SwiftUI 状态变量不渲染视图，除非在视图内部使用（修改器中的诗句）

Question

抱歉措辞糟糕，但在 onAppear 中我正在更改状态变量，但是除非我在视图内的某处使用该状态变量，否则这不会重新渲染视图。

如果用户未登录，我会尝试弹出一个模式，但除非我将变量放入视图中，否则它不会弹出，如下所示

struct SearchView: View {
// Environment Variables
@EnvironmentObject var session: SessionStore

@State var sheetIsPresented: Bool = false

var body: some View {
    NavigationView {
        // Just having a line like this will cause it to work
        if self.sheetIsPresented || !self.sheetIsPresented {}
    }
    .onAppear {
        if self.session.userSession != nil {
            self.sheetIsPresented = true
        }
    }
    .sheet(isPresented: $sheetIsPresented) {
        WelcomeSignInModal(sheetIsPresented: self.$sheetIsPresented)
    }
}
}

Answer 1

您可以尝试以下演示：

class SessionStore: ObservableObject {
    var userSession: String? = "session"
}

struct ContentView: View {
    @EnvironmentObject var session: SessionStore

    @State var sheetIsPresented: Bool = false

    var body: some View {
        NavigationView {
            Text("SearchView")
        }
        .onAppear {
            self.sheetIsPresented = self.session.userSession != nil
        }
        .sheet(isPresented: $sheetIsPresented) {
            Text("WelcomeSignInModal")
        }
    }
}

使用 Xcode 11.6、iOS 13.6 测试