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终端退出 App：osascript -e 'quit app "Xcode"'

ChenYilong/iOSInterviewQuestions: iOS interview questions;iOS 面试题集锦（附答案）

公众号​

百度 APP 技术：百度 APP iOS 端内存优化-原理篇

字节跳动技术团队：iOS 高刷屏监控 + 优化：从理论到实践全面解析

阿里巴巴终端技术：夸克 iOS Top1 JSC 崩溃攻克之旅

腾讯音乐技术团队：iOS Crash 防护你看这个就够了-上篇

微信客户端技术团队：iOS 微信全文搜索技术优化

设备信息​

List of iOS and iPadOS devices - Wikipedia

iOS Resolution // Display proerties of every iPhone, iPad and iPod touch Apple ever made

Apple iPhone 13 - Full phone specifications

iPhone RAM Size Comparison Chart: All The Models Listed

How Much RAM Is in the iPhone 13? Why Apple Doesn't Give Specs - The Mac Security Blog

List of Apple's mobile device codes types and their matching product names

Lookin - 免费好用的 iOS UI 调试软件

私有库及私有 API：iOS-Runtime-Headers

iPhone 设备内存信息​

内存设备
6GBiPhone 13 Pro Max, iPhone 13 Pro, iPhone 12 Pro Max, iPhone 12 Pro
4GBiPhone SE (2022), iPhone 13, iPhone 13 mini, iPhone 12, iPhone 12 mini, iPhone 11, iPhone 11 Pro, iPhone 11 Pro Max
3GBiPhone SE (2nd Gen), iPhone XS, iPhone XS Max, iPhone XR, iPhone X, iPhone 8 Plus, iPhone 7 Plus
2GBiPhone 8, iPhone 7, iPhone SE, iPhone 6s Plus, iPhone 6s
1GBiPhone 6 Plus, iPhone 6, iPhone 5s, iPhone 5C, iPhone 5
512MBiPhone 4S, iPhone 4
256MBiPhone 3GS
128MBiPhone, iPhone 3G

IPA​

APNG​

Animated PNG (APNG) Maker

Online APNG Assembler

APNG Software

iOS 10 及以上允许使用无线数据​

解决方案

动态加载私有库，并调用私有 API 实现。

#import <dlfcn.h>

void * FTServicesHandle = dlopen("/System/Library/PrivateFrameworks/FTServices.framework/FTServices", RTLD_LAZY);
Class NetworkSupport = NSClassFromString(@"FTNetworkSupport");
id networkSupport = [NetworkSupport performSelector:NSSelectorFromString(@"sharedInstance")];
[networkSupport performSelector:NSSelectorFromString(@"dataActiveAndReachable")];
dlclose(FTServicesHandle);

仅供参考！目前不建议在 App Store 正式版中使用，企业 app 中可以随意使用。现在苹果禁止在使用 dlopen(), dlsym(), respondsToSelector:, performSelector:, method_exchangeImplementations() 时传入动态生成的参数，这通过静态分析是能够被检查出来的。苹果会检查引用了这些符号的那部分汇编代码，判断传入的参数是否是静态编译的。

网络​

可供调试的接口：http://requestbin.net/，https://httpbin.org/get，https://httpbin.org/post

模拟器用的网络调节器：先下载，copying the .prefPane file to: /Library/PreferencePanes

Charles HTTPS 抓包检查：

  1. 电脑上的证书是否已安装好（Help - SSL Proxying - Install Charles Root Certificate），Keychain Access 中是否已信任。
  2. 手机上连上代理，访问 <chls.pro/ssl> 下载证书，然后有两个地方要启用：在 General - Profile 中启用，在 General - About - Certificate Trust Settings 中启用。

配置 SSL 代理：

img

Charles 在线破解工具

可视化调试：一款 POSTMAN 的替代品，Chrome 插件 Talend API Tester

copy, mutableCopy​

NSObject 有两个方法，

  • copy 调用了 NSCopying 协议的 copyWithZone: 方法；
  • mutableCopy 调用了 NSMutableCopying 协议的 mutableCopyWithZone: 方法。

当 NSMutableArray 声明为 copy 的属性时：

@property(nonatomic, copy) NSMutableArray* mutableArray;

它的背后实现是：

-(void)setMutableArray:(NSMutableArray *)mutableArray {
    _mutableArray = [mutableArray copy];
}

因此，mutableArray 实际得到的是一个 NSArray 对象，如果对它调用 insertObject:atIndex: 等方法，就会崩溃。

当修饰可变类型的属性时，如 NSMutableArray、NSMutableDictionary、NSMutableString，用 strong；

当修饰不可变类型的属性时，如 NSArray、NSDictionary、NSString，用 copy（这些类型在属性赋值时，右边的值有可能是它们的可变版本。这样当可变版本对象进行增删改的时候，属性也会相应被修改，所以它们都应该用 copy）。

Sending copy to a mutable class returns an immutable copy of the object. But, sending copy to an immutable counterpart is equivalent to sending it a retain message.

@interface DemoClass : NSObject
@property (nonatomic, copy) NSString *strCopy;
@property (nonatomic, strong) NSString *strStrong;
@end

DemoClass *demo = [[DemoClass alloc] init];
NSMutableString *hello = [NSMutableString stringWithFormat:@"Hello"];
demo.strCopy = hello;
demo.strStrong = hello;
[hello appendString:@" world!"];

NSLog​

The simple truth is that NSLog is just plain slow. Why?

NSLog does 2 things:

  1. It writes log messages to the Apple System Logging (asl) facility. This allows log messages to show up in Console.app.
  2. It also checks to see if the application's stderr stream is going to a terminal (such as when the application is being run via Xcode). If so it writes the log message to stderr (so that it shows up in the Xcode console).

Writing to STDERR doesn't sound difficult. But what about asl? 第二点听起来不难，但第一点呢？

To send a log message to the ASL facility, you basically open a client connection to the ASL daemon and send the message. BUT - each thread must use a separate client connection. So, to be thread safe, every time NSLog is called it opens a new asl client connection, sends the message, and then closes the connection.

The lumberjack framework avoids much of the cost by creating a single re-usable asl client connection for its background logging thread.

URLSession 内存关系​

在开发过程中遇到一个疑惑，为什么函数内的局部变量 urlSession 和 dataTask 不会被释放，用了一个 demo 来验证。

class ViewController: UIViewController {
    weak var weakObj: NSObject?
    weak var weakTask: URLSessionDataTask?
    weak var weakURLSession: URLSession?

    override func viewDidLoad() {
        super.viewDidLoad()

        // 对照组
        let obj = NSObject()
        self.weakObj = obj
        // viewDidLoad() 执行完后 obj 被释放

        let urlSession = URLSession(configuration: .default)
        self.weakURLSession = urlSession
        let url = URL(string: "https://www.baidu.com/")!
        let task = urlSession.dataTask(with: url) { (data, response, error) in
            print("response")
        }
        self.weakTask = task
        task.resume()

        // 等待 task 执行完后，urlSession、task 才会释放，不调用这个方法，会内存泄漏
        urlSession.finishTasksAndInvalidate()
    }
}

内存图：

img-80

编译报错​

clang: error: linker command failed with exit code 1 (use -v to see invocation)
1 error generated.
2 errors generated.