iOS_Runtime是什么？原理？作用？怎么实现weak？使用
iOS_Runtime是什么？原理？作用？怎么实现weak？使用
mikimo
发布于 2022-07-20 14:11:56
发布于 2022-07-20 14:11:56
Runtime：
1、什么是runtime？
就是在程序运行的过程中，有一套C语言级别的API，它把代码从OC转换成C
2、原理：
OC是基于C，并添加了面向对象的特性，将很多静态语言在编译和链接时做的事放到了runtime运行时来处理
C：函数的调用在编译时就知道会调用哪个函数
OC：在编译的时候并不知道，只在正在运行时才会根据函数名称找到对应的函数
3、作用
获取属性、方法、成员变量、协议（包括私有的）
给分类动态添加属性、方法
字典转模型
拦截并替换方法
实现NSCoding的归档和反归档
4、Runtime是怎么实现weak？(我有在一次面试中遇到)
Runtime对注册的类会进行布局，对于weak对象会放入一个hash表中，用weak指向的`对象的内存地址`作为key。当对象的引用计数为0时会调用dealloc方法，此时会在weak表中搜索，将所有weak对象置为nil。
Key：对象内存地址 — value：n个weak对象
5、使用
- 替换ViewController生命周期方法
- 解决获取索引、添加、删除元素越界crash问题
- 防止按钮重复暴力点击
- 全局更换控件初始效果
- App热修复
- App异常加载占位图通用类封装
- 全局修改导航栏返回按钮 (去掉title)
以下是使用内容：
- `NSObject`的`Category`里实现方法替换，方便需要的类直接调用：
// NSObject+Swizzling.h
+ (void)methodSwizzlingWithOriginalSelector:(SEL)originalSelector bySwizzledSelector:(SEL)swizzledSelector;
// NSObject+Swizzling.m
+ (void)methodSwizzlingWithOriginalSelector:(SEL)originalSelector bySwizzledSelector:(SEL)swizzledSelector {
Class class = [self class];
// 原有方法
Method originalMethod = class_getInstanceMethod(class, originalSelector);
// 新方法
Method swizzledMetod = class_getInstanceMethod(class, swizzledSelector);
// 尝试添加`origin`方法
BOOL didAddMethod = class_addMethod(class,
originalSelector,
method_getImplementation(swizzledMetod),
method_getTypeEncoding(swizzledMetod));
if (didAddMethod) { // 之前没有实现`origin`方法
class_replaceMethod(class,
swizzledSelector,
method_getImplementation(originalMethod),
method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMetod);
}
}- `UINavigationController`的`Category`里替换相应的方法，并添加需要的处理
// UIViewController+Swizzling.m
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self methodSwizzlingWithOriginalSelector:@selector(viewWillDisappear:) bySwizzledSelector:@selector(mo_viewWillDisappear:)];
});
}
- (void)mo_viewWillDisappear:(BOOL)animated {
[self mo_viewWillDisappear:animated];
// 添加埋点等
}- `NSMutableArray`的`Category`里拦截增删改方法，进行判空处理 （其他的NSArray、NSDictionary、NSMutableArray、NSMutableDictionary等也可以做相应的处理，防止越界crash）
- 类 真身 NSArray __NSArrayI NSMutableArray __NSArrayM NSDictionary __NSDictionaryI NSMutableDictionary __NSDictionaryM
// NSMutableArray+Swizzling.m
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// objc_getClass("__NSArrayM") 没有用 [self class] 处理，是因为运行时用了`类簇` 运行时正在的类是前者
[objc_getClass("__NSArrayM") methodSwizzlingWithOriginalSelector:@selector(addObject:) bySwizzledSelector:@selector(safeAddObject:)];
[objc_getClass("__NSArrayM") methodSwizzlingWithOriginalSelector:@selector(insertObject:atIndex:) bySwizzledSelector:@selector(safeInsertObject:atIndex:)];
[objc_getClass("__NSArrayM") methodSwizzlingWithOriginalSelector:@selector(objectAtIndex:) bySwizzledSelector:@selector(safeObjectAtIndex:)];
[objc_getClass("__NSArrayM") methodSwizzlingWithOriginalSelector:@selector(removeObjectAtIndex:) bySwizzledSelector:@selector(safeRemoveObjectAtIndex:)];
[objc_getClass("__NSArrayM") methodSwizzlingWithOriginalSelector:@selector(removeObject:) bySwizzledSelector:@selector(safeRemoveObject:) ];
});
}
- (void)safeAddObject:(id)obj {
if (obj == nil) {
NSLog(@"%s can add nil object into NSMutableArray", __FUNCTION__);
} else {
[self safeAddObject:obj];
}
}
- (void)safeRemoveObject:(id)obj {
if (obj == nil) {
NSLog(@"%s call -removeObject:, but argument obj is nil", __FUNCTION__);
return;
}
[self safeRemoveObject:obj];
}
- (void)safeInsertObject:(id)anObject atIndex:(NSUInteger)index {
if (anObject == nil) {
NSLog(@"%s can't insert nil into NSMutableArray", __FUNCTION__);
} else if (index > self.count) {
NSLog(@"%s index is invalid", __FUNCTION__);
} else {
[self safeInsertObject:anObject atIndex:index];
}
}
- (id)safeObjectAtIndex:(NSUInteger)index {
if (self.count == 0) {
NSLog(@"%s can't get any object from an empty array", __FUNCTION__);
return nil;
}
if (index > self.count) {
NSLog(@"%s index out of bounds in array", __FUNCTION__);
return nil;
}
return [self safeObjectAtIndex:index];
}
- (void)safeRemoveObjectAtIndex:(NSUInteger)index {
if (self.count <= 0) {
NSLog(@"%s can't get any object from an empty array", __FUNCTION__);
return;
}
if (index >= self.count) {
NSLog(@"%s index out of bound", __FUNCTION__);
return;
}
[self safeRemoveObjectAtIndex:index];
}- UIButton的Category中替换 sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event 改用 afterDelay 调用，并添加标志位，防止暴力点击，具体代码如下：
// UIButton+Swizzling.m
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self methodSwizzlingWithOriginalSelector:@selector(sendAction:to:forEvent:) bySwizzledSelector:@selector(mo_sendAction:to:forEvent:)];
});
}
// 当按钮点击事件 sendAction 时将会执行 mo_sendAction
- (void)mo_sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
if (self.isIgnore) { // 不需要被hook
[self mo_sendAction:action to:target forEvent:event];
return;
}
if ([NSStringFromClass(self.class) isEqualToString:@"UIButton"]) {
if (self.isIgnoreEvent) {
return;
} else {
self.timeInterval = self.timeInterval == 0 ? defaultInterval : self.timeInterval; // 是否自定义，否则用默认值
[self performSelector:@selector(resetState) withObject:nil afterDelay:defaultInterval];
}
}
// 此处 methodA 和 methodB方法IMP互换了，实际上执行 sendAction；所以不会死循环
self.isIgnoreEvent = YES;
[self mo_sendAction:action to:target forEvent:event]; // 执行系统的原有方法
}
// 还有些属性，没添加，详情见Demo- `UILabel`的`Category`中拦截初始化方法，并设置font
// UILabel+Swizzling.m
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self methodSwizzlingWithOriginalSelector:@selector(init) bySwizzledSelector:@selector(mo_Init)];
[self methodSwizzlingWithOriginalSelector:@selector(initWithFrame:) bySwizzledSelector:@selector(mo_InitWithFrame:)];
[self methodSwizzlingWithOriginalSelector:@selector(awakeFromNib) bySwizzledSelector:@selector(mo_AwakeFromNib)];
});
}
- (instancetype)mo_Init {
id __self = [self mo_Init];
UIFont *font = [UIFont fontWithName:@"Zapfino" size:self.font.pointSize];
if (font) {
self.font = font;
}
return __self;
}
- (instancetype)mo_InitWithFrame:(CGRect)rect {
id __self = [self mo_InitWithFrame:rect];
UIFont *font = [UIFont fontWithName:@"Zapfino" size:self.font.pointSize];
if (font) {
self.font = font;
}
return __self;
}
- (void)mo_AwakeFromNib {
[self mo_AwakeFromNib];
UIFont *font = [UIFont fontWithName:@"Zapfino" size:self.font.pointSize];
if (font) {
self.font = font;
}
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原始发表：2020-02-25，如有侵权请联系 cloudcommunity@tencent.com 删除
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