NSMethodSignature和NSInvocation的用法

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1.   

NSMethodSignature顾名思义应该就是“方法签名”，类似于C++中的编译器时的函数签名。

官方定义该类为对方法的参数、返回类似进行封装，协同NSInvocation实现消息转发。

通过消息转发可以用B实现A的方法。也是一种多重继承的解决方法。

<p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"><span class="kwd" style="color: rgb(0, 0, 136);">interface</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">LOCBird</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSObject</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSString</span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln"> name_</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln">    </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="lit" style="color: rgb(0, 102, 102);">@end</span><span class="lit" style="color: rgb(0, 102, 102);">@implementation</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">LOCBird</span><span class="pun" style="color: rgb(102, 102, 0);">-</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln">id</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln">init</span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">self</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="kwd" style="color: rgb(0, 0, 136);">super</span><span class="pln"> init</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">if</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">self</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln">  name_ </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[[</span><span class="typ" style="color: rgb(102, 0, 102);">NSString</span><span class="pln"> alloc</span><span class="pun" style="color: rgb(102, 102, 0);">]</span><span class="pln"> initWithString</span><span class="pun" style="color: rgb(102, 102, 0);">:@</span><span class="str" style="color: rgb(0, 136, 0);">"I am a Bird!!"</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">  </span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">self</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pun" style="color: rgb(102, 102, 0);">-</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">void</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln">dealloc</span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">name_ release</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="kwd" style="color: rgb(0, 0, 136);">super</span><span class="pln"> dealloc</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pun" style="color: rgb(102, 102, 0);">-</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="typ" style="color: rgb(102, 0, 102);">NSMethodSignature</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">*)</span><span class="pln">methodSignatureForSelector</span><span class="pun" style="color: rgb(102, 102, 0);">:(</span><span class="pln">SEL</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln">aSelector</span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSMethodSignature</span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln"> signature </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="kwd" style="color: rgb(0, 0, 136);">super</span><span class="pln"> methodSignatureForSelector</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">aSelector</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">if</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln">signature</span><span class="pun" style="color: rgb(102, 102, 0);">==</span><span class="kwd" style="color: rgb(0, 0, 136);">nil</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln">  signature </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">name_ methodSignatureForSelector</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">aSelector</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSUInteger</span><span class="pln"> argCount </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">signature numberOfArguments</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">for</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="typ" style="color: rgb(102, 0, 102);">NSInteger</span><span class="pln"> i</span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="lit" style="color: rgb(0, 102, 102);">0</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln"> i</span><span class="pun" style="color: rgb(102, 102, 0);"><</span><span class="pln">argCount </span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln"> i</span><span class="pun" style="color: rgb(102, 102, 0);">++)</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln">  </span><span class="typ" style="color: rgb(102, 0, 102);">NSLog</span><span class="pun" style="color: rgb(102, 102, 0);">(@</span><span class="str" style="color: rgb(0, 136, 0);">"%s"</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">signature getArgumentTypeAtIndex</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">i</span><span class="pun" style="color: rgb(102, 102, 0);">]);</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSLog</span><span class="pun" style="color: rgb(102, 102, 0);">(@</span><span class="str" style="color: rgb(0, 136, 0);">"returnType:%s ,returnLen:%d"</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">signature methodReturnType</span><span class="pun" style="color: rgb(102, 102, 0);">]</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">signature methodReturnLength</span><span class="pun" style="color: rgb(102, 102, 0);">]);</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSLog</span><span class="pun" style="color: rgb(102, 102, 0);">(@</span><span class="str" style="color: rgb(0, 136, 0);">"signature:%@"</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> signature</span><span class="pun" style="color: rgb(102, 102, 0);">);</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln"> signature</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pun" style="color: rgb(102, 102, 0);">-</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">void</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln">forwardInvocation</span><span class="pun" style="color: rgb(102, 102, 0);">:(</span><span class="typ" style="color: rgb(102, 0, 102);">NSInvocation</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">*)</span><span class="pln">anInvocation</span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSLog</span><span class="pun" style="color: rgb(102, 102, 0);">(@</span><span class="str" style="color: rgb(0, 136, 0);">"forwardInvocation:%@"</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> anInvocation</span><span class="pun" style="color: rgb(102, 102, 0);">);</span><span class="pln"> SEL seletor </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">anInvocation selector</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">if</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">([</span><span class="pln">name_ respondsToSelector</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">seletor</span><span class="pun" style="color: rgb(102, 102, 0);">])</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln">  </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">anInvocation invokeWithTarget</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">name_</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="lit" style="color: rgb(0, 102, 102);">@end</span></p><p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"></p><p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"><span class="com" style="color: rgb(136, 0, 0);">//调用</span></p><p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"><span class="com" style="color: rgb(136, 0, 0);"> id bird = [[LOCBird alloc] init];</span><span class="pln"> </span><span class="typ" style="color: rgb(102, 0, 102);">NSLog</span><span class="pun" style="color: rgb(102, 102, 0);">(@</span><span class="str" style="color: rgb(0, 136, 0);">"len= %d"</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">bird length</span><span class="pun" style="color: rgb(102, 102, 0);">]);</span></p>

输出 参考

表 6-1  Objective-C类型编码

编码

含义

c

char

i

int

s

short

l

long

在64位程序中，l为32位。

q

long long

C

unsigned char

I

unsigned int

S

unsigned short

L

unsigned long

Q

unsigned long long

f

float

d

double

B

C++标准的bool或者C99标准的_Bool

v

void

*

字符串（char *）

@

对象（无论是静态指定的还是通过id引用的）

#

类（Class）

:

方法选标（SEL）

[array type]

数组

{name=type...}

结构体

(name=type...)

联合体

bnum

num个bit的位域

^type

type类型的指针

?

未知类型（其它时候，一般用来指函数指针）

使用方法

<p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"><span class="pun" style="color: rgb(102, 102, 0);">-(</span><span class="kwd" style="color: rgb(0, 0, 136);">void</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln"> initWithTarget</span><span class="pun" style="color: rgb(102, 102, 0);">:(</span><span class="pln">id</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln"> rec selector</span><span class="pun" style="color: rgb(102, 102, 0);">:(</span><span class="pln">SEL</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln"> cb</span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln">    anchorPoint_ </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> ccp</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="lit" style="color: rgb(0, 102, 102);">0.5f</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">0.5f</span><span class="pun" style="color: rgb(102, 102, 0);">);</span><span class="pln">    </span><span class="typ" style="color: rgb(102, 0, 102);">NSMethodSignature</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln"> sig </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">nil</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln">    </span><span class="kwd" style="color: rgb(0, 0, 136);">if</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln"> rec </span><span class="pun" style="color: rgb(102, 102, 0);">&&</span><span class="pln"> cb </span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln">        sig </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">rec methodSignatureForSelector</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">cb</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">        invocation </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">nil</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln">        invocation </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="typ" style="color: rgb(102, 0, 102);">NSInvocation</span><span class="pln"> invocationWithMethodSignature</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">sig</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">        </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">invocation setTarget</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">rec</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">        </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">invocation setSelector</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln">cb</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">        </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">invocation setArgument</span><span class="pun" style="color: rgb(102, 102, 0);">:&</span><span class="kwd" style="color: rgb(0, 0, 136);">self</span><span class="pln"> atIndex</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="lit" style="color: rgb(0, 102, 102);">2</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">        </span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln">invocation retain</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln">    </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pun" style="color: rgb(102, 102, 0);">}</span></p>

当 [invocation invoke];是调用SEL。上述第二个参数为自身。

用NSMethodSignature和NSInvocation实现编码

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1. - (void)encodeWithCoder:(NSCoder *)encoder{  
2.     NSDictionary *attrDic = [self getKeyAndObjectForDictionry];  
3.     if (attrDic == nil) {  
4.         return;  
5.     }  
6.     NSEnumerator *keyEnum = [attrDic keyEnumerator];  
7.     id attributeName;  
8.     while ((attributeName = [keyEnum nextObject])) {  
9.         SEL getSel = NSSelectorFromString(attributeName);  
10.         if ([self respondsToSelector:getSel]) {  
11.             NSMethodSignature *signature = nil;  
12.             signature = [self methodSignatureForSelector:getSel];  
13.             NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];  
14.             [invocation setTarget:self];  
15.             [invocation setSelector:getSel];  
16.             NSObject *valueObj = nil;  
17.             [invocation invoke];  
18.             [invocation getReturnValue:&valueObj];  
19.               
20.             if (valueObj) {  
21.                 [encoder encodeObject:valueObj forKey:attributeName];  
22.             }  
23.         }  
24.     }  
25. }