Blog by Frank

UIKit Intro in Objective-C & Swift

Everything about UIKit in Objective-C & Swift when I was coding.

hws - UIKit Example Code

QuickStart

Debug Tools

Flex

#if os(iOS)
import FLEX
#endif

#if DEBUG
//import FLEX
#endif

#if DEBUG
ToolbarItemGroup {
    Button("Flex") {
        FLEXManager.shared.showExplorer()
    }
//                darkModeButton
}
#endif

Components QuickStart

graph LR

Button --> UIButton --> f2[Trigger action]

Text --> UILabel --> f1[Display text]
Text --> UITextField --> f3[Enter Signle Line Text]
Text --> UITextView --> f4[Enter Multiple Line Text]

Image --> UIImageView --> f5[Display Image]

Scroll --> UIScrollView --> UITextView

Gesture --> UIGestureRecognizer --> UITapGesture

Effect --> UIBlurEffect

UITableView
UICollectioView
UIStackView

Delegate，类扩展

@interface ViewController ()<UITextFieldDelegate, UITextViewDelegate>

@end

() 表示这是一个匿名分类（也叫类扩展或匿名类别），可以在其中添加实例变量和方法。<UICollectionViewDelegate, UICollectionViewDataSource,UICollectionViewDelegateFlowLayout> 表示这个类实现了 UICollectionViewDelegate、UICollectionViewDataSource 和 UICollectionViewDelegateFlowLayout 这三个协议。在 Objective-C 中，需要在类的声明中明确列出所实现的协议，这有助于编译器检查类是否实现了协议中规定的所有方法。

@interface TestingUICollectionViewCell ()<UICollectionViewDelegate, UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>
@end

class TestingUICollectionViewCell: UICollectionViewCell, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    // class implementation goes here
}

Button

// in file ViewController.m
- (void)viewDidLoad {
    [super viewDidLoad];

    UIButton *button = [UIButton buttonWithType:
									UIButtonTypeSystem];
    [button setTitle:@"Press Me" forState:UIControlStateNormal];
    [button sizeToFit];

	// Set a new (x,y) point for the button's center
    button.center = CGPointMake(320 / 2, 60);

	// Add an action in current code file (i.e. target)
    [button addTarget:self 
			action:@selector(buttonPressed:）
			forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:button];
} 

- (void)buttonPressed:(UIButton *)button {
     NSLog(@"Button Pressed");
}

// Another Button
- (void)viewDidLoad {
    [super viewDidLoad];

    UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(100, 100, 200, 200)];
    [button setTitle:@"hello" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}

- (void)buttonPressed {
    NSLog(@"Hello world");
}

UILabel & UITextField & UITextView

//
//  ViewController.m
//  DouyinObjc
//
//  Created by Chu Yong on 5/13/23.
//

#import "ViewController.h"

@interface ViewController ()<UITextFieldDelegate, UITextViewDelegate>

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor redColor];
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
    label.text = @"Hello World";
    label.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:label];
    
    // TextFields
    UITextField *textfield = [[UITextField alloc] initWithFrame:CGRectMake(0, 200, UIScreen.mainScreen.bounds.size.width, 200)];
    textfield.text = @"Hello";
    textfield.placeholder = @"Enter something";
    textfield.delegate = self;
    [self.view addSubview:textfield];
    
    // TextView
    UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(0, 400, UIScreen.mainScreen.bounds.size.width, 200)];
    textView.text = @"Hello";
    textView.backgroundColor = [UIColor yellowColor];
    textView.delegate = self;
    [self.view addSubview:textView];
}

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    if ([text isEqualToString:@"\n"]) {
        [textView resignFirstResponder];
    }
    return YES;
}

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    [textField resignFirstResponder];
    return YES;
}

- (void)textFieldDidBeginEditing:(UITextField *)textField {
    NSLog(@"%@", textField.text);
}
@end

Masonry Constraint for UILabel

layoutMargins

Remove UILabel padding

//        _contentLabel.directionalLayoutMargins = NSDirectionalEdgeInsetsMake(0, 0, 0, 0);
//        _contentLabel.layoutMargins = UIEdgeInsetsMake(0, 0, 0, 0);

directionalLayoutMargins

directionalLayoutMargins 是UIView的一个属性，用于指定在考虑当前语言方向时布局视图内容时使用的默认间距。这个属性的类型是NSDirectionalEdgeInsets，该结构具有leading，top，trailing和bottom四个方向的边距。

leading和trailing的概念是相对的，并且依赖于用户界面的当前语言环境。在从左到右的语言环境中，leading边距位于左边，trailing边距位于右边；而在从右到左的语言环境中，这两者会互换位置。

使用directionalLayoutMargins可以帮助您在支持右到左语言环境的应用中实现适应性布局。以下是一个使用directionalLayoutMargins的例子：

objc Copy code // 创建一个新的视图 UIView *newView = [[UIView alloc] init];

// 设置视图的方向性边距 newView.directionalLayoutMargins = NSDirectionalEdgeInsetsMake(10, 20, 30, 40);

// 通过代码或者自动布局约束来进行布局 // 当在一个从右到左的语言环境中查看这个视图时，leading边距会位于右边，trailing边距会位于左边 当然，需要注意的是，directionalLayoutMargins并不会直接改变视图的内容布局。要使directionalLayoutMargins生效，还需要结合使用AutoLayout约束，特别是在创建约束时使用NSLayoutAnchor的leadingAnchor和trailingAnchor，而不是leftAnchor和rightAnchor。

UIImage

// UIImage
UIImage *image = [UIImage systemImageNamed:@"plus"];
UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
imageView.frame = CGRectMake(50, 50, 20, 200);
imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.layer.borderWidth = 1.0;
imageView.layer.borderColor = [UIColor yellowColor].CGColor;
[self.view addSubview:imageView];

Aspect Fit

UITableView & UICollectionView

【抖音OC实战教程-View讲解03（05）】

UITableView 和 UICollectionView 是 iOS 中常用的两种列表控件。

UITableView 是一个列表控件，可以用来展示单行或多行数据。它是基于 Model-View-Controller 设计模式的。UITableView 中的每个 cell 都可以由一个 UITableViewCell 类型的实例表示，而这个实例通常包含了一些 UI 元素和一些用来展示数据的控件。UITableView 中可以设置 section 来分组显示数据。

UICollectionView 是一个强大的集合控件，可以用来展示多行、多列的数据。它也是基于 Model-View-Controller 设计模式的。与 UITableView 不同，UICollectionView 的布局方式更加灵活，可以通过设置 layout 来控制每个 cell 的大小、位置、对齐方式等等。与 UITableView 相似，UICollectionView 也可以使用 section 来分组显示数据，而且它还支持一些特殊的布局方式，如流式布局等。

总的来说，UITableView 适用于简单的列表展示，而UICollectionView 则更加适用于展示多样化、样式复杂的数据，同时它的布局方式更加灵活。

//
//  ViewController.m
//  DouyinObjc
//
//  Created by Chu Yong on 5/13/23.
//

#import "ViewController.h"

@interface ViewController ()<UICollectionViewDelegate, UICollectionViewDataSource>
@property (nonatomic, strong) NSMutableArray <NSArray *>*sections;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // UICollectionView
    self.sections = [NSMutableArray array];
    [self.sections addObject:@[@"123"]];
    [self.sections addObject:@[@"3", @"4"]];
    [self.sections addObject:@[@"3", @"4", @"3", @"4"]];

    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    
    layout.itemSize = CGSizeMake(100, 200);
    layout.minimumLineSpacing = 20;
    layout.sectionInset = UIEdgeInsetsMake(0, 0, 50, 0);
    [collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cell"];
    
    collectionView.delegate = self;
    collectionView.dataSource = self;
    
    [self.view addSubview:collectionView];
}

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return self.sections.count;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return self.sections[section].count;
}

- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
    
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 50, 50)];
    label.text = self.sections[indexPath.section][indexPath.row];
    [cell addSubview:label];
    
    cell.backgroundColor = [UIColor redColor];
    return cell;
}
@end

Header footer for UITableView

iOS-UITableViewCell自适应高度最优雅的方法

隐藏分割线

iOS 中隐藏UITableView最后一条分隔线

// 分割线
// _tableView.separatorStyle = UITableViewCellSeparatorStyleSingleLine;
if (indexPath.row == _menuStringArray.count-1) {
    menuCell.separatorInset = UIEdgeInsetsMake(0, self.bounds.size.width, 0, 0);
} else{
    menuCell.separatorInset = UIEdgeInsetsMake(0, FTDefaultMenuTextMargin, 0, 10+FTDefaultMenuTextMargin);
}

Grouped UITableview remove outer separator line

Grouped UITableview remove outer separator line

// Get the width of tableview
// https://stackoverflow.com/questions/29006311/grouped-uitableview-remove-outer-separator-line
for (UIView *subview in cell.subviews) {
    if (subview != cell.contentView && subview.frame.size.width == cell.width) {
        [subview removeFromSuperview];
    }
}

Protocol & UICollectionView

// ViewController.h
// <> Means Controller conform delegate inside <>
@interface ViewController : UIViewController <UICollectionViewDelegate, UICollectionViewDataSource>
@end

@interface ViewController ()
@property (nonatomic, strong) UICollectionView *collectionView;
@end

collectionView:cellForItemAtIndexPath:

Asks your data source object for the cell that corresponds to the specified item in the collection view.

@implementation ViewController
- (void)viewDidLoad {
	[super viewDidLoad];
	[self loadCollectioView];
}

- (void)loadCollectioView {
    // Layout Init
    // let layout = UICollectionViewFlowLayout()
    UICollectionViewFlowLayout *flowlayout = [[UICollectionViewFlowLayout alloc] init];
    
    // self.collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
    _collectionView = [[UICollectionView alloc]initWithFrame:self.view.frame collectionViewLayout:flowlayout];
    
    // Cell Size
    flowlayout.itemSize = CGSizeMake(280, 280);
    
    // head Size
    flowlayout.headerReferenceSize = CGSizeMake(self.view.frame.size.width, 40);
    
    // Cell vertical spacing
    flowlayout.minimumLineSpacing = 10;
    
    // Cell horizontal spacing
    flowlayout.minimumInteritemSpacing = 20;
    
    // Cell to container edge
    flowlayout.sectionInset = UIEdgeInsetsMake(20, 20, 20, 20); // Up left down right
    
    // collectionView init
    
    // Register Cell !! IMPORTANT
    // collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cell"];
    
    // Set delegate
    // collectionView.dataSource = self
    // collectionView.delegate = self
    _collectionView.dataSource = self;
    _collectionView.delegate = self;
    
    // Background color
    _collectionView.backgroundColor = [UIColor greenColor];
    
    // Felxible Width & Height
    _collectionView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    
    // Add View
    [self.view addSubview:_collectionView];
    
    // Size settings
    [_collectionView setFrame:self.view.frame];
}

- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    
    // Cell Reuse, identifier is same as the registration(@"cell")
    // let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];

    // Optional
    if (!cell) {
        cell = [[UICollectionViewCell alloc] init];
//        [cell.contentView setBackgroundColor:[UIColor systemBlueColor]];
    }
    // cell.contentView.backgroundColor = .systemBlue
    [cell.contentView setBackgroundColor:[UIColor systemBlueColor]];
    return cell;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return 120;
}
@end

import UIKit

class ViewController: UIViewController {
    
    var collectionView: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.view.backgroundColor = .green
        
        let flowLayout = UICollectionViewFlowLayout()
        self.collectionView = UICollectionView(frame: self.view.safeAreaLayoutGuide.layoutFrame, collectionViewLayout: flowLayout)
        
        flowLayout.scrollDirection = .horizontal
        flowLayout.itemSize = CGSizeMake(180, 180)
        
        collectionView.delegate = self
        collectionView.dataSource = self
        
        collectionView.register(ExampleCell.self, forCellWithReuseIdentifier: String(describing: type(of: ExampleCell.self)))
        
        self.view.addSubview(collectionView)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

extension ViewController: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: String(describing: type(of: ExampleCell.self)), for: indexPath) as! ExampleCell
        cell.titleLabel.text = String(indexPath.row)
        return cell
    }
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        1
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        10
    }
}

extension ViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print("Selected item at index: \(indexPath.row)")
    }
}

class ExampleCell: UICollectionViewCell {
    let titleLabel = UILabel()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        self.initUI()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func initUI() {
        self.backgroundColor = .red
        
        // Text for index
        titleLabel.frame = CGRect(x: 50, y: 50, width: 50, height: 20)
        self.addSubview(titleLabel)
    }
}

No Storyboard

guard let windowScene = (scene as? UIWindowScene) else { return }
window = UIWindow(frame: windowScene.coordinateSpace.bounds)
window?.windowScene = windowScene
window?.rootViewController = ViewController()
window?.makeKeyAndVisible()

这段代码是使用 Objective-C 编写的。在 Objective-C 中，我们需要显式地进行类型转换，并使用方括号表示方法调用和消息发送的语法。同样，也需要手动创建 UIWindow 对象，并将其设置为应用程序的主窗口。注意，ViewController 是你应用程序中的视图控制器类的名称，你需要根据实际情况进行替换。

UIWindowScene *windowScene = (UIWindowScene *)scene;
if (![windowScene isKindOfClass:[UIWindowScene class]]) {
    return;
}
self.window = [[UIWindow alloc] initWithFrame:windowScene.coordinateSpace.bounds];
self.window.windowScene = windowScene;
self.window.rootViewController = [[ViewController alloc] init];
[self.window makeKeyAndVisible];

Loading Method of AppDelegate, SceneDelegate and Controller AppDelegate、SceneDelegate、控制器的加载方式

iOS13 之前，AppDelegate的职责是：全权处理App生命周期和UI生命周期

Before iOS13, the AppDelegate is responsible for handling the entire App lifecycle and the UI lifecycle.

iOS 13 之后，AppDelegate的职责是：处理App生命周期和SceneDelegate 生命周期

After iOS 13, the AppDelegate is responsible for handling the App lifecycle and the SceneDelegate lifecycle.

StartUp Process 启动过程

main函数 -> 自动释放池 -> UIApplicationMain（永不返回，保证程序不会被销毁）-> 创建应用程序对象UIApplication ->创建应用程序的代理对象AppDelegate -> IOS13之前，将AppDelegate的window实例化，设置为keyWindow主窗口 -> 加载配置文件指定的storyboard

main function -> autorelease pool -> UIApplicationMain (never returns, to ensure that the program will not be destroyed) -> create the application object UIApplication -> create the application delegate object AppDelegate -> IOS13 before, instantiate the AppDelegate’s window, set it as the keyWindow main window -> load the storyboard specified in the configuration file

UIKit UIViewController Lifecycle

graph TD
load --> loadView --> viewDidLoad --> viewWillAppear --> viewWillLayoutSubviews --> viewDidLayoutSubviews --> viewDidAppear
viewDidAppear --> viewWillDisappear --> viewDidDisappear

//
//  ViewController.m
//  DouyinObjc
//
//  Created by Chu Yong on 5/13/23.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

+ (void)load {
    [super load];
    NSLog(@"1");
}

- (void)loadView {
    [super loadView];
    NSLog(@"2");
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    NSLog(@"3");
    
    self.view.backgroundColor = [UIColor redColor];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"4");
}

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    NSLog(@"5");
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    NSLog(@"6");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"7");
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"8");
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"9");
}

- (void)dealloc {
    NSLog(@"10");
}

@end

MVC

graph LR
UIViewController --> Model
UIViewController --> UIView
Model --X--> UIView

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor redColor];
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
    label.text = @"Hello World";
    [self.view addSubview:label];
}

Target for Project in Xcode

<!-- Info.plist -->
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>UIApplicationSceneManifest</key>
	<dict>
		<key>UIApplicationSupportsMultipleScenes</key>
		<false/>
		<key>UISceneConfigurations</key>
		<dict>
			<key>UIWindowSceneSessionRoleApplication</key>
			<array>
				<dict>
					<key>UISceneConfigurationName</key>
					<string>Default Configuration</string>
					<key>UISceneDelegateClassName</key>
					<string>SceneDelegate</string>
				</dict>
			</array>
		</dict>
	</dict>
</dict>
</plist>

<key>Storyboard Name</key>

Delegate

SwiftUI In UIKit(Objective-C)

import SwiftUI
struct MainViewInterface: View {
     var body: some View {
          Text("Hello, World!")
   }
}

@objc
class MainView: NSObject {
    @objc func makeMainView() -> UIViewController {
        return UIHostingController(rootView:  MainViewInterface())
    }
}

// #import "<projectName>-Swift.h"
// Lookup in Targets - Build Settings - Search for Swift - Objective-C Generated Interface Header Name
#import "testSwift-Swift.h" 

@implementation ViewController

- (void)viewDidLoad {
	[super viewDidLoad];

	UIViewController *vc = [[MainView new] makeMainView];
	vc.view.frame = CGRectMake(100, 400, 200, 100);
	[self.view addSubview:vc.view];
}

@end

Display SwiftUI views from Objective-C codebase

@objc class HelloWorldViewFactory: NSObject {
    
    @objc static func create(text: String) -> UIViewController {
        let helloWorldView = HelloWorldView(text: text)
        let hostingController = UIHostingController(rootView: helloWorldView)
        
        return hostingController
    }
}

UIViewController *vc = [HelloWorldViewFactory createWithText:@"Hello from Obj-C!"];
[self presentViewController:vc animated:YES completion:nil];

Presenting SwiftUI Views from ObjectiveC

import Foundation
import SwiftUI

class SwiftUIViewFactory: NSObject {
  @objc static func makeSwiftUIView(dismissHandler: @escaping (() -> Void)) -> UIViewController {
    return UIHostingController(rootView: SwiftUIView(dismiss: dismissHandler))
  }
}

- (IBAction)showSwiftUIView:(id)sender {
  UIViewController *vc = [SwiftUIViewFactory makeSwiftUIViewWithDismissHandler:^{
    [[self presentedViewController] dismissViewControllerAnimated:YES completion:nil];
  }];
  [self presentViewController:vc animated:YES completion:nil];
}

Full Code

UIButton *btn = [UIButton buttonWithType:UIButtonTypeSystem];
[btn setTitle:@"HI" forState:UIControlStateNormal];
[btn addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
btn.frame = CGRectMake(100, 100, 200, 50);
[self.view addSubview:btn];

- (void)buttonClicked {
    UIViewController* vc = [SwiftUIViewFactory makeSwiftUIViewWithDismissHandler:^{
        [[self presentedViewController] dismissViewControllerAnimated:YES completion:nil];
    }];
    [self presentViewController:vc animated:YES completion:nil];
}

class SwiftUIViewFactory: NSObject {
    @objc static func makeSwiftUIView(dismissHandler: @escaping (() -> Void)) -> UIViewController {
        return UIHostingController(rootView: ContentView(dismiss: dismissHandler))
    }
}

Presenting SwiftUI Views from ObjectiveC

Display SwiftUI views from Objective-C codebase

@objc class HelloWorldViewFactory: NSObject {
    
    @objc static func create(text: String) -> UIViewController {
        let helloWorldView = HelloWorldView(text: text)
        let hostingController = UIHostingController(rootView: helloWorldView)
        
        return hostingController
    }
}

UIViewController *vc = [HelloWorldViewFactory createWithText:@"Hello from Obj-C!"];
[self presentViewController:vc animated:YES completion:nil];

Presenting SwiftUI Views from ObjectiveC

import Foundation
import SwiftUI

class SwiftUIViewFactory: NSObject {
  @objc static func makeSwiftUIView(dismissHandler: @escaping (() -> Void)) -> UIViewController {
    return UIHostingController(rootView: SwiftUIView(dismiss: dismissHandler))
  }
}

- (IBAction)showSwiftUIView:(id)sender {
  UIViewController *vc = [SwiftUIViewFactory makeSwiftUIViewWithDismissHandler:^{
    [[self presentedViewController] dismissViewControllerAnimated:YES completion:nil];
  }];
  [self presentViewController:vc animated:YES completion:nil];
}

Full Code

UIButton *btn = [UIButton buttonWithType:UIButtonTypeSystem];
[btn setTitle:@"HI" forState:UIControlStateNormal];
[btn addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
btn.frame = CGRectMake(100, 100, 200, 50);
[self.view addSubview:btn];

- (void)buttonClicked {
    UIViewController* vc = [SwiftUIViewFactory makeSwiftUIViewWithDismissHandler:^{
        [[self presentedViewController] dismissViewControllerAnimated:YES completion:nil];
    }];
    [self presentViewController:vc animated:YES completion:nil];
}

class SwiftUIViewFactory: NSObject {
    @objc static func makeSwiftUIView(dismissHandler: @escaping (() -> Void)) -> UIViewController {
        return UIHostingController(rootView: ContentView(dismiss: dismissHandler))
    }
}

Presenting SwiftUI Views from ObjectiveC

Lazy Instantiation

See more in objc-snippet

Border

kingfisher - onevcat on twitter

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@property (weak, nonatomic) IBOutlet UIImageView *secondImgView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.imageView.layer.cornerRadius = self.imageView.frame.size.width / 2;
    self.imageView.layer.masksToBounds = true;
    self.imageView.layer.borderWidth = 2.0;
    self.imageView.layer.borderColor = [UIColor whiteColor].CGColor;
    self.secondImgView.layer.cornerRadius = self.imageView.frame.size.width / 2;
    self.secondImgView.layer.borderWidth = 2.0;
    self.secondImgView.layer.borderColor = [UIColor whiteColor].CGColor;
}

@end

import SwiftUI
struct ContentView: View {
    
    var body: some View {
        HStack {
            ForEach(0..<3, id: \.self) { i in
                Image("icon")
                    .resizable()
                    .frame(width: 100, height: 100)
                    .overlay {
                        Circle()
                            .stroke(.blue, lineWidth: 5)
                    }
                //.cornerRadius(50)
                    .offset(x: CGFloat(-i * 50), y: 0)
            }
        }
    }
    
}

在 SwiftUI 中，视图的修改器是一种声明式方法，用于描述视图的外观和行为。在这种情况下，为了实现与 UIKit 类似的效果，我们需要将边框绘制为一个圆形视图的叠加层。

SwiftUI 与 UIKit 的设计理念有很大差异。在 UIKit 中，我们直接操作视图的层（layer）来实现边框、圆角等效果。而在 SwiftUI 中，我们通过组合和修改视图来实现所需的效果。这种声明式的方式允许 SwiftUI 更好地优化渲染过程，并提供更易读、更易维护的代码。

在上面的 SwiftUI 示例中，我们使用了 overlay 修改器来添加一个描边圆形，从而实现了类似于 UIKit 中的边框效果。虽然这种方法与 UIKit 的操作方式不同，但它非常符合 SwiftUI 的设计原则，并能很好地满足需求。

ResponsiveScaleWidth

#define ResponsiveScaleWidth(length) (((length)/375.0f) * [[UIScreen mainScreen] bounds].size.width)

UIKit Preview

UIKit Preview

import UIKit

class ViewController: UINavigationController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        var text = UILabel(frame: CGRect(x: 20, y: 20, width: 300, height: 300))
        text.text = "UIKit Preview Testing"
        self.view.addSubview(text)
    }
}

#if DEBUG

import SwiftUI

struct ViewControllerRepresentable: UIViewControllerRepresentable {
    typealias UIViewControllerType = ViewController

    func makeUIViewController(context: Context) -> UIViewControllerType {
        ViewController()
    }
    
    func updateUIViewController(_ uiViewController: UIViewControllerType, context: Context) {
        
    }
}

struct ViewController_Previews: PreviewProvider {
    static var previews: some View {
        ViewControllerRepresentable()
    }
}

IBAction

- (IBAction)showSwiftUIView:(id)sender {}

这段代码中的圈表示了方法的返回类型。在 Objective-C 中，方法的返回类型用圆括号括起来，并位于方法名称之前。在这种情况下，(IBAction) 表示该方法返回一个特殊的类型，用于在 Interface Builder 中与用户界面的操作进行关联。

IBAction 是 Objective-C 中特有的关键字，用于表示该方法可以与用户界面的事件进行连接。在 Interface Builder 中，你可以将按钮、手势等与该方法关联起来，以在用户交互时触发该方法的执行。

需要注意的是，IBAction 实际上只是一个宏定义，它将被转换为 void 类型，因此在 Swift 中不需要显示地指定返回类型。在 Swift 中，你可以将方法定义为 @IBAction，并省略返回类型的圆括号。例如，在 Swift 中定义一个类似的方法会更简洁：

@IBAction func showSwiftUIView(_ sender: Any) {
    // 方法的具体实现
}

prepareForSegue

#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}

prepareForSegue:sender: 方法是在使用基于Storyboard的应用程序中进行页面跳转前的准备工作的常用方法。当一个Segue（故事板中的跳转）被触发时，系统会自动调用该方法。

在这个方法中，你可以通过 [segue destinationViewController] 获取目标视图控制器，然后根据需要进行一些准备工作。例如，你可以将数据传递给目标视图控制器，设置目标视图控制器的属性，或执行其他必要的操作。

通常，你可以根据Segue的标识符（identifier）来区分不同的跳转，并根据需要进行相应的准备工作。例如：

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"MySegueIdentifier"]) {
        // 获取目标视图控制器
        MyViewController *destinationViewController = [segue destinationViewController];
        
        // 进行一些准备工作，例如传递数据或设置属性
        destinationViewController.myProperty = myData;
    }
}

通过在 prepareForSegue:sender: 方法中进行准备工作，你可以确保在进行页面跳转之前，目标视图控制器已经准备好接收数据或执行其他操作，以便在跳转后呈现所需的结果。

头文件 import

在 Objective-C 中，#import 是用于导入头文件的预处理指令。它有两种形式：#import <Framework/Module.h> 和 #import “LocalFile.h”。

#import <Framework/Module.h>：这种形式用于导入系统框架或第三方库的头文件。<Framework/Module.h> 是一个相对于系统或第三方库的头文件路径。这种方式通常用于导入公共框架或库的头文件。例如：

#import <UIKit/UIKit.h>
#import <AFNetworking/AFNetworking.h>

#import “LocalFile.h”：这种形式用于导入项目中的自定义头文件或本地文件的头文件。“LocalFile.h” 是一个相对于当前文件的头文件路径。这种方式通常用于导入自定义的类或其他文件的头文件。例如：

#import "MyCustomClass.h"
#import "Constants.h"

总的来说，#import <Framework/Module.h> 用于导入系统框架或第三方库的头文件，而 #import “LocalFile.h” 用于导入项目中的自定义头文件或本地文件的头文件。

需要注意的是，无论使用哪种形式，#import 指令都会在编译时将指定的头文件内容复制到当前文件中，以便在编译过程中能够访问导入的类、函数、常量等内容。

NSString 判空

NSString 判空的最佳方式

How to detect if NSString is null?

if (str.length == 0) {

NSLog(@"str is empty!!!");

}

这句代码可以通吃上面case1、2、3；其实也是好理解的，nil本身也是一个对象，在ios中给nil

发消息是不会崩溃的，只不过没啥反应而已，因此length也是默认的0了；

至于类似于case4的情况，可以先将字符串中的空格"  " Trim掉，然后在进行判断：

OC中的nil、Nil、NULL、NSNull的区别

SF Symbols

How to use default iOS images?

Present an UIAlertController from an UIView

How to present an UIAlertController from an UIView

Observer 观察者

/// 添加系统通知状态的观察者
- (void)addObserverForSystemNotificationStatus {
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(checkNotificationAuthorization)
                                                 name:UIApplicationWillEnterForegroundNotification
                                               object:nil];
}

MJExtension

iOS 关于项目中经常用到的MJExtension函数

iOS MJExtension使用方法指南(Objective-C)

rootViewController

/// 展示 UIAlertController, Workaround
/// - Parameter alertController:
///
/// [Stack Overflow](https://stackoverflow.com/questions/26554894/how-to-present-uialertcontroller-when-not-in-a-view-controller)
+ (id)rootViewController {
    id rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
    if([rootViewController isKindOfClass:[UINavigationController class]])
    {
        rootViewController = ((UINavigationController *)rootViewController).viewControllers.firstObject;
    }
    if([rootViewController isKindOfClass:[UITabBarController class]])
    {
        rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
    }
    return rootViewController;
}

Safe Area

iPhone X Safe Area