工作记录

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MarkupExtension:XAML标记扩展

实现了什么作用：通过扩展标记将一种输入转化为另一种类型的输出

思路：

不直接设置控件的Visibility属性，利用一个标记扩展，传入一个权限值，然后拿这个权限值跟当前程序的用户权限对比，如果控件的权限值高于当前用户权限（比如控件的权限值是管理员，但是当前用户是普通用户），则返回Visibility.Collapsed，反之返回Visibility.Visible。

代码：

[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));//控件对象targetObject = (FrameworkElement)providerValuetarget.TargetObject;//元素布局事件targetObject.Loaded += TargetObject_Loaded;//元素删除事件targetObject.Unloaded += TargetObject_Unloaded;//标记的控件属性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是提供了权限变更处理方法的接口：

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

PermissionService是程序的权限管理类，保存着相关控件的扩展标记，提供了挂载方法：

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);}
}

当PermissionService类中的用户权限改变时，会遍历listeners 中的扩展，触发PermissionChanged方法：

 private static void OnPermissionChanged(){foreach (var it in listeners){//authority是当前类中的属性，表示用户权限it.PermissionChanged(authority);}}

每个扩展中的PermissionChanged方法：

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

通过控件直接设置属性值实现改变控件可见状态；

前端写法：

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

引用：笔记：WPF中MarkupExtension使用的IServiceProvider参数都有哪些_wpf iserviceprovider-CSDN博客

WPF基础之Binding解析_calcbinding-CSDN博客