我有这个代码，显示PDF，PDF加载良好。但是，我添加了一个工具栏按钮来将PDF更改为不同的文件，但它不起作用。我没有收到任何错误消息，但视图没有更新以显示新文件。

import SwiftUI
import PDFKit

struct PDFKitRepresentedView: UIViewRepresentable {
    let url: URL
    let pdfView = PDFView()
    
    init(_ url: URL) {
        self.url = url
        pdfView.document = PDFDocument(url: self.url)
    }

    func makeUIView(context: UIViewRepresentableContext<PDFKitRepresentedView>) -> PDFKitRepresentedView.UIViewType {
        return pdfView
    }

    func updateUIView(_ uiView: UIView, context: UIViewRepresentableContext<PDFKitRepresentedView>) {
    }
}

struct PDFKitView: View {
    var url: URL
    var body: some View {
        PDFKitRepresentedView(url)
    }
}

struct ContentView: View {
    
    @State var documentURL = Bundle.main.url(forResource: "file1", withExtension: "pdf")!
    
    var body: some View {
        
        NavigationStack {
            PDFKitView(url: documentURL)
            .toolbar {
                Button("Change PDF") {
                    documentURL = Bundle.main.url(forResource: "file2", withExtension: "pdf")!
                }
            }
        }
    }
}