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Objective-C performSelector: withObject: 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=@selector(@"`.......");
 
SEL customSelector = NSSelectorFromString([NSStringstringWithFormat:@"abcWith%@:", array]);
 
mfs = [[MethodForSelectors alloc] performSelector:customSelector withObject:0];
 
}
 
 
 
 
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
 
 
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