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Objective-C中調(diào)用函數(shù)的方法是“消息傳遞”，這個(gè)和普通的函數(shù)調(diào)用的區(qū)別是，你可以隨時(shí)對(duì)一個(gè)對(duì)象傳遞任何消息，而不需要在編譯的時(shí)候聲明這些方法。所以O(shè)bjective-C可以在runtime的時(shí)候傳遞人和消息。
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首先介紹兩個(gè)方法 SEL和@selector
根據(jù)Apple Objective-C Runtime Reference 官方文檔這個(gè)傳遞消息的函數(shù)就是? id ?objc_msgSend( id? theReceiver,? SEL theSelector, …)
theReceiver是接受消息的對(duì)象類型是id，theSelector是消息名稱類型是SEL。下邊代碼我們來看看如何來生成一個(gè)SEL，如果傳遞消息。
- ( void ) fooNoInputs {
NSLog( @"Does nothing" );
}
然后調(diào)用它
[ self ?performSelector: @selector (fooNoInputs)];
第二個(gè)試驗(yàn)看看如何在消息中傳遞參數(shù)
我們建立一個(gè)有input參數(shù)的函數(shù)
- ( void ) fooOneIput:(NSString*) first {
NSLog( @"Logs %@" , first);
}
然后調(diào)用它
[ self ?performSelector: @selector (fooOneInput:) withObject: @"first" ];
第三個(gè)試驗(yàn)更多的參數(shù)
- ( void ) fooFirstInput:(NSString*) first secondInput:(NSString*) second {
NSLog( @"Logs %@ then %@" , first, second);
}
然后調(diào)用它
[ self ?performSelector: @selector (fooFirstInput:secondInput:) withObject: @"first" withObject: @"second" ];
第四個(gè)試驗(yàn)如何建立動(dòng)態(tài)的函數(shù)，然后調(diào)用他們？我們需要建立一個(gè)selector
SEL ?myTestSelector =? @selector (myTest:);
并且我們調(diào)用的函數(shù)在另外一個(gè)Class內(nèi)
- ( 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會(huì)產(chǎn)生“performSelector may cause a leak because its selector is unknown”警告
2.這種方式當(dāng)傳入一個(gè)不符合約定的消息時(shí)會(huì)繼續(xù)運(yùn)行并不報(bào)錯(cuò)。例如應(yīng)該傳入2個(gè)參數(shù)，但只傳入1個(gè)參數(shù)。或傳入了3個(gè)參數(shù)，第三個(gè)參數(shù)不會(huì)被初始化。還有一種調(diào)用其他Class Function的方法是，但是不能有參數(shù)，我們這里假設(shè)沒有參數(shù)，那么就可以這樣
[mfs?customSelector];?
完整的代碼：
@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);
}
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- ( NSArray ?* )abcWithAAA: ( NSNumber ?*)number {
int ?primaryKey = [number? intValue ];
NSLog ( "%i" , primaryKey);
}
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- ( void ) performMethodsViaSelectors {
[ self ?performSelector: @selector (fooNoInputs)];
[ self ?performSelector: @selector (fooOneInput:) withObject: @"first" ];
[ self ?performSelector: @selector (fooFirstInput:secondInput:) withObject: @"first" withObject: @"second" ];
}
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- ( 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
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