OC获取UITextField的成员变量的方法
#import <objc/runtime.h>
unsigned int count;
Ivar *ivarList = class_copyIvarList([UITextField class], &count);
for (int i=0; i< count; i++) {
Ivar ivar = ivarList[i];
NSLog(@"%s",ivar_getName(ivar));
}
free(ivarList);