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技術社區[雲棲]
obj-c編程06:反射與元編程初步
我們知道對於現如今的動態語言比如ruby而言，反射和元編程以及支持的非常靈活了，你完全可以跳過常規的手段，而利用反射來查詢或調用對象的私有方法。而obj-c對反射的支持略顯小繁瑣，而且在開了ARC後同樣出錯。就算不開ARC，為啥明明有那個方法卻不能調用呢？為啥double變量不讓直接轉成id呢？蛋疼啊，上代碼：
#import <Foundation/Foundation.h>
@interface A:NSObject{
double i;
}
@property double i;
-(double)mul:(double)x;
-(void)show;
@end
@implementation A
@synthesize i;
-(double)mul:(double)x{
return i * x;
}
-(void)show{
NSLog(@"[A obj]i : %f",i);
}
@end
@interface B:NSObject{
int i;
}
@property int i;
-(int)mul:(int)x;
-(void)show;
@end
@implementation B
@synthesize i;
-(int)mul:(int)x{
return i * x;
}
-(void)show{
NSLog(@"[B obj]i : %d",i);
}
@end
int main(int argc,char *argv[])
{
@autoreleasepool{
NSLog(@"hello obj-c!");
id obj = [[A alloc] init];
if([obj respondsToSelector: @selector(setI:)])
[obj performSelector: @selector(setI:) withObject:(id)(int)99.99];
[obj show]; //why show can exec???
SEL action_mul = @selector(mul);
SEL action_i = @selector(i);
if([obj respondsToSelector: action_mul] && [obj respondsToSelector: action_i])
NSLog(@"%f * %f is %f",[obj respondsToSelector :action_i],99.99,[obj respondsToSelector: action_mul]);
}
return 0;
}
不能開ARC，編譯運行如下：
apple@kissAir: objc_src$clang -framework Foundation 2.m -o 2
2.m:58:27: warning: format specifies type 'double' but the argument has type
'BOOL' (aka 'signed char') [-Wformat]
...NSLog(@"%f * %f is %f",[obj respondsToSelector :action_i],99.99,[obj resp...
~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
%hhd
2.m:58:68: warning: format specifies type 'double' but the argument has type
'BOOL' (aka 'signed char') [-Wformat]
...%f",[obj respondsToSelector :action_i],99.99,[obj respondsToSelector: action_mul]);
~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
%hhd
2 warnings generated.
apple@kissAir: objc_src$./2
2014-06-30 09:27:33.968 2[1010:507] hello obj-c!
2014-06-30 09:27:33.970 2[1010:507] [A obj]i : 0.000000
很明顯沒有執行方法！為啥呢，不知道啊！
最後更新：2017-04-03 06:03:10