在ARC中保留局部變量的對象引用

Question

我已經在ARC下創建了一個類，其中有一些方法接受塊。問題是應用程序不斷崩潰，我認爲崩潰的原因是對象正在由ARC發佈。我的問題是，我該如何解決這個問題，我如何保持對象的引用，以便在對塊進行處理之前不會釋放對象。

這裏是.H類

#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 

這裏的m級

#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; 
    } 
} 

從控制器類，我將消息發送到定製類的方法是這樣的：

-(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"); 
    }]; 
} 

所以它笑控制很好，但是當我點擊它時，而不是執行塊，它會崩潰，出現錯誤「obj_msgsend」。它甚至沒有達到showMagicalControl方法。我想，當我使用ARC時，它會自動發佈，我可以看到dealloc立即被調用（在執行block之前）。它不會崩潰，如果我創建一個magicalRecord的屬性並使用它，但根據我的要求，我不想使用全局iVar或屬性只是調用此代碼塊。

有什麼建議嗎？

Answer 1

問題是你的KelaMagicalControl在showMagicalControl：方法的末尾被釋放，它不會被保留在任何地方。只有你在showWithTouchCompletionBlock中創建的UIView：會被保留，因爲你將它添加到了超級視圖，在這個例子中是窗口。這就是爲什麼彈出窗口顯示正確。但是一個目標總是不安全的，所以當你點擊那個視圖時，gestureRecognizer會嘗試調用你已經發布的KelaMagicalControl，這樣你就會崩潰。

您可以通過將您的KelaMagicalControl作爲UIView的子類輕鬆解決此問題。我趕緊打出來的變化，你不得不做：

.h文件中

#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文件現在

#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 

由於您KelaMagicalControl是UIView的你重新顯示，它會自動保留，因爲它有一個超級視圖。當您點擊視圖時，完成模塊現在可以隨意執行。確保在完成塊結束時將其從超級視圖中移除，否則它將永遠不會被釋放。

Answer 2

你是對的，magicalControl被釋放，因爲它結束了他的範圍。我沒有測試以下內容，但它應該可以工作。

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

在block中聲明一個強引用會保留magicalControl。

Answer 3

一種解決方案是使用UIGestureRecognizer的塊API（有許多版本在Internet上浮動），然後在該塊中調用[self mainViewTapped]。這會保留您的KelaMagicalControl，並確保KelaMagicalControl只要手勢識別器可以調用它即可使用。