iOS runtime 应用场景总结
场景1. 动态分类关联属性
场景2. hook/Method Swizzling
场景3. 遍历类属性方法，映射解析以及字典与模型的转换, 例如YYModel
场景4. 修改isa指针（研究中）
场景5. 实现消息转发机制的补救
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一般选择第二步 forwardingTargetForSelector 来做崩溃防护，原因如下：
resolveInstanceMethod 需要在类的本身上动态添加它本身不存在的方法；
forwardInvocation可以通过NSInvocation的形式将消息转发给多个对象，但是其开销较大，需要创建新的NSInvocation对象，并且forwardInvocation的函数经常被使用者调用，来做多层消息转发选择机制，不适合多次重写；
forwardingTargetForSelector可以将消息转发给一个对象，开销较小，可以NSObject的该方法重写，做以下几步的处理：
1). 动态创建一个桩类
2). 动态为桩类添加对应的Selector，用一个通用的返回0的函数来实现该SEL的IMP
3). 将消息直接转发到这个桩类对象上。
场景6. 实现 NSCoding 的自动归档和解档（暂不支持嵌套，可用于详情模型的本地存储）
- (void)encodeWithCoder:(NSCoder *)aCoder {
// 一个临时数据, 用来记录一个类成员变量的个数
unsigned int ivarCount = 0;
// 获取一个类所有的成员变量
Ivar *ivars = class_copyIvarList(self.class, &ivarCount);
// 变量成员变量列表
for (int i = 0; i < ivarCount; i ++) {
// 获取单个成员变量
Ivar ivar = ivars[i];
// 获取成员变量的名字并将其转换为 OC 字符串
NSString *ivarName = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 获取该成员变量对应的值
id value = [self valueForKey:ivarName];
// 归档, 就是把对象 key-value 对 encode
[aCoder encodeObject:value forKey:ivarName];
}
// 释放 ivars
free(ivars);
}
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
// 因为没有 superClass 了
self = [self init];
if (self != nil) {
unsigned int ivarCount = 0;
Ivar *ivars = class_copyIvarList(self.class, &ivarCount);
for (int i = 0; i < ivarCount; i ++) {
Ivar ivar = ivars[i];
NSString *ivarName = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 解档, 就是把 key-value 对 decode
id value = [aDecoder decodeObjectForKey:ivarName];
// 赋值
[self setValue:value forKey:ivarName];
}
free(ivars);
}
return self;
}
场景7.分类重写 kvc 方法，防崩溃
-(void)setValue:(id)value forUndefinedKey:(NSString *)key{
NSLog(@"setValue: forUndefinedKey:, 动态创建Key: %@",key);
objc_setAssociatedObject(self, CFBridgingRetain(key), value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
-(nullable id)valueForUndefinedKey:(NSString *)key{
NSLog(@"valueForUndefinedKey:, 获取未知键 %@ 的值", key);
// return nil;
return objc_getAssociatedObject(self, CFBridgingRetain(key));
}
-(void)setNilValueForKey:(NSString *)key{
NSLog(@"Invoke setNilValueForKey:, 不能给非指针对象(如NSInteger)赋值 nil");
return;//给一个非指针对象(如NSInteger)赋值 nil, 直接忽略
}
场景 8：获取类的成员变量，属性，方法，协议
- (void)enumerateIvars:(void(^)(Ivar v, NSString *name, _Nullable id value))block{
unsigned int count;
Ivar *ivars = class_copyIvarList(self.class, &count);
for(NSInteger i = 0; i < count; i++){
Ivar ivar = ivars[i];
NSString *ivarName = [NSString stringWithUTF8String:ivar_getName(ivar)];
id value = [self valueForKey:ivarName];//kvc读值
if (block) {
block(ivar, ivarName, value);
}
}
free(ivars);
}
- (void)enumeratePropertys:(void(^)(objc_property_t property, NSString *name, _Nullable id value))block{
unsigned int count = 0;
objc_property_t *properties = class_copyPropertyList(self.class, &count);
for (int i = 0; i < count; i++) {
objc_property_t property_t = properties[i];
const char *name = property_getName(property_t);
NSString *propertyName = [NSString stringWithUTF8String:name];
id value = [self valueForKey:propertyName];
if (block) {
block(property_t, propertyName, value);
}
}
free(properties);
}
- (void)enumerateMethods:(void(^)(Method method, NSString *name))block{
unsigned int count = 0;
Method *methodList = class_copyMethodList(self.class, &count);
for (unsigned int i = 0; i < count; i++) {
Method method = methodList[i];
SEL mthodName = method_getName(method);
// NSLog(@"MethodName(%d): %@", i, NSStringFromSelector(mthodName));
if (block) {
block(method, NSStringFromSelector(mthodName));
}
}
free(methodList);
}
- (void)enumerateProtocols:(void(^)(Protocol *proto, NSString *name))block{
unsigned int count = 0;
__unsafe_unretained Protocol **protocolList = class_copyProtocolList(self.class, &count);
for (int i = 0; i < count; i++) {
Protocol *protocal = protocolList[i];
const char *protocolName = protocol_getName(protocal);
// NSLog(@"protocol(%d): %@", i, [NSString stringWithUTF8String:protocolName]);
if (block) {
block(protocal, [NSString stringWithUTF8String:protocolName]);
}
}
free(protocolList);
}
【附】：赋值和取值（没用到过，因为 KVC 更方便）
//获取实例进行赋值操作
Ivar ivar = class_getInstanceVariable([UITextField class], "_placeholderLabel");
object_setIvar(self.textField, ivar, "请输入");
//获取当前类对应特征名称的实例变量,得到该实例变量的数值
Ivar ivar = class_getInstanceVariable([UITextField class], "_placeholderLabel");
id object = object_getIvar(self.textField, ivar);
场景 9. 动态创建/获取 class，selector 等以及视图子元素动态化重构，极大地提高代码复用率
NSClassFromString(@"MyClass");
NSSelectorFromString(@"showShareActionSheet");
场景 10. 动态创建Class
objc_allocateClassPair可以动态创建Class,
objc_registerClassPair进行注册动态创建的Class
修改对象的Class
object_setClass可以修改对象的Class，即修改了isa指针指向的Class对象
场景 11. 动态调整 accessoryView 位置，使其上下居中（默认不居中）
import UIKit
@objc extension UITableViewCell{
override public class func initializeMethod() {
super.initializeMethod();
if self != UITableViewCell.self {
return
}
let onceToken = "Hook_\(NSStringFromClass(classForCoder()))";
DispatchQueue.once(token: onceToken) {
let oriSel = NSSelectorFromString("layoutSubviews")
let repSel = #selector(self.hook_layoutSubviews)
_ = hookInstanceMethod(of: oriSel, with: repSel);
}
}
private func hook_layoutSubviews() {
hook_layoutSubviews()
positionAccessoryView()
}
}
@objc public extension UITableViewCell{
///调整AccessoryView位置(默认垂直居中)
func positionAccessoryView(_ dx: CGFloat = 0, dy: CGFloat = 0) {
var accessory: UIView?
if let accessoryView = self.accessoryView {
accessory = accessoryView
} else if self.accessoryType != .none {
for subview in self.subviews {
if subview != self.textLabel && subview != self.detailTextLabel
&& subview != self.backgroundView && subview != self.selectedBackgroundView
&& subview != self.imageView && subview != self.contentView
&& subview.isKind(of: UIButton.self) {
accessory = subview
break
}
}
}
if accessory != nil {
accessory!.center = CGPoint(x: accessory!.center.x + dx, y: self.bounds.midY + dy)
}
}
}
场景 12. 防止数组越界和字典赋 nil 造成的崩溃（支持语法糖保护）
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_target = [NNForwardingTarget new];;
if (isOpenCashProtector) {
swizzleInstanceMethod(NSClassFromString(@"__NSArrayI"),
@selector(objectAtIndex:), NSSelectorFromString(@"safe_objectAtIndex:"));
swizzleInstanceMethod(NSClassFromString(@"__NSArrayI"),
@selector(objectAtIndexedSubscript:), @selector(safe_objectAtIndexedSubscript:));
swizzleInstanceMethod(NSClassFromString(@"__NSArrayM"),
@selector(objectAtIndex:), NSSelectorFromString(@"safe_objectAtIndex:"));
swizzleInstanceMethod(NSClassFromString(@"__NSArrayM"),
@selector(objectAtIndexedSubscript:), NSSelectorFromString(@"safe_objectAtIndexedSubscript:"));
swizzleInstanceMethod(NSClassFromString(@"__NSArrayM"),
@selector(addObject:), NSSelectorFromString(@"safe_addObject:"));
swizzleInstanceMethod(NSClassFromString(@"__NSArrayM"),
@selector(insertObject:atIndex:), NSSelectorFromString(@"safe_insertObject:atIndex:"));
//NSClassFromString(@"__NSDictionaryM"),objc_getClass("__NSDictionaryM")
swizzleInstanceMethod(NSClassFromString(@"__NSDictionaryM"),
@selector(setObject:forKey:), NSSelectorFromString(@"safe_setObject:forKey:"));
swizzleInstanceMethod(NSClassFromString(@"__NSDictionaryM"),
@selector(setObject:forKeyedSubscript:), @selector(safe_setObject:forKeyedSubscript:));
swizzleInstanceMethod(NSClassFromString(@"__NSDictionaryM"),
@selector(removeObjectForKey:), @selector(safe_removeObjectForKey:));
swizzleInstanceMethod(self.class,
@selector(forwardingTargetForSelector:), @selector(safe_forwardingTargetForSelector:));
}
});
}
@implementation NSArray (CashProtector)
- (id)safe_objectAtIndex:(NSUInteger)index{
if (index >= self.count) {
if (isOpenAssert) NSAssert(index < self.count, @"index越界");
return nil;
}
return [self safe_objectAtIndex:index];
}
- (id)safe_objectAtIndexedSubscript:(NSUInteger)index {
NSUInteger count = self.count;
if (count == 0 || index >= count) {
if (isOpenAssert) NSAssert(index < self.count, @"index越界");
return nil;
}
return [self safe_objectAtIndexedSubscript:index];
}
@end
@implementation NSMutableArray (CashProtector)
- (id)safe_objectAtIndex:(NSUInteger)index{
if (index >= self.count) {
// DDLog(@"index越界");
if (isOpenAssert) NSAssert(index < self.count, @"index越界");
return nil;
}
return [self safe_objectAtIndex:index];
}
- (id)safe_objectAtIndexedSubscript:(NSUInteger)index {
NSUInteger count = self.count;
if (count == 0 || index >= count) {
return nil;
}
return [self safe_objectAtIndexedSubscript:index];
}
- (void)safe_addObject:(id)anObject{
if(!anObject){
if (isOpenAssert) NSAssert(anObject, @"anObject不能为nil");
return ;
}
[self safe_addObject:anObject];
}
- (void)safe_insertObject:(id)anObject atIndex:(NSUInteger)index{
if(!anObject){
if (isOpenAssert) NSAssert(anObject, @"anObject不能为nil");
return ;
}
[self safe_insertObject:anObject atIndex:index];
}
@end
@implementation NSMutableDictionary (CashProtector)
- (void)safe_setObject:(id)anObject forKey:(id <NSCopying>)aKey{
if (isOpenAssert) NSAssert(anObject && aKey, @"anObject和aKey不能为nil");
if (anObject && aKey) {
[self safe_setObject:anObject forKey:aKey];
}
}
- (void)safe_setObject:(id)anObject forKeyedSubscript:(id <NSCopying>)aKey {
// if (isOpenAssert) NSAssert(anObject && aKey, @"anObject和aKey不能为nil");
if (anObject && aKey) {
[self safe_setObject:anObject forKeyedSubscript:aKey];
}
}
- (void)safe_removeObjectForKey:(id <NSCopying>)aKey {
if (isOpenAssert) NSAssert(aKey, @"aKey不能为nil");
if (aKey) {
[self safe_removeObjectForKey:aKey];
}
}
@end
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