为什么当堆栈中有操作时，@Environment UndoManager不更新其canUndo属性？我有一个视图，该视图的子级可以使用撤消/重做功能，但是由于某种原因，我无法基于管理器禁用撤消按钮。
struct MyView: View {
@Environment(\.undoManager) var undoManager: UndoManager?
var body: some View {
Button("Undo") { ... }
.disabled(!self.undoManager!.canUndo)
}
}
UndoManager.canUndo 不符合KVO，因此请使用某些通知发布者来跟踪状态，如下所示
struct MyView: View {
@Environment(\.undoManager) var undoManager
@State private var canUndo = false
// consider also other similar notifications
private let undoObserver = NotificationCenter.default.publisher(for: .NSUndoManagerDidCloseUndoGroup)
var body: some View {
Button("Undo") { }
.disabled(!canUndo)
.onReceive(undoObserver) { _ in
self.canUndo = self.undoManager!.canUndo
}
}
}
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