整理整理

AIStudio.Wpf.DiagramDesigner.Additionals/Commands/DelegateCommand(T).cs

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+using System;
+using System.Linq.Expressions;
+using System.Reflection;
+using System.Windows.Input;
+
+namespace AIStudio.Wpf.DiagramDesigner.Additionals.Commands
+{
+    /// <summary>
+    /// An <see cref="ICommand"/> whose delegates can be attached for <see cref="Execute(T)"/> and <see cref="CanExecute(T)"/>.
+    /// </summary>
+    /// <typeparam name="T">Parameter type.</typeparam>
+    /// <remarks>
+    /// The constructor deliberately prevents the use of value types.
+    /// Because ICommand takes an object, having a value type for T would cause unexpected behavior when CanExecute(null) is called during XAML initialization for command bindings.
+    /// Using default(T) was considered and rejected as a solution because the implementor would not be able to distinguish between a valid and defaulted values.
+    /// <para/>
+    /// Instead, callers should support a value type by using a nullable value type and checking the HasValue property before using the Value property.
+    /// <example>
+    ///     <code>
+    /// public MyClass()
+    /// {
+    ///     this.submitCommand = new DelegateCommand&lt;int?&gt;(this.Submit, this.CanSubmit);
+    /// }
+    /// 
+    /// private bool CanSubmit(int? customerId)
+    /// {
+    ///     return (customerId.HasValue &amp;&amp; customers.Contains(customerId.Value));
+    /// }
+    ///     </code>
+    /// </example>
+    /// </remarks>
+    public class DelegateCommand<T> : DelegateCommandBase
+    {
+        readonly Action<T> _executeMethod;
+        Func<T, bool> _canExecuteMethod;
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="DelegateCommand{T}"/>.
+        /// </summary>
+        /// <param name="executeMethod">Delegate to execute when Execute is called on the command. This can be null to just hook up a CanExecute delegate.</param>
+        /// <remarks><see cref="CanExecute(T)"/> will always return true.</remarks>
+        public DelegateCommand(Action<T> executeMethod)
+            : this(executeMethod, (o) => true)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="DelegateCommand{T}"/>.
+        /// </summary>
+        /// <param name="executeMethod">Delegate to execute when Execute is called on the command. This can be null to just hook up a CanExecute delegate.</param>
+        /// <param name="canExecuteMethod">Delegate to execute when CanExecute is called on the command. This can be null.</param>
+        /// <exception cref="ArgumentNullException">When both <paramref name="executeMethod"/> and <paramref name="canExecuteMethod"/> are <see langword="null" />.</exception>
+        public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
+            : base()
+        {
+            if (executeMethod == null || canExecuteMethod == null)
+                throw new ArgumentNullException(nameof(executeMethod), "DelegateCommandDelegatesCannotBeNull");
+
+            TypeInfo genericTypeInfo = typeof(T).GetTypeInfo();
+
+            // DelegateCommand allows object or Nullable<>.  
+            // note: Nullable<> is a struct so we cannot use a class constraint.
+            if (genericTypeInfo.IsValueType)
+            {
+                if ((!genericTypeInfo.IsGenericType) || (!typeof(Nullable<>).GetTypeInfo().IsAssignableFrom(genericTypeInfo.GetGenericTypeDefinition().GetTypeInfo())))
+                {
+                    throw new InvalidCastException("DelegateCommandInvalidGenericPayloadType");
+                }
+            }
+
+            _executeMethod = executeMethod;
+            _canExecuteMethod = canExecuteMethod;
+        }
+
+        ///<summary>
+        ///Executes the command and invokes the <see cref="Action{T}"/> provided during construction.
+        ///</summary>
+        ///<param name="parameter">Data used by the command.</param>
+        public void Execute(T parameter)
+        {
+            _executeMethod(parameter);
+        }
+
+        ///<summary>
+        ///Determines if the command can execute by invoked the <see cref="Func{T,Bool}"/> provided during construction.
+        ///</summary>
+        ///<param name="parameter">Data used by the command to determine if it can execute.</param>
+        ///<returns>
+        ///<see langword="true" /> if this command can be executed; otherwise, <see langword="false" />.
+        ///</returns>
+        public bool CanExecute(T parameter)
+        {
+            return _canExecuteMethod(parameter);
+        }
+
+        /// <summary>
+        /// Handle the internal invocation of <see cref="ICommand.Execute(object)"/>
+        /// </summary>
+        /// <param name="parameter">Command Parameter</param>
+        protected override void Execute(object parameter)
+        {
+            Execute((T)parameter);
+        }
+
+        /// <summary>
+        /// Handle the internal invocation of <see cref="ICommand.CanExecute(object)"/>
+        /// </summary>
+        /// <param name="parameter"></param>
+        /// <returns><see langword="true"/> if the Command Can Execute, otherwise <see langword="false" /></returns>
+        protected override bool CanExecute(object parameter)
+        {
+            return CanExecute((T)parameter);
+        }
+
+        /// <summary>
+        /// Observes a property that implements INotifyPropertyChanged, and automatically calls DelegateCommandBase.RaiseCanExecuteChanged on property changed notifications.
+        /// </summary>
+        /// <typeparam name="TType">The type of the return value of the method that this delegate encapulates</typeparam>
+        /// <param name="propertyExpression">The property expression. Example: ObservesProperty(() => PropertyName).</param>
+        /// <returns>The current instance of DelegateCommand</returns>
+        public DelegateCommand<T> ObservesProperty<TType>(Expression<Func<TType>> propertyExpression)
+        {
+            ObservesPropertyInternal(propertyExpression);
+            return this;
+        }
+
+        /// <summary>
+        /// Observes a property that is used to determine if this command can execute, and if it implements INotifyPropertyChanged it will automatically call DelegateCommandBase.RaiseCanExecuteChanged on property changed notifications.
+        /// </summary>
+        /// <param name="canExecuteExpression">The property expression. Example: ObservesCanExecute(() => PropertyName).</param>
+        /// <returns>The current instance of DelegateCommand</returns>
+        public DelegateCommand<T> ObservesCanExecute(Expression<Func<bool>> canExecuteExpression)
+        {
+            Expression<Func<T, bool>> expression = System.Linq.Expressions.Expression.Lambda<Func<T, bool>>(canExecuteExpression.Body, System.Linq.Expressions.Expression.Parameter(typeof(T), "o"));
+            _canExecuteMethod = expression.Compile();
+            ObservesPropertyInternal(canExecuteExpression);
+            return this;
+        }
+    }
+}