小编Yan*_*ivH的帖子

我正在尝试在后台进程中运行一个程序，该程序将注册系统中的每个关闭事件。

通过注册 NSWorkspaceWillPowerOffNotification 来实现此目的，如下所示：

#import <AppKit/AppKit.h>

@interface ShutDownHandler : NSObject <NSApplicationDelegate>

- (void)computerWillShutDownNotification:(NSNotification *)notification;

@end


int main(int argc, char* argv[]) {
    NSNotificationCenter *notCenter;

    notCenter = [[NSWorkspace sharedWorkspace] notificationCenter];

    ShutDownHandler* sdh = [ShutDownHandler new];

    [NSApplication sharedApplication].delegate = sdh;

    [notCenter addObserver:sdh
                  selector:@selector(computerWillShutDownNotification:)
                      name:NSWorkspaceWillPowerOffNotification
                    object:nil];

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [[NSFileManager defaultManager] createFileAtPath:@"./output.txt" contents:nil attributes:nil];
    });

    [[NSRunLoop currentRunLoop] run];

    return 0;
}


@implementation ShutDownHandler

- (void)computerWillShutDownNotification:(NSNotification *)notification {
    NSFileHandle* file = [NSFileHandle fileHandleForUpdatingAtPath: @"./output.txt"];
    [file seekToEndOfFile];

    NSDateFormatter* fmt = [NSDateFormatter new];
    [fmt setDateFormat:@"yyyy-MM-dd …

我试图将属性关联到数组扩展:

private var AssociatedObjectHandle: String = "BlaBLabla"
extension Array {
  var emptyIndex:Int {
    mutating get {
      if let object = objc_getAssociatedObject(self, &AssociatedObjectHandle) {
        return object as! Int
      }
      let index = self.searchEmptyIndex()
      self.emptyIndex = index

      return index
    }
    set {
      let new = (newValue as NSInteger)
      objc_setAssociatedObject(self, &AssociatedObjectHandle, new, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
  }

  func searchEmptyIndex() -> Int {
      if let arr = self as? [Int] {
        return arr.index(of: -1)!
      }

      return -1
  }
}

objc_getAssociatedObject调用总是返回nil !!

任何人都知道为什么？

关于这个,我正在敲打最后一小时...

我是 SwiftUI 的新手，我正在尝试使用.transition，但由于某种原因没有发生转换。

你可以看到下面的代码：

看法

import SwiftUI

struct ContentView: View {
  @ObservedObject var viewModel = ViewModel()
  
  var body: some View {
    if self.viewModel.model.show {
      Text("Showing")
        .padding()
    } else {
      Text("Not Showing")
        .padding()
        .transition(.asymmetric(insertion: .scale, removal: .opacity))
    }
    
    Button {
      self.viewModel.show()
    } label: {
      Text("Tap to change")
    }
  }
}

视图模型

class ViewModel: ObservableObject {
  @Published private(set) var model = Model()
  
  func show() {
    self.model.toggleShow()
  }
}

模型

struct Model {
  var show: Bool = true
  
  mutating func toggleShow() …