ios - 我很难理解苹果 block 编程的这一部分

Question

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Answer 1

假设你有:

int i = 5; // in stack

然后在 block 中你有:

...
i++; // can't do that, because i now inside the block is a const
...

您要将 __block 添加到 i 声明，以便能够像这样在 block 内更改 i 的值:

__block int i = 5; // remove __block and see the error

void (^myBlock)(void) = ^{
    NSLog(@"[inside block] i = %i", i); // no error even without __block
    i++; // error here without __block
};

myBlock();

NSLog(@"[outside block] i = %i", i);