C＃将过滤器添加到组合框下拉列表 [英] C# Adding Filter to combobox dropdown list

问题描述

在向我的 ComboBox 下拉列表中添加过滤器时需要一些帮助（Windows Forms Visual Studio 2015）

Need some help with adding filter to my ComboBox drop down list(windows Forms Visual studio 2015)

下拉列表如下所示：

public ReconciliationReport()
{
    InitializeComponent();
    AppDomain.CurrentDomain.AssemblyResolve += FindDLL;

    this.sRootDirectory = Properties.Resources.sRootDirectory;

    string[] arrProjectList = Directory.GetDirectories(sRootDirectory).Select(Directory => Path.GetFileName(Directory)).ToArray();
    Array.Sort(arrProjectList);

    int iProjectCount = arrProjectList.Length;
    this.DropDownListSize = iProjectCount;

    for (int i = 0; i < iProjectCount; i++)
    {
        SelectJobDropdown.Items.Add(arrProjectList[i]);
    }
}

这给了我一个不错的下拉列表目录。

This gives me a nice drop down list of all current directories.

现在，我需要添加一个文件管理器以仅显示包含键入到 ComboBox 本身，而不管下拉列表本身是否打开。

Now, I need to add a filer to show only items which contain a text typed into the ComboBoxitself regardless if the dropdown list itself is open or not.

我同时禁用了 AutoCompleteMode 和 AutoCompleteSource 在打开的下拉列表中无法正常工作。它是在现有列表的顶部打开附加列表，但我只能从其下面的下拉列表中进行选择。请参见下面的打印屏幕：

I have disabled both AutoCompleteMode and AutoCompleteSource as it was not working as expected with the opened droped down list. It was opening additonal list on top the existing one but I could only select from the dropdown under it. See print screen below:

顶部的列表处于非活动状态，我既不能选择文本，也可以选择文本没有提供显示子字符串的选项。

The list on top is inactive and I cannot select the text but also does not give an option to display substrings.

盒子本身只有一个，甚至是

Only have one even for the box itself which is

private void SelectJobDropdown_SelectedIndexChanged(object sender, EventArgs e) 
{
    //Plenty of code here 
}

有人在我输入框内内容时可以指出正确的方向如何过滤列表。

Can someone point in the right direction how to filter the list as I type within the box itself.

请注意，我一直在使用C＃仅仅三个星期，所以可能会与该语言的某些术语或其他方面混淆。

Please NOTE I have been using C# for only 3 weeks so might get confused with some of the terminology or other aspects of this language etc.

推荐答案

我建议使用2个列表。原始值1

I would suggest to use 2 Lists. 1 for the original values

List<string> arrProjectList;

public ReconciliationReport()
{
    InitializeComponent();
    AppDomain.CurrentDomain.AssemblyResolve += FindDLL;

    this.sRootDirectory = Properties.Resources.sRootDirectory;

    arrProjectList = Directory.GetDirectories(sRootDirectory).Select(Directory => Path.GetFileName(Directory)).ToList();
    arrProjectList.Sort();

    // then just bind it to the DataSource of the ComboBox
    SelectJobDropdown.DataSource = arrProjectList;
    // don't select automatically the first item
    SelectJobDropdown.SelectedIndex = -1;
}

，过滤后的值是1。在此示例中，我使用 TextBox 捕获过滤器文本。在 TextChanged 事件中，获取过滤器文本并仅从原始 arrProjectList 列表中拉出那些值。如果过滤器为空，则最后需要一个额外的选项来将绑定重置为旧列表。

and 1 for the filtered values. In this example I use a TextBox to catch the filter text. In the TextChanged event take the filter text and pull out only those values from the original arrProjectList List. You would need an extra option at the end to reset the binding to the old list if the filter is empty.

private void textBox1_TextChanged(object sender, EventArgs e)
{
    string filter_param = textBox1.Text;

    List<string> filteredItems = arrProjectList.FindAll(x => x.Contains(filter_param));
    // another variant for filtering using StartsWith:
    // List<string> filteredItems = arrProjectList.FindAll(x => x.StartsWith(filter_param));

    comboBox1.DataSource = filteredItems;

    // if all values removed, bind the original full list again
    if (String.IsNullOrWhiteSpace(textBox1.Text))
    {
        comboBox1.DataSource = arrProjectList;
    }

    // this line will make sure, that the ComboBox opens itself to show the filtered results       
}

编辑

我找到了在 ComboBox 直接。过滤过程相同，但是使用 TextUpdate 事件，有必要取消选择 SelectedIndex ，该事件会自动设置为绑定后的第一个元素。然后，我想您想继续编写过滤器（不止一个字母），将过滤器写回到 ComboBox.Text 属性中，并将光标位置设置为末尾：

I found a Solution for typing the filter into the ComboBox directly. The filtering is the same procedure, but using the TextUpdate event it is necessary to unselect the SelectedIndex which is automatically set to the first element after the binding. Then I guess you want to proceed to write your filter (more than just one letter), write the filter back into the ComboBox.Text property and set the cursor position to the end:

private void comboBox1_TextUpdate(object sender, EventArgs e)
{
    string filter_param = comboBox1.Text;

    List<string> filteredItems = arrProjectList.FindAll(x => x.Contains(filter_param));
    // another variant for filtering using StartsWith:
    // List<string> filteredItems = arrProjectList.FindAll(x => x.StartsWith(filter_param));

    comboBox1.DataSource = filteredItems;

    if (String.IsNullOrWhiteSpace(filter_param))
    {
        comboBox1.DataSource = arrProjectList;
    }
    comboBox1.DroppedDown = true;

    // this will ensure that the drop down is as long as the list
    comboBox1.IntegralHeight = true;

    // remove automatically selected first item
    comboBox1.SelectedIndex = -1;

    comboBox1.Text = filter_param;

    // set the position of the cursor
    comboBox1.SelectionStart = filter_param.Length;
    comboBox1.SelectionLength = 0;            
}

Etvoilà自动过滤，并带有漂亮的显示和随后的箭头选择。

Et voilà automatic filtering with a nice display and arrow selection afterwards.

编辑2

对于不区分大小写的搜索，可以使用以下方法：

for case insensitive search you can use this:

List<string> filteredItems = arrProjectList.FindAll(x => x.ToLower().Contains(filter_param.ToLower()));

注意：

在下拉列表中，光标将消失。为了防止这种情况，必须将 Cursor.Current 设置为 Cursor.Defualt

After the opening of the dropdownlist the cursor will disappear. To prevent this the Cursor.Current has to be set to Cursor.Defualt

comboBox1.DroppedDown = true;
Cursor.Current = Cursors.Default;

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