Objective-C中一种消息处理方法performSelector: withObject:

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