Question

我在ARC下创建了一个接受块的方法。问题是应用程序不断崩溃，我认为崩溃的原因是ARC正在释放对象。我的问题是，如何解决这个问题，我怎样才能保留对象的引用，以便在块处理之前不会释放对象。

这是.h类

#if NS_BLOCKS_AVAILABLE
typedef void (^KelaMagicalControlCompletionBlock)();
#endif

@interface KelaMagicalControl : NSObject

+(KelaMagicalControl *)controlWithTitle:(NSString *)title message:(NSString *)message;
-(id)initWithTitle:(NSString *)title message:(NSString *)message;

-(void)showWithTouchCompletionBlock:(KelaMagicalControlCompletionBlock)completionBlock;

@end

这是.m类

#import "KelaMagicalControl.h"

@interface KelaMagicalControl()

@property (nonatomic, strong) NSString * title;
@property (nonatomic, strong) NSString * message;

@property (copy) KelaMagicalControlCompletionBlock completionBlock;

@end

@implementation KelaMagicalControl

-(void)dealloc
{
   NSLog(@"deallocated");
}

+ (KelaMagicalControl *)toastWithTitle:(NSString *)title message:(NSString *)message
{
   KelaMagicalControl * magicalControl = [[KelaMagicalControl alloc] initWithTitle:title   message:message];
   return magicalControl;
}
-(id)initWithTitle:(NSString *)title message:(NSString *)message
{
    if(self = [super init])
    {
        _title = title;
        _message = message;
    }
    return self;
}

-(void)showWithTouchCompletionBlock:(void (^)())completionBlock
{

    UIWindow * mainWindow = [[UIApplication sharedApplication]keyWindow];
    UIView * viewTemp = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 300, 100)];
    [viewTemp setTag:10001];
    [viewTemp setBackgroundColor:[UIColor redColor]];
    [mainWindow addSubview:viewTemp];

    UITapGestureRecognizer * tapGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(mainViewTapped)];
    [viewTemp addGestureRecognizer:tapGestureRecognizer];

    self.completionBlock = completionBlock;

}

-(void)mainViewTapped
{
    if(self.completionBlock)
    {
        self.completionBlock();
        self.completionBlock = nil;
    }
}

从控制器类，我将消息发送到自定义类'这样的方法：

-(IBAction)showMagicalControl:(id)sender
{
    NSString * title = @"Title";
    NSString * message = @"This is a very long message";


    KelaMagicalControl * magicalControl = [[KelaMagicalControl alloc] initWithTitle:title message:message];
    [magicalControl showWithTouchCompletionBlock:^{
        NSLog(@"control tapped");
    }];
}

因此它显示控件正常，但是当我点击它时，而不是执行块，它崩溃时出现错误“obj_msgsend”。它甚至没有达到showMagicalControl方法。我认为，当我使用ARC时，它会自动释放，我可以看到dealloc被立即调用（在执行块之前）。如果我创建了magicalRecord的属性并使用它，它不会崩溃，但根据我的要求，我不想使用全局iVar或属性来调用这个块代码。

有什么建议吗？

Answer 1

问题是你的KelaMagicalControl在showMagicalControl：方法结束时被释放，它不会被保留在任何地方。只有您在showWithTouchCompletionBlock：中创建的UIView才会被保留，因为您已将其添加到超级视图，在本例中为窗口。这就是弹出窗口正确显示的原因。但是目标始终是unsafe_unretained，因此当您点击该视图时，gestureRecognizer将尝试调用已经发布的KelaMagicalControl，因此您会崩溃。

您可以通过将KelaMagicalControl作为UIView的子类来轻松解决此问题。我很快就输出了你要做的改变：

.h文件

#import <UIKit/UIKit.h>

#if NS_BLOCKS_AVAILABLE
typedef void (^KelaMagicalControlCompletionBlock)();
#endif

@interface KelaMagicalControl : UIView
{
    NSString* _title;
    NSString* _message;
}

-(id)initWithTitle:(NSString *)title message:(NSString *)message;
-(void)showWithTouchCompletionBlock:(KelaMagicalControlCompletionBlock)completionBlock;

@end

.m文件

#import "KelaMagicalControl.h"

@interface KelaMagicalControl()

@property (nonatomic, strong) NSString * title;
@property (nonatomic, strong) NSString * message;

@property (copy) KelaMagicalControlCompletionBlock completionBlock;

@end

@implementation KelaMagicalControl

-(void)dealloc
{
    NSLog(@"deallocated");
}

+ (KelaMagicalControl *)toastWithTitle:(NSString *)title message:(NSString *)message
{
    KelaMagicalControl * magicalControl = [[KelaMagicalControl alloc] initWithTitle:title   message:message];
    return magicalControl;
}

-(id)initWithTitle:(NSString *)title message:(NSString *)message
{
    self = [super initWithFrame:CGRectMake(10, 10, 300, 300)];
    if (self)
    {
        _title = title;
        _message = message;
    }
    return self;
}

-(void)showWithTouchCompletionBlock:(void (^)())completionBlock
{
    UIWindow * mainWindow = [[UIApplication sharedApplication]keyWindow];
    [self setTag:10001];
    [self setBackgroundColor:[UIColor redColor]];
    [mainWindow addSubview:self];

    UITapGestureRecognizer * tapGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(mainViewTapped)];
    [self addGestureRecognizer:tapGestureRecognizer];

    self.completionBlock = completionBlock;
}

-(void)mainViewTapped
{
    if(self.completionBlock)
    {
        self.completionBlock();
        self.completionBlock = nil;
    }
}
@end

由于您的KelaMagicalControl现在是您正在显示的UIView，因此它将自动保留，因为它具有超级视图。点击视图后，现在可以根据需要执行完成块。确保在完成块的末尾将其从超级视图中删除，否则它将永远不会被释放。

Answer 2

你是对的，magicalControl会被取消分配，因为它结束了他的范围。我没有测试过以下但它应该可以工作。

KelaMagicalControl * magicalControl = [[KelaMagicalControl alloc] initWithTitle:title message:message];
    [magicalControl showWithTouchCompletionBlock:^{
        KelaMagicalControl *retainedVar = magicalControl;
        NSLog(@"control tapped");
    }];

在块内声明一个强引用将保留magicalControl。

Answer 3

一种解决方案是使用UIGestureRecognizer的块API（互联网上有许多版本的这种版本），然后在块中调用[self mainViewTapped]。这会保留您的KelaMagicalControl，并且只要手势识别器可以调用它，就会确保KelaMagicalControl可用。

在ARC中保持局部变量的对象引用

3 个答案: