【知识总结】写法

1,默认的初始化数据，在初始化方法中进行设置

比如：NSInterge _selectedIndex;
默认情况下设置为 _selectedIndex = 1；
如果在 viewDidload 方法中进行默认是的设置 ，外界在设置 _selectedIndex = 2 的时机在 viewDidload 之前，则这次的设置就会被重置为 1。

因此，初始化的默认值推荐在初始化中进行设置

---

XMNetworking

2，队列写法

static dispatch_queue_t xm_request_completion_callback_queue() {
    static dispatch_queue_t _xm_request_completion_callback_queue;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _xm_request_completion_callback_queue = dispatch_queue_create("com.xmnetworking.request.completion.callback.queue", DISPATCH_QUEUE_CONCURRENT);
    });
    return _xm_request_completion_callback_queue;
}

上面的这种书写方式，便于之后的队列调用，如：

dispatch_async(xm_request_completion_callback_queue(), ^{
                completionHandler(nil, serializationError);
            });

3，信号量：使用宏定义

dispatch_semaphore_t _lock;
_lock = dispatch_semaphore_create(1);

#define XMLock() dispatch_semaphore_wait(self->_lock, DISPATCH_TIME_FOREVER)
#define XMUnlock() dispatch_semaphore_signal(self->_lock)

4，block 使用 宏 调用

#define XM_SAFE_BLOCK(BlockName, ...) ({ !BlockName ? nil : BlockName(__VA_ARGS__); })

// 调用：
XM_SAFE_BLOCK(self.requestProcessHandler, request);

---

AOP 中的方法替换写法：

+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        
        SEL originalSelector = @selector(setCachePolicy:);
        SEL swizzledSelector = @selector(ag_setCachePolicy:);
        
        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
        
        BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        if (success) {
            class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

多个方法需要替换，可以使用下面方式

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSArray *selStringsArray = @[@"reloadData", @"reloadRowsAtIndexPaths:withRowAnimation:", @"deleteRowsAtIndexPaths:withRowAnimation:", @"insertRowsAtIndexPaths:withRowAnimation:"];
        [selStringsArray enumerateObjectsUsingBlock:^(NSString *selString, NSUInteger idx, BOOL *stop) {
            NSString *mySelString = [@"sd_" stringByAppendingString:selString];
            
            Method originalMethod = class_getInstanceMethod(self, NSSelectorFromString(selString));
            Method myMethod = class_getInstanceMethod(self, NSSelectorFromString(mySelString));
            method_exchangeImplementations(originalMethod, myMethod);
        }];
    });
}