Iphone:无法从 UITabBarController 加载模态视图

Question

我希望能够使用 UIViewController 的实例呈现模态视图。当从标准 UIViewController ( Root View )呈现它时，我这样做没有问题。我已经设置了一个委托(delegate)来使呈现的 Root View 关闭模态视图。这是根据 Apple 最佳实践的。

当我尝试在从 UITabBarController 加载 Root View 时使相同的 Root View 呈现模态视图时，我遇到了严重的问题。前三次我加载 View 没有问题，但第四次调试器显示在尝试调用委托(delegate)方法时 Root View 已被释放(“消息发送到已释放的实例”)。我的猜测是，在显示模态视图时， Root View 已自动释放。我怎样才能避免这种情况？

我设置的示例使用 UITabBarController 的模板，从第一个 View 呈现模态视图:

FirstViewController.h( Root View Controller ):

#import <UIKit/UIKit.h>

@protocol ModalDelegate;
@interface FirstViewController : UIViewController <ModalDelegate>{
}

-(IBAction)startPressed:(id)sender;
@end

FirstViewController.m:

#import "FirstViewController.h"
#import "ModalViewController.h"


@implementation FirstViewController

-(IBAction)startPressed:(id)sender
{
 ModalViewController *modal=[[ModalViewController alloc] init];
 modal.delegate=self;
 [self presentModalViewController:modal animated:TRUE];
 [modal release];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (void)dealloc {
    [super dealloc];
}

#pragma mark Modal Delegate
-(void)modal:(ModalViewController *)controller
{
 [self dismissModalViewControllerAnimated:YES];
}

@end

ModalViewController.h:

#import <UIKit/UIKit.h>

@protocol ModalDelegate;


@interface ModalViewController : UIViewController {
 id<ModalDelegate> delegate;

}

@property (assign) id<ModalDelegate> delegate;

- (IBAction)OKPressed:(id)sender;

@end

@protocol ModalDelegate <NSObject>

@optional
-(void)modal:(ModalViewController *)controller;

@end

ModalViewController.m:

#import "ModalViewController.h"

@implementation ModalViewController
@synthesize delegate;
- (IBAction)OKPressed:(id)sender
{
 if ([self.delegate respondsToSelector:@selector(modal:)]) //Check to see if method responds to selector
 {
  [self.delegate modal:self];
 }
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (void)dealloc {
 [delegate release];
    [super dealloc];
}

@end

Answer 1

您不应该在 ModalViewController 的 dealloc 实现中释放委托(delegate)，因为您(正确地)没有保留它。

此外，您可以关闭模​​态 View Controller 本身，而不是设置委托(delegate)。我觉得这个更简单。这是 iPhone 开发中心对 dismissModalViewControllerAnimated: 的讨论

The parent view controller is responsible for dismissing the modal view controller it presented using the presentModalViewController:animated: method. If you call this method on the modal view controller itself, however, the modal view controller automatically forwards the message to its parent view controller.