NSValue:getValue:奇怪的行为，为什么会这样?

问题描述

我尝试将CGRect传递给NSInvocation(setArgument:atIndex :).我用NSValue包装它，推到NSArry，然后从NSArray获取并使用NSValue(getValue :).调用(getValue :)方法会导致声明的索引NSInteger i的更改.谁能说为什么会这样?

I try to pass CGRect to NSInvocation (setArgument:atIndex:). I wrap it by NSValue, push to the NSArry,then get from NSArray and use NSValue (getValue:). Calling of (getValue:) method causes the changing of before declared index NSInteger i. Can anybody say why does this happen?

 NSString className = @"UIButton";
    Class cls = NSClassFromString(className);
    cls pushButton5 = [[cls alloc] init];
    CGRect rect =CGRectMake(20,220,280,30);
    NSMethodSignature *msignature1;
    NSInvocation *anInvocation1;

    msignature1 = [pushButton5 methodSignatureForSelector:@selector(setFrame:)];
    anInvocation1 = [NSInvocation invocationWithMethodSignature:msignature1];

[anInvocation1 setTarget:pushButton5];
[anInvocation1 setSelector:@selector(setFrame:)];
NSValue* rectValue = [NSValue valueWithCGRect:rect];
NSArray *params1;
params1= [NSArray arrayWithObjects:rectValue,nil];
id currentVal = [params1 objectAtIndex:0];
NSInteger i=2;
if ([currentVal isKindOfClass:[NSValue class]]) {
    void *bufferForValue;
    [currentVal getValue:&bufferForValue];
    [anInvocation1 setArgument:&bufferForValue atIndex:i];
}else {
    [anInvocation1 setArgument:&currentVal atIndex:i];
}
[anInvocation1 invoke];

当此(getValue:)方法实现'i'的值时，其值从2变为1130102784，在(setArgument:atIndex:)中，我有了一个SIGABRT，因为索引i超出范围.

When this(getValue:) method implements value of 'i' changes from 2 to something like : 1130102784, and in (setArgument:atIndex:) I have an SIGABRT because index i is out of bounds.

那为什么[NSValue getValue:(*void) buffer]会更改其他变量?

So why does [NSValue getValue:(*void) buffer] change other variables?

(P.S.我在函数中执行此操作，因此我简化了示例并直接初始化数组.如果我直接设置atIndex:2，它会完美.但是，由于我很难过，我简化了一点，我需要将我传递给atIndex:)

(P.S. I do it in function so I simplified an example and initialize array directly.And if I set directly atIndex:2, It works perfect.But as I've sad I simplified a little, and I need to pass i to atIndex:)

感谢汤姆·达林(特别是)，塞尔吉奥问题得以解决.我删除了这个:

Thanks to Tom Dalling(especially) and sergio problem solved. I delete this:

void *bufferForValue;
[currentVal getValue:&bufferForValue];
[anInvocation1 setArgument:&bufferForValue atIndex:i];

并粘贴

NSUInteger bufferSize = 0;
NSGetSizeAndAlignment([currentVal objCType], &bufferSize, NULL);
void* buffer = malloc(bufferSize);
[currentVal getValue:buffer];
[anInvocation1 setArgument:buffer atIndex:i];

谢谢. Stackoverflow.com对聪明的人很有帮助.

Thank you. Stackoverflow.com really helpful site with smart people.

推荐答案

您不能将NSRect放入void*中.正确的代码是:

You can't fit an NSRect into a void*. The correct code would be:

NSRect buffer;
[currentVal getValue:&buffer];

或者，如果您不知道NSValue对象的内容，则:

Or alternatively, if you don't know the contents of the NSValue object:

NSUInteger bufferSize = 0;
NSGetSizeAndAlignment([currentVal objCType], &bufferSize, NULL);
void* buffer = malloc(bufferSize);
[currentVal getValue:buffer]; //notice the lack of '&'
//do something here
free(buffer);

i的值正在更改，因为您的代码导致其他堆栈分配的变量溢出.

The value for i is changing because your code causes an overflow into other stack-allocated variables.

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