iOS面接集錦

1.OC言語のメリットとデメリット
メリット:

category

posing

動特性runtime:関数はIMP動的バインディングを実現し、resolve

指標計算

フレックスメッセージ伝達

は複雑すぎるC派生言語ではありません

Objective_CとC++は混成することができる;欠点:

は、メタネーミングスペース

をサポートしていません.

演算子リロード

はサポートされていません.

多重継承

はサポートされていない.

動的ランタイムタイプを使用し、すべての方法は関数呼び出しであり、多くのコンパイル時最適化スキームは、インライン関数などの使用できず、パフォーマンスが劣っています.

2.OCメッセージ送信メカニズム

    // 1.    
    ViewController *VC = [ViewController new];
    [VC testCommand];
    
    // 2.   objc_msgSend     
    ViewController *VC1 = ((ViewController *(*)(id, SEL))objc_msgSend)([ViewController class], @selector(alloc));
    VC1 = ((ViewController *(*)(id, SEL))objc_msgSend)(VC1, @selector(init));
    ((ViewController *(*)(id, SEL))objc_msgSend)(VC1, @selector(testCommand));
    
    // 3.    performSelector map   
    [VC performSelector:@selector(testCommand) withObject:@"132"];

3.OCメッセージ転送メカニズム

@interface ADDIMP :NSObject
- (void)testCommand1;
@end

@implementation ADDIMP
- (void)testCommand1 {
    NSLog(@"%s
     IMP ", __FUNCTION__);
}
@end

@interface ViewController ()
 //        ,         
- (void)testCommand1;
@end

@implementation ViewController
//       IMP
void dynamicMethodIMP(id self, SEL _cmd)
{
    printf("%s", __func__);
}

// 1.       ,    runtime      IMP
+ (BOOL)resolveInstanceMethod:(SEL)sel {
    NSLog(@"sel =%@", NSStringFromSelector(sel));
//    if (sel == NSSelectorFromString(@"testCommand1")) {
//        NSLog(@"%s
       IMP ", __FUNCTION__);
//        class_addMethod(self, sel, (IMP)dynamicMethodIMP, "v@:");
//        return YES;
//    }
    return [super resolveInstanceMethod:sel];
}

// 2.       
- (id)forwardingTargetForSelector:(SEL)aSelector {
    NSLog(@"%s
      IMP ", __FUNCTION__);
    
//    if (aSelector == NSSelectorFromString(@"testCommand1")){
//
//        return [ADDIMP new];
//    }
    return [super forwardingTargetForSelector:aSelector];
 
}

// 3.        
// 3.1     
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    if (aSelector == NSSelectorFromString(@"testCommand1")){
        NSMethodSignature *sign = [NSMethodSignature signatureWithObjCTypes:"v@:"];
        return sign;
    }
    return [super methodSignatureForSelector:aSelector];
}

// 3.2     
- (void)forwardInvocation:(NSInvocation *)anInvocation {
    SEL aSelector = [anInvocation selector];
    
    ADDIMP *add = [ADDIMP new];
    if ([add respondsToSelector:aSelector])
        [anInvocation invokeWithTarget:add];
    else
        [super forwardInvocation:anInvocation];
}
 
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    [self testCommand1];
}
@end

4.OCシミュレーション多重継承
//SubClass.h

#import 

@protocol ClassOne_protocol
- (void)ClassOneString:(NSString *)string;
@end

@interface ClassOne : NSObject 

@end

@protocol ClassTwo_protocol
- (void)ClassTwoString:(NSString *)string;
@end
@interface ClassTwo : NSObject

@end

@interface SubClass : NSProxy 
+ (instancetype)subClass;
@end

//SubClass.m

#import "SubClass.h"
#import 
 
@implementation ClassOne
- (void)ClassOneString:(NSString *)string {
    NSLog(@"
%s
 ClassOneString
", __FUNCTION__);
}
@end
 
@implementation ClassTwo
- (void)ClassTwoString:(NSString *)string {
    NSLog(@"
%s
 ClassTwoString
", __FUNCTION__);
}
@end
 
@implementation SubClass{
    NSMutableDictionary *_methodMap;
}

+ (instancetype)subClass {
    return [[SubClass alloc] init];
}

- (instancetype)init { 
    _methodMap = [NSMutableDictionary dictionary];
    
    [self registerMethodsWithTarget:[ClassOne new]];
    [self registerMethodsWithTarget:[ClassTwo new]];
    
    return self;
}

- (void)registerMethodsWithTarget:(id)target {
    unsigned int count = 0;
    
    //       
    Method *methodList = class_copyMethodList([target class], &count);
    
    //       
    for (NSInteger i = 0; i < count; i++) {
        
        Method method = methodList[i];
        
        SEL sel = method_getName(method);
        [_methodMap setObject:target forKey:NSStringFromSelector(sel)];
    }
    
    // dealloc      
    free(methodList);
}
 
//          ,       
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    
    // 1.      
    NSString *methodName = NSStringFromSelector(aSelector);
    
    // 2.       
    id target = [_methodMap objectForKey:methodName];
    
    // 3.        
    if(target && [target respondsToSelector:aSelector]) {
        return [target methodSignatureForSelector:aSelector];
    }
    return [super methodSignatureForSelector:aSelector];
}

//     
- (void)forwardInvocation:(NSInvocation *)anInvocation {
    SEL sel = anInvocation.selector;
    NSString *methodName = NSStringFromSelector(sel);
    id target = [_methodMap objectForKey:methodName];
    
    if (target && [target respondsToSelector:sel]) {
        //   
        [anInvocation invokeWithTarget:target];
    }else
    [super forwardInvocation:anInvocation];
}

@end

//テスト

   SubClass *subClass = [SubClass subClass]; 
   [subClass ClassOneString:@"111111111"];
   [subClass ClassTwoString:@"222222222"];