我正在尝试从定义为类的一部分的 obj-c 块访问类 ivars。这里有什么不明白的？

发布于 2024-10-29 19:36:51 字数 689 浏览 0 评论 0原文

//class definition
@interface class1 : NSObject {
    NSMutableArray *array ;
    void (^test)() ;
}
@property( nonatomic,assign ) NSMutableArray *array  ;
@property( nonatomic,readonly ) void (^test)()  ;
@end

// implementation

@implementation class1

@synthesize array ;
@synthesize test ;

- (id)init
{
    self = [super init];
    a = [NSMutableArray arrayWithObjects:@"1",@"2", nil] ;
    test = ^ () {
        NSLog(@"length of array = %d",(int)[array count]);
    } ;
    return self;
}

// from main

    class1 *c = [[class1 alloc] init] ;

    c.test();

只要函数“c.test()”访问简单的ivars，即char、int等，c.test()就会干净地执行并返回。我尝试访问 obj-c 对象，但出现异常。我缺少什么？

原文

//class definition
@interface class1 : NSObject {
    NSMutableArray *array ;
    void (^test)() ;
}
@property( nonatomic,assign ) NSMutableArray *array  ;
@property( nonatomic,readonly ) void (^test)()  ;
@end

// implementation

@implementation class1

@synthesize array ;
@synthesize test ;

- (id)init
{
    self = [super init];
    a = [NSMutableArray arrayWithObjects:@"1",@"2", nil] ;
    test = ^ () {
        NSLog(@"length of array = %d",(int)[array count]);
    } ;
    return self;
}

// from main

    class1 *c = [[class1 alloc] init] ;

    c.test();

as long as the function "c.test()" accesses simple ivars, i.e. char, int, etc. c.test() executes and returns cleanly. i try to access an obj-c object, i get exceptions.
what am i missing?

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等风来 2024-11-05 19:36:51

BJ是正确的，您需要遵循内存管理的规则，但是在这种情况下，答案与块有关。

当您的代码当前所示，array的普通属性将起作用，直到当前的Autorelease池排水管为止。如果您为这些“ class1”对象中的一个Alloc/Init，并立即尝试使用array属性，它将起作用（因为在对象的初始化和时间的时间之间不会排干autorelease池您尝试访问数组）。

但是，一旦将块放在那里，情况就不再如此。当您使用^{...}语法声明块时，该块将在呼叫堆栈的当前帧中分配。当您从INIT方法返回时，当前帧将弹出。 Ivar块仍然保留一个内存地址，但是该地址不再存在一个块。当堆栈框架被拆除时，它被破坏了。

避免这种情况的方法是将堆栈从堆栈中复制到堆上，然后使用块：

test = [^{  NSLog(@"block!"); } copy];

BJ's correct that you need to follow the rules of memory management, but in this case, the answer does have to do with blocks.

As your code currently stands, the normal property of array will work until the current autorelease pool drains. If you alloc/init one of these "class1" objects and immediately attempt to use the array property, it will work (because no autorelease pool will have been drained between the initialization of the object and the time at which you attempt to access the array).

However, once you put the block in there, this is no longer the case. When you declare a block using the ^{ ... } syntax, this block is allocated in the current frame on the call stack. When you return from the init method, the current frame is popped. The block ivar still holds a memory address, but a block no longer exists at that address. It was destroyed when the stack frame was removed.

The way to avoid this is to copy the block off of the stack and onto the heap, and then use that block instead: