/// <summary>
/// 确定此命令是否可在其当前状态下执行的方法。
/// WPF 中触发 CanExecute 的条件：
/// 1. 获取键盘焦点时
/// 2. Execute 调用前
/// 3. Execute 调用后。
/// </summary>
/// <param name="parameter"></param>
/// <returns></returns>
public virtual bool CanExecute(object parameter)
{
// 仅在第一次获取键盘焦点时，执行 CanExecuteDelegate
if (IsFirstKeyboardFocus)
{
// 备注：使用关键字 async 返回的 Task 会自动执行
IsCan = CanExecuteDelegate?.Invoke(parameter) ?? true;
IsFirstKeyboardFocus = false;
}
return(Can());
}
protected override bool CanExecute(object parameter)
{
try
{
return(CanExecuteDelegate?.Invoke() ?? true);
}
catch (Exception ex)
{
_registry.HandledException(ex);
return(false);
}
}
protected override bool CanExecute(object parameter)
{
try
{
T param = default;
if (parameter is T TParam)
{
param = TParam;
}
else if (parameter != null && ThrowOnInvalidCast)
{
throw new InvalidCastException($"The Command expected a typeof '{typeof(T).FullName}' but recieved a parameter of type '{parameter.GetType().FullName}");
}
return(CanExecuteDelegate?.Invoke(param) ?? true);
}
catch (Exception ex)
{
_registry.HandledException(ex);
return(false);
}
}
/// <summary> /// A RelayCommand can always execute. /// </summary> /// <param name="parameter"></param> /// <returns></returns> public bool CanExecute(object parameter) => CanExecuteDelegate?.Invoke() ?? true;
public bool CanExecute(object parameter)
{
return(CanExecuteDelegate?.Invoke(parameter) ?? true);
}
