帶塊參數的NSInvocation

Question

我正在嘗試將塊參數傳遞給NSInvocation ，但應用程序崩潰了。 調用發出網絡請求並調用成功或失敗塊。 我認為問題是在網絡請求完成之前會釋放塊。 我設法讓它與一些Block_copy hackery一起工作，並且它不使用Instruments報告任何泄漏。

問題： - 即使靜態分析儀或儀器沒有報告，泄漏是否可能存在？ - 有沒有更好的方法來“保留”這個區塊？

// Create the NSInvocation
NSMethodSignature *methodSignature = [target methodSignatureForSelector:selector];
NSInvocation* invoc = [NSInvocation invocationWithMethodSignature:methodSignature];
[invoc setTarget:target];
[invoc setSelector:selector];

// Create success and error blocks.
void (^successBlock)(id successResponse) = ^(id successResponse) {
    // Some success code here ...
};

void (^errorBlock)(NSError *error) = ^(NSError *error) {
    // Some failure code here ...
};

/*
Without the two Block_copy lines, the block gets dealloced too soon
and the app crashes with EXC_BAD_ACCESS
I tried [successBlock copy] and [failureBlock copy] instead,
but the app still crashes.
It seems like Block_copy is the only way to move the block to the heap in this case.
*/
Block_copy((__bridge void *)successBlock);
Block_copy((__bridge void *)errorBlock);
// Set the success and failure blocks.
[invoc setArgument:&successBlock atIndex:2];
[invoc setArgument:&errorBlock atIndex:3];

[invoc retainArguments]; // does not retain blocks

// Invoke the method.
[invoc invoke];

更新：我將代碼更新到下面。 塊是NSMallocBlocks ，但應用程序仍然崩潰。

// Create success and error blocks.
int i = 0;
void (^successBlock)(id successResponse) = ^(id successResponse) {
    NSLog(@"i = %i", i);
    // Some success code here ...
};

void (^errorBlock)(NSError *error) = ^(NSError *error) {
    NSLog(@"i = %i", i);
    // Some failure code here ...
};

/*** Both blocks are NSMallocBlocks here ***/
// Set the success and failure blocks.
void (^successBlockCopy)(id successResponse) = [successBlock copy];
void (^errorBlockCopy)(NSError *error) = [errorBlock copy];

/*** Both blocks are still NSMallocBlocks here - I think copy is a NoOp ***/

// Set the success and failure blocks.
[invoc setArgument:&successBlockCopy atIndex:2];
[invoc setArgument:&errorBlockCopy atIndex:3];

[invoc retainArguments]; // does not retain blocks

// Invoke the method.
[invoc invoke];

這些塊在鏈中傳遞如下：

NSInvocation → NSProxy （使用forwardInvocation: NSInvocation forwardInvocation: ）→ method1 → methodN

methodN最終根據HTTP響應調用成功或失敗塊。

我是否需要在每個階段復制塊？ 上面的例子討論了第一個NSInvocation 。 我還需要[invocation retainArguments]; 在每個適當的步驟？ 我正在使用ARC。

Answer 1

Block_copy ，實際上[block copy] 返回副本。 他們不會在同一位置用副本神奇地切換原件。 所以至少我認為你想要：

successBlock = Block_copy((__bridge void *)successBlock);
errorBlock = Block_copy((__bridge void *)errorBlock); 

（或者，相當於， successBlock = [successBlock copy]; ... ）

否則，您正在創建副本，不對它們執行任何操作，仍然將原始文件傳遞給調用。

編輯：所以，我把以下代碼放入一個項目：

@interface DummyClass: NSObject
@end

typedef void (^ successBlock)(id successResponse);
typedef void (^ failureBlock)(NSError *error);

@implementation DummyClass

- (id)init
{
    self = [super init];

    if(self)
    {
        SEL selector = @selector(someMethodWithSuccess:failure:);
        id target = self;

        // Create the NSInvocation
        NSMethodSignature *methodSignature = [target methodSignatureForSelector:selector];
        NSInvocation* invoc = [NSInvocation invocationWithMethodSignature:methodSignature];
        [invoc setTarget:target];
        [invoc setSelector:selector];

        // Create success and error blocks.
        void (^successBlock)(id successResponse) = ^(id successResponse) {
            // Some success code here ...
            NSLog(@"Off, off, off with %@", successResponse);
        };

        void (^errorBlock)(NSError *error) = ^(NSError *error) {
            // Some failure code here ...
            NSLog(@"Dance, dance, dance till %@", error);
        };

        successBlock = [successBlock copy];
        errorBlock = [errorBlock copy];

        // Set the success and failure blocks.
        [invoc setArgument:&successBlock atIndex:2];
        [invoc setArgument:&errorBlock atIndex:3];

        [invoc retainArguments]; // does not retain blocks

        // Invoke the method.
        double delayInSeconds = 2.0;
        dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
        dispatch_after(popTime, dispatch_get_main_queue(),
        ^{
            [invoc invoke];

        });
    }

    return self;
}

- (void)someMethodWithSuccess:(successBlock)successBlock failure:(failureBlock)failureBlock
{
    NSLog(@"Words:");
    successBlock(@[@"your", @"head"]);
    failureBlock([NSError errorWithDomain:@"you're dead" code:0 userInfo:nil]);
}

@end

並在application:didFinishLaunchingWithOptions:結束時添加以下內容application:didFinishLaunchingWithOptions: ::

DummyClass *unusedInstance = [[DummyClass alloc] init];

結果是在啟動程序兩秒后，控制台上出現以下內容：

2013-06-02 20:11:56.057 TestProject[3330:c07] Words:
2013-06-02 20:11:56.059 TestProject[3330:c07] Off, off, off with (
    your,
    head
)
2013-06-02 20:11:56.060 TestProject[3330:c07] Dance, dance, dance till Error Domain=you're dead Code=0 "The operation couldn’t be completed. (you're dead error 0.)"