单击标题时对ListView进行排序 [英] Sort ListView when clicking header

问题描述

我需要基于ListView标头的单击来对ListView上的内容进行排序.我正在使用C ++/CLI，所以我得到了

I need to sort the content on a ListView based on the click of the ListView header. I´m using C++/CLI, so I got the this Microsoft article and coded it using C++/CLI.

这是我的结果:

ListViewColumnSorter.h

/// <summary>
/// This class is an implementation of the 'IComparer' interface.
/// </summary>
#pragma once

public ref class ListViewColumnSorter : System::Collections::IComparer
{
    public:

        ListViewColumnSorter();
        virtual int Compare(System::Object^ x, System::Object^ y);

    private:
        /// <summary>
        /// Specifies the column to be sorted
        /// </summary>
        int ColumnToSort;

        /// <summary>
        /// Specifies the order in which to sort (i.e. 'Ascending').
        /// </summary>
        System::Windows::Forms::SortOrder OrderOfSort;

        /// <summary>
        /// Case insensitive comparer object
        /// </summary>
        System::Collections::CaseInsensitiveComparer^ ObjectCompare;

        property int SortColumn;
        property System::Windows::Forms::SortOrder SortOrder;
};

ListViewColumnSorter.cpp

/// <summary>
/// This class is an implementation of the 'IComparer' interface.
/// </summary>

#include "ListViewColumnSorter.h"

ListViewColumnSorter::ListViewColumnSorter()
{
    // Initialize the column to '0'
    ColumnToSort = 0;

    // Initialize the sort order to 'none'
    OrderOfSort = System::Windows::Forms::SortOrder::None;

    // Initialize the CaseInsensitiveComparer object
    ObjectCompare = gcnew System::Collections::CaseInsensitiveComparer();
}

/// <summary>
/// This method is inherited from the IComparer interface.  It compares the two objects passed using a case insensitive comparison.
/// </summary>
/// <param name="x">First object to be compared</param>
/// <param name="y">Second object to be compared</param>
/// <returns>The result of the comparison. "0" if equal, negative if 'x' is less than 'y' and positive if 'x' is greater than 'y'</returns>
int ListViewColumnSorter::Compare(System::Object^ x, System::Object^ y)
{
    int compareResult;
    System::Windows::Forms::ListViewItem^ listviewX, listviewY;

    // Cast the objects to be compared to ListViewItem objects
    listviewX = (System::Windows::Forms::ListViewItem^) x; <--- ERROR HERE
    listviewY = (System::Windows::Forms::ListViewItem^) y; <--- ERROR HERE

    // Compare the two items
    compareResult = ObjectCompare->Compare(listviewX->SubItems[ColumnToSort].Text,
                                           listviewY->SubItems[ColumnToSort].Text);

    // Calculate correct return value based on object comparison
    if (OrderOfSort == System::Windows::Forms:: SortOrder::Ascending)
    {
        // Ascending sort is selected, return normal result of compare operation
        return compareResult;
    }
    else if (OrderOfSort == System::Windows::Forms::SortOrder::Descending)
    {
        // Descending sort is selected, return negative result of compare operation
        return (-compareResult);
    }
    else
    {
        // Return '0' to indicate they are equal
        return 0;
    }
}

/// <summary>
/// Gets or sets the number of the column to which to apply the sorting operation (Defaults to '0').
/// </summary>
void ListViewColumnSorter::SortColumn::set(int value)
{
    ColumnToSort = value;
}

int ListViewColumnSorter::SortColumn::get()
{
    return ColumnToSort;
}

/// <summary>
/// Gets or sets the order of sorting to apply (for example, 'Ascending' or 'Descending').
/// </summary>
void ListViewColumnSorter::SortOrder::set(System::Windows::Forms::SortOrder value)
{
    OrderOfSort = value;
}

System::Windows::Forms::SortOrder ListViewColumnSorter::SortOrder::get()
{
    return OrderOfSort;
}

在比较功能上，我在编译此代码时遇到问题，在这里我无法将ListViewItem ^转换为listviewX和listviewY以获取其字符串(检查代码标记):

I´m having a problem compiling this code, on function Compare, where I cannot convert a ListViewItem^ to listviewX and listviewY to get its string (check code marker):

表达式必须具有类类型

Expression must have class type

需要解决该问题的建议.

Advice needed to solve that problem.

推荐答案

您是否正在寻找从 Object ^ 投射到 ListViewItem ^ 的正确方法?

Are you looking for the proper way to cast from Object^ to ListViewItem^?

强制转换为托管类型的通常方法是使用 dynamic_cast 或 static_cast .

The usual way to cast to a managed type is with dynamic_cast or static_cast.

我将使用 dynamic_cast< ListViewItem ^>(x)，但这确实需要您检查 nullptr .您还可以使用 static_cast< ListViewItem ^>(x)，如果类型不正确，则会抛出异常.

I would use dynamic_cast<ListViewItem^>(x), but that does require that you check for nullptr. You could also use static_cast<ListViewItem^>(x), which will throw an exception if it's not of the proper type.

此外，请注意，没有什么可以阻止您在C#中实现 ListViewColumnSorter 类，并从C ++/CLI中引用它.

Also, note that there's nothing stopping you from implementing the ListViewColumnSorter class in C#, and referencing that from C++/CLI.

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