【Objective-C Runtime動態載入】---動態創建類Class

動態創建類Class,動態添加Class成員變數與成員函數,動態變數賦值與取值，動態函數調用等方法

a.使用objc_allocateClassPair創建一個類Class
    const char * className = "Calculator";
    Class kclass = objc_getClass(className);
    if (!kclass) 
    {
       Class superClass = [NSObject class]; 
       kclass = objc_allocateClassPair(superClass, className, 0);
    }

b.使用class_addIvar添加一個成員變數
    NSUInteger size;
    NSUInteger alignment;
    NSGetSizeAndAlignment("*", &size, &alignment);
    class_addIvar(kclass, "expression", size, alignment, "*");


    註:
    1.type定義參考:https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html
    2."*"星號代表字元(),iOS字元為4位，並採用4位對齊kclass

c.使用class_addMethod添加成員方法
    class_addMethod(kclass, @selector(setExpressionFormula:), (IMP)setExpressionFormula, "v@:@");
    class_addMethod(kclass, @selector(getExpressionFormula), (IMP)getExpressionFormula, "@@:");

    static void setExpressionFormula(id self, SEL cmd, id value)
    {
       NSLog(@"call setExpressionFormula");
    }

    static void getExpressionFormula(id self, SEL cmd)
    {
        NSLog(@"call getExpressionFormula");
    } 

    註:
    1.type定義參考:https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html
    2."v@:@",解釋v-返回值void類型,@-self指針id類型,:-SEL指針SEL類型,@-函數第一個參數為id類型
    3."@@:",解釋@-返回值id類型,@-self指針id類型,:-SEL指針SEL類型,
d.註冊到運行時環境
    objc_registerClassPair(kclass);
e.實例化類
    id instance = [[kclass alloc] init];
f.給變數賦值
   object_setInstanceVariable(instance, "expression", "1+1"); 
g.獲取變數值
    void * value = NULL;
    object_getInstanceVariable(instance, "expression", &value); 
h.調用函數
    [instance performSelector:@selector(getExpressionFormula)];