工作記錄

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MarkupExtension:XAML標記擴展

實現了什么作用：通過擴展標記將一種輸入轉化為另一種類型的輸出

思路：

不直接設置控件的Visibility屬性，利用一個標記擴展，傳入一個權限值，然后拿這個權限值跟當前程序的用戶權限對比，如果控件的權限值高于當前用戶權限（比如控件的權限值是管理員，但是當前用戶是普通用戶），則返回Visibility.Collapsed，反之返回Visibility.Visible。

代碼：

[MarkupExtensionReturnType(typeof(Visibility))]
public class PermissionVisibleExtension : MarkupExtension, IPermissionListener
{private FrameworkElement targetObject;private DependencyProperty targetProperty;[ConstructorArgument("authority")]public Authority Authority { get; set; }public PermissionVisibleExtension(){}public PermissionVisibleExtension(Authority authority){Authority = authority;}public override object ProvideValue(IServiceProvider serviceProvider){try{var providerValuetarget = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));//控件對象targetObject = (FrameworkElement)providerValuetarget.TargetObject;//元素布局事件targetObject.Loaded += TargetObject_Loaded;//元素刪除事件targetObject.Unloaded += TargetObject_Unloaded;//標記的控件屬性targetProperty = (DependencyProperty)providerValuetarget.TargetProperty;PermissionService.AddListener(this);return PermissionService.Authority >= Authority ? Visibility.Visible : Visibility.Collapsed;}catch (Exception){return Visibility.Collapsed;}}private void TargetObject_Loaded(object sender, RoutedEventArgs e){PermissionService.AddListener(this);PermissionChanged(PermissionService.Authority);}private void TargetObject_Unloaded(object sender, RoutedEventArgs e){PermissionService.RemoveListener(this);}public void PermissionChanged(Authority authority){targetObject.SetCurrentValue(targetProperty, PermissionService.Authority >= Authority ? Visibility.Visible : Visibility.Collapsed);}
}

其中IPermissionListener是提供了權限變更處理方法的接口：

public interface IPermissionListener
{void PermissionChanged(Authority authority);
}

PermissionService是程序的權限管理類，保存著相關控件的擴展標記，提供了掛載方法：

private static readonly List<IPermissionListener> listeners = new List<IPermissionListener>();
public static void AddListener(IPermissionListener listener)
{if (!listeners.Contains(listener)){listeners.Add(listener);}
}public static void RemoveListener(IPermissionListener listener)
{if (listeners.Contains(listener)){listeners.Remove(listener);}
}

當PermissionService類中的用戶權限改變時，會遍歷listeners 中的擴展，觸發PermissionChanged方法：

 private static void OnPermissionChanged(){foreach (var it in listeners){//authority是當前類中的屬性，表示用戶權限it.PermissionChanged(authority);}}

每個擴展中的PermissionChanged方法：

public void PermissionChanged(Authority authority)
{targetObject.SetCurrentValue(targetProperty, PermissionService.Authority >= Authority ? Visibility.Visible : Visibility.Collapsed);
}

通過控件直接設置屬性值實現改變控件可見狀態；

前端寫法：

 Visibility="{view:PermissionVisible Authority=Expert}">

引用：筆記：WPF中MarkupExtension使用的IServiceProvider參數都有哪些_wpf iserviceprovider-CSDN博客

WPF基礎之Binding解析_calcbinding-CSDN博客