have zoomed in.
