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Apple Objective-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。
- ( 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 ([ NSString stringWithFormat : @"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 ([ NSString stringWithFormat : @"abcWith%@:" , array]);
mfs = [[ MethodForSelectors alloc ] performSelector :customSelector withObject :0];
}
}
@end
@implementation MethodForSelectors- ( void )abcWithAAA: ( NSNumber *)number {
NSLog ( "%i" , number);
}
@end
