public delegate void SetTextHandler(string result)

`public delegate void SetTextHandler(string result)` 是 C# 中的一种委托声明，用于创建一个可以处理字符串参数的方法的引用类型。在这里，`SetTextHandler` 是委托名称，代表了一个函数签名，它接受一个 `string` 类型的参数并返回 `void`（无值）。通过这种方式，你可以将这个委托作为事件处理器，当某个特定的操作完成（比如从数据库获取数据或网络请求响应），并且结果已准备好时，可以调用指定的 `SetTextHandler` 函数并将结果传递给它。

例如，在Windows Forms中，你可能会有一个事件，当文本加载完成后，会触发这个委托，将结果显示到界面上：

public event SetTextHandler TextLoaded;

private void LoadTextFromDatabase(string sqlQuery)
{
   // ...执行数据库操作...
   string result = "查询结果";
   if (TextLoaded != null)
       TextLoaded(result);
}

当你订阅这个事件时，你可以提供自定义的处理代码：

LoadTextFromDatabase(...); // 触发事件
OnTextLoaded += (result) => DisplayResult(result); // 自定义显示结果

相关问题

struct VideoPicker: UIViewControllerRepresentable { @Environment(.presentationMode) private var presentationMode let sourceType: UIImagePickerController.SourceType // let onImagePicked: (UIImage) -> Void let onURLPicked: (URL) -> Void final class Coordinator: NSObject, UINavigationControllerDelegate, UIImagePickerControllerDelegate { @Binding private var presentationMode: PresentationMode private let sourceType: UIImagePickerController.SourceType private let onURLPicked: (URL) -> Void init(presentationMode: Binding<PresentationMode>, sourceType: UIImagePickerController.SourceType, onURLPicked: @escaping (URL) -> Void) { presentationMode = presentationMode self.sourceType = sourceType self.onURLPicked = onURLPicked } func imagePickerController( picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) { // let uiImage = info[UIImagePickerController.InfoKey.originalImage] as! UIImage // onImagePicked(uiImage) if let url = info[.mediaURL] as? URL{ onURLPicked(url) } presentationMode.dismiss() } func getVideoURL(from assetIdentifier: String, completion: @escaping (URL?) -> Void) { let fetchResult = PHAsset.fetchAssets(withLocalIdentifiers: [assetIdentifier], options: nil) guard let asset = fetchResult.firstObject else { completion(nil) return } let options = PHVideoRequestOptions() options.version = .original PHImageManager.default().requestAVAsset(forVideo: asset, options: options) { avAsset, , _ in guard let avAsset = avAsset else { completion(nil) return } let url = (avAsset as? AVURLAsset)?.url completion(url) } } func imagePickerControllerDidCancel( picker: UIImagePickerController) { presentationMode.dismiss() } } func makeCoordinator() -> Coordinator { return Coordinator(presentationMode: presentationMode, sourceType: sourceType, onURLPicked: onURLPicked) } func makeUIViewController(context: UIViewControllerRepresentableContext<VideoPicker>) -> UIImagePickerController { let picker = UIImagePickerController() picker.sourceType = sourceType picker.delegate = context.coordinator picker.mediaTypes = ["public.movie"] return picker } func updateUIViewController(_ uiViewController: UIImagePickerController, context: UIViewControllerRepresentableContext<VideoPicker>) { } }获取的url内的路径不可用

获取的 URL 可能是一个相册中的资源标识符，需要通过 PHAsset 和 PHImageManager 来获取视频的实际 URL。可以在 `Coordinator` 类中添加一个方法来获取视频的 URL，然后在 `imagePickerController(_:didFinishPickingMediaWithInfo:)` 方法中调用该方法来获取实际的 URL。

具体实现如下：

final class Coordinator: NSObject, UINavigationControllerDelegate, UIImagePickerControllerDelegate {
    // ...
    
    func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        if let assetIdentifier = info[.phAsset] as? String {
            getVideoURL(from: assetIdentifier) { url in
                if let url = url {
                    onURLPicked(url)
                }
            }
        }
        
        presentationMode.dismiss()
    }
    
    func getVideoURL(from assetIdentifier: String, completion: @escaping (URL?) -> Void) {
        let fetchResult = PHAsset.fetchAssets(withLocalIdentifiers: [assetIdentifier], options: nil)
        guard let asset = fetchResult.firstObject else {
            completion(nil)
            return
        }
        
        let options = PHVideoRequestOptions()
        options.version = .original
        
        PHImageManager.default().requestAVAsset(forVideo: asset, options: options) { avAsset, _, _ in
            guard let avAsset = avAsset else {
                completion(nil)
                return
            }
            
            let url = (avAsset as? AVURLAsset)?.url
            completion(url)
        }
    }
    
    // ...
}

这样获取到的 URL 就是实际的视频 URL，可以进行使用了。

struct VideoPicker: UIViewControllerRepresentable { @Environment(.presentationMode) private var presentationMode let sourceType: UIImagePickerController.SourceType // let onImagePicked: (UIImage) -> Void let onURLPicked: (URL) -> Void final class Coordinator: NSObject, UINavigationControllerDelegate, UIImagePickerControllerDelegate { @Binding private var presentationMode: PresentationMode private let sourceType: UIImagePickerController.SourceType private let onURLPicked: (URL) -> Void init(presentationMode: Binding<PresentationMode>, sourceType: UIImagePickerController.SourceType, onURLPicked: @escaping (URL) -> Void) { presentationMode = presentationMode self.sourceType = sourceType self.onURLPicked = onURLPicked } func imagePickerController( picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) { // let uiImage = info[UIImagePickerController.InfoKey.originalImage] as! UIImage // onImagePicked(uiImage) if let url = info[.mediaURL] as? URL{ onURLPicked(url) } presentationMode.dismiss() } func imagePickerControllerDidCancel(_ picker: UIImagePickerController) { presentationMode.dismiss() } } func makeCoordinator() -> Coordinator { return Coordinator(presentationMode: presentationMode, sourceType: sourceType, onURLPicked: onURLPicked) } func makeUIViewController(context: UIViewControllerRepresentableContext<VideoPicker>) -> UIImagePickerController { let picker = UIImagePickerController() picker.sourceType = sourceType picker.delegate = context.coordinator picker.mediaTypes = ["public.movie"] return picker } func updateUIViewController(_ uiViewController: UIImagePickerController, context: UIViewControllerRepresentableContext<VideoPicker>) { } }这段代码获取的url中绝对路径不准确

这段代码使用 UIImagePickerController 来获取视频文件的 URL，但是在 iOS 14 及以上的系统中，UIImagePickerController 获取到的视频 URL 可能会是一个 PHAsset URL，而不是真正的文件路径。

你可以使用 PHAsset 来获取真正的文件路径，具体做法是首先通过 PHAsset 的 identifier 获取 PHAsset 对象，然后使用 PHImageManager 的 requestAVAsset(forVideo:options:resultHandler:) 方法获取到 AVAsset，最后通过 AVAsset 的 url 属性获取到真正的文件路径。

下面是一个示例代码：

func getVideoURL(from assetIdentifier: String, completion: @escaping (URL?) -> Void) {
    let fetchResult = PHAsset.fetchAssets(withLocalIdentifiers: [assetIdentifier], options: nil)
    guard let asset = fetchResult.firstObject else {
        completion(nil)
        return
    }
    let options = PHVideoRequestOptions()
    options.version = .original
    PHImageManager.default().requestAVAsset(forVideo: asset, options: options) { avAsset, _, _ in
        guard let avAsset = avAsset else {
            completion(nil)
            return
        }
        let url = (avAsset as? AVURLAsset)?.url
        completion(url)
    }
}

你可以在 Coordinator 的 imagePickerController 方法中调用这个方法来获取真正的文件路径，然后将它传给 onURLPicked 回调。