ICommand 介面

  • 參考

定義

命名空間:
Windows.UI.Xaml.Input
編輯

定義互動式 UI 元素的命令列為，該元素會在叫用時執行動作，例如傳送電子郵件、刪除專案或提交表單。

public interface class ICommand
/// [Windows.Foundation.Metadata.ContractVersion(Windows.Foundation.UniversalApiContract, 65536)]
/// [Windows.Foundation.Metadata.Guid(3853464898, 51815, 16513, 153, 91, 112, 157, 209, 55, 146, 223)]
struct ICommand
[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 65536)]
[Windows.Foundation.Metadata.Guid(3853464898, 51815, 16513, 153, 91, 112, 157, 209, 55, 146, 223)]
public interface ICommand
Public Interface ICommand
屬性
ContractVersionAttribute GuidAttribute

Windows 需求

裝置系列
Windows 10 (已於 10.0.10240.0 引進)
API contract
Windows.Foundation.UniversalApiContract (已於 v1.0 引進)

範例

在這裡，我們會定義只將其功能轉寄給其他物件的命令。

如需完整的應用程式，請參閱 UI 基本概念 (XAML) 範例 。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
namespace AppUIBasics.Common
{
    /// <summary>
    /// A command whose sole purpose is to relay its functionality
    /// to other objects by invoking delegates.
    /// The default return value for the CanExecute method is 'true'.
    /// RaiseCanExecuteChanged needs to be called whenever
    /// CanExecute is expected to return a different value.
    /// </summary>
    public class RelayCommand : ICommand
    {
        private readonly Action _execute;
        private readonly Func<bool> _canExecute;
        /// <summary>
        /// Raised when RaiseCanExecuteChanged is called.
        /// </summary>
        public event EventHandler CanExecuteChanged;
        /// <summary>
        /// Creates a new command that can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        public RelayCommand(Action execute)
            : this(execute, null)
        {
        }
        /// <summary>
        /// Creates a new command.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        public RelayCommand(Action execute, Func<bool> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("execute");
            _execute = execute;
            _canExecute = canExecute;
        }
        /// <summary>
        /// Determines whether this RelayCommand can execute in its current state.
        /// </summary>
        /// <param name="parameter">
        /// Data used by the command. If the command does not require data to be passed,
        /// this object can be set to null.
        /// </param>
        /// <returns>true if this command can be executed; otherwise, false.</returns>
        public bool CanExecute(object parameter)
        {
            return _canExecute == null ? true : _canExecute();
        }
        /// <summary>
        /// Executes the RelayCommand on the current command target.
        /// </summary>
        /// <param name="parameter">
        /// Data used by the command. If the command does not require data to be passed,
        /// this object can be set to null.
        /// </param>
        public void Execute(object parameter)
        {
            _execute();
        }
        /// <summary>
        /// Method used to raise the CanExecuteChanged event
        /// to indicate that the return value of the CanExecute
        /// method has changed.
        /// </summary>
        public void RaiseCanExecuteChanged()
        {
            var handler = CanExecuteChanged;
            if (handler != null)
            {
                handler(this, EventArgs.Empty);
            }
        }
    }
}

備註

XamlUICommand 會針對 C++ 或 System.Windows.Input.ICommand 實作此 ICommand 介面， (新增各種 UI 屬性、方法和事件) 。

如需基本範例，請參閱 Button 控制項，當使用者按一下該控制項時會叫用命令。 管理命令體驗的方式有兩種：

  • 處理 Click 事件
  • 將 Command 屬性系結至描述命令邏輯的 ICommand 實作

方法

CanExecute(Object)

擷取命令是否可以在其目前狀態中執行。
Execute(Object)

定義叫用命令時要呼叫的方法。

事件

CanExecuteChanged

每當發生會影響命令是否可以執行的情況時發生。

適用於

另請參閱