我看过一些实现 template<typename T, Integer TransposedRows, Integer TransposedCols>
class Transposed<Matrix<T,TransposedRows,TransposedCols>>:
public Matrix<T,TransposedRows,TransposedCols>
{
public:
constexpr Transposed(const Matrix<T,TransposedRows,TransposedCols>& mat):
mat_ptr_(std::make_shared<Matrix<T,TransposedRows,TransposedCols>>(mat))
{}
inline constexpr const auto& operator()() const
{
return *mat_ptr_;
}
inline constexpr void operator()(cons Matrix<T,TransposedRows,TransposedCols>& mat)
{
mat_ptr_=std::make_shared<Matrix<T,TransposedRows,TransposedCols>>(mat);
}
inline constexpr T &operator()(const Integer& i, const Integer& j)
{
assert(i < Rows);
assert(j < Cols);
return (*mat_ptr_)(j,i);
}
inline constexpr const T &operator()(const Integer i, const Integer j) const
{
assert(i < Rows);
assert(j < Cols);
return (*mat_ptr_)(j,i);
}
private:
std::shared_ptr<Matrix<T,TransposedRows,TransposedCols,NonZeroRow>> mat_ptr_;
}
的示例，对我来说，以下方法是最简单的：
ICommand这就是我在测试应用程序中实现的方式。除了class Command : ICommand {
public Func<object, bool> CanDo { get; set; }
public Action<object> Do { get; set; }
public event EventHandler CanExecuteChanged {
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public Command(Func<object, bool> CanDo, Action<object> Do) {
this.CanDo = CanDo;
this.Do = Do;
}
public bool CanExecute(object parameter) => CanDo(parameter);
public void Execute(object parameter) => Do(parameter);
}
类之外，我还有以下类：
Command在class Person : INotifyPropertyChanged {
string firstName, lastName, enabled;
public string FirstName {
get => firstName;
set { firstName = value; Changed();}
}
public string LastName {
get => lastName;
set { lastName = value; Changed(); }
}
public string Enabled {
get => enabled;
set { enabled = value; Changed(); }
}
public Command MyCommand { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
public Person() {
MyCommand = new Command(CanDo, Do);
}
void Changed(string name = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
bool CanDo(object para) {
if (FirstName == "test" && LastName == "test") {
Enabled = "true";
//Changed("Enabled");
return true;
}
else {
Enabled = "false";
//Changed("Enabled");
return false;
}
}
void Do(object para) {
FirstName = "first";
LastName = "last";
}
}
中，我有这些：
xaml启动该应用程序后，如果我在<Window ...>
<Window.Resources>
<local:Person x:Key="person"/>
</Window.Resources>
<Grid DataContext="{StaticResource person}">
<StackPanel>
<TextBox Text="{Binding FirstName}"/>
<TextBox Text="{Binding LastName}"/>
<TextBlock Text="{Binding FirstName}"/>
<TextBlock Text="{Binding LastName}"/>
<Button Content="Click" Command="{Binding Path=MyCommand}"/>
<Label Content="{Binding Enabled}"/>
</StackPanel>
</Grid>
</Window>
的{{1}}中调用TextBox，则我尝试键入那些Changed()的内容都会立即被删除。如果我注释掉setter中的Enabled并取消注释Changed()中的两个setter，它会按预期工作！
在Changed("Enabled")中一次调用bool CanDo(object para)等同于在Changed()中两次调用setter吗？
答案 0 :(得分：1)
您在CallerMemberNameAttribute中缺少Changed：
void Changed([System.Runtime.CompilerServices.CallerMemberName]string name = "") =>
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
这将获取呼叫属性名称，因此您不必在设置器中呼叫Changed("Enabled")，只需呼叫Changed()。