Objective-C中一种消息处理方法performSelector: withObject:_objective-c 方法中animated:yes-优快云博客

今天在使用HUD的时候遇到了一个参数传递的问题，因为自己写的识别的代码需要传递一个参数，纠结如何传递这个image

这是自己的方法

-(void)DetectFace:(UIImage*)userImage

于是引发了一系列对@selector的知识的不了解，在网上找到了一篇不错的文章一会详细的贴在下文

    [HUD showWhileExecuting:@selector(myMixedTask) onTarget:self withObject:nil animated:YES];

解决办法即可转载原文

[HUD showWhileExecuting:@selector(DetectFace:) onTarget:self withObject:image.image animated:YES]

Objective-C中调用函数的方法是“消息传递”，这个和普通的函数调用的区别是，你可以随时对一个对象传递任何消息，而不需要在编译的时候声明这些方法。所以Objective-C可以在runtime的时候传递人和消息。

首先介绍两个方法 SEL和@selector

根据AppleObjective-C Runtime Reference官方文档这个传递消息的函数就是 id objc_msgSend(id theReceiver, SEL theSelector, …)

theReceiver是接受消息的对象类型是id，theSelector是消息名称类型是SEL。下边代码我们来看看如何来生成一个SEL，如果传递消息。

首先建立一个简单的函数

- (void) fooNoInputs {

NSLog(@"Does nothing");

}

然后调用它

[self performSelector:@selector(fooNoInputs)];

第二个试验看看如何在消息中传递参数

我们建立一个有input参数的函数

- (void) fooOneIput:(NSString*) first {

NSLog(@"Logs %@", first);

}

然后调用它

[self performSelector:@selector(fooOneInput:) withObject:@"first"];

第三个试验更多的参数

- (void) fooFirstInput:(NSString*) first secondInput:(NSString*) second {

NSLog(@"Logs %@ then %@", first, second);

}

然后调用它

[self performSelector:@selector(fooFirstInput:secondInput:) withObject:@"first"withObject:@"second"];

第四个试验如何建立动态的函数，然后调用他们？我们需要建立一个selector

SEL myTestSelector = @selector(myTest:);

并且我们调用的函数在另外一个Class内

- (void)abcWithAAA: (NSNumber *)number {

int primaryKey = [number intValue];

NSLog("%i", primaryKey);

}

MethodForSelectors * mfs = [[MethodForSelectors alloc]init];

NSArray *Arrays = [NSArray arrayWithObjects:@"AAA", @"BBB", nil];

for ( NSString *array in Arrays ){

SEL customSelector = NSSelectorFromString([NSStringstringWithFormat:@"abcWith%@:", array]);

mfs = [[MethodForSelectors alloc] performSelector:customSelector withObject:0];

}

注意：updated at 20120606

1.如果使用了ARC会产生“performSelector may cause a leak because its selector is unknown”警告
2.这种方式当传入一个不符合约定的消息时会继续运行并不报错。例如应该传入2个参数，但只传入1个参数。或传入了3个参数，第三个参数不会被初始化。

还有一种调用其他Class Function的方法是，但是不能有参数，我们这里假设没有参数，那么就可以这样

[mfs customSelector];

完整的代码：

@implementation ClassForSelectors
- (void) fooNoInputs {

NSLog(@"Does nothing");

}

- (void) fooOneIput:(NSString*) first {

NSLog(@"Logs %@", first);

}

- (void) fooFirstInput:(NSString*) first secondInput:(NSString*) second {

NSLog(@"Logs %@ then %@", first, second);

}

- (NSArray *)abcWithAAA: (NSNumber *)number {

int primaryKey = [number intValue];

NSLog("%i", primaryKey);

}

- (void) performMethodsViaSelectors {

[self performSelector:@selector(fooNoInputs)];

[self performSelector:@selector(fooOneInput:) withObject:@"first"];

[self performSelector:@selector(fooFirstInput:secondInput:) withObject:@"first"withObject:@"second"];

}

- (void) performDynamicMethodsViaSelectors {

MethodForSelectors * mfs = [MethodForSelectors alloc];

NSArray *Arrays = [NSArray arrayWithObjects:@"AAA", @"BBB", nil];

for ( NSString *array in Arrays ){

SEL customSelector = NSSelectorFromString([NSStringstringWithFormat:@"abcWith%@:", array]);

mfs = [[MethodForSelectors alloc] performSelector:customSelector withObject:0];

}

}

@end

@implementation MethodForSelectors

- (void)abcWithAAA: (NSNumber *)number {

NSLog("%i", number);

}

@end

--EOF--

作者：Buro#79xxd 出处：http://www.cnblogs.com/buro79xxd/ 文章版权归本人所有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。

http://stackoverflow.com/questions/932801/how-to-i-pass-selector-as-a-parameter

The problem here isn't passing a selector to a method, per se, but passing a selector where an object is expected. To pass a non-object value as an object, you can use NSValue. In this case, you'll need to create a method that accepts an NSValue and retrieves the appropriate selector. Here's an example implementation:

@implementation Thing
- (void)method:(SEL)selector {
    // Do something
}

- (void)methodWithSelectorValue:(NSValue *)value {
    SEL selector;

    // Guard against buffer overflow
    if (strcmp([value objCType], @encode(SEL)) == 0) {
        [value getValue:&selector];
        [self method:selector];
    }
}

- (void)otherMethodShownInYourExample {
    SEL selector = @selector(something);
    NSValue *selectorAsValue = [NSValue valueWithBytes:&selector objCType:@encode(SEL)];
    [NSThread detachNewThreadSelector:@selector(methodWithSelectorValue:) toTarget:self withObject:selectorAsValue];
}
@end