使用 ListBox 缓慢显示/绘制对话? [英] Slow showing / drawing dialogue with ListBox?

问题描述

我的应用程序使用实体框架来提取一小部分结果......它需要大约 3 秒才能完成?为什么会这样?

My application uses entity framework to pull in a small tiny set of results... It takes about 3 seconds for it to do it? Why might this be?

Start.cs

...
private void projectToolStripMenuItem_Click(object sender, System.EventArgs e)
{
    NewProject newProjectForm = new NewProject();
    newProjectForm.ShowDialog(); // It seems to take about 3 or 4 seconds to actually get to this :S
}
...

NewProject.cs

public partial class NewProject : Form
{
    private EFProjectTypeRepository projectTypeRepository;

    public NewProject()
    {
        projectTypeRepository = new EFProjectTypeRepository();

        InitializeComponent();
        ListBoxProjectTypes();
    }

    public void ListBoxProjectTypes()
    {    
        DateTime then = DateTime.Now;

        // PreLoadedResources.projectTypes is a preloaded resource which takes split seconds to load.

        ListBoxProjectType.Items.AddRange(PreLoadedResources.projectTypes.Select(item => (object)item.Title).ToArray()); // If I comment this line out, the dialogue is almost instant @ timeTaken  {00:00:00.0010019}

        DateTime now = DateTime.Now;
        TimeSpan timeTaken = now.Subtract(then); 
    }
}

:

timeTaken   {00:00:02.4261369}  System.TimeSpan

当我第二次去展示对话时，它是即时的！

when I go and show the dialogue a second time, it's instant!

到目前为止，我的列表框显示了 1 个项目，哈哈.

注意事项:

public static class PreLoadedResources
{
    public static IEnumerable<ProjectType> projectTypes;
}

推荐答案

ListBox 必须在每次添加项目时重绘.您可以使用 Dmitry 使用 AddRange() 的方法，也可以使用 BeginUpdate()/EndUpdate() 调用来包装循环.

The ListBox has to redraw every time you add an item. You can either use Dmitry's method of using AddRange(), or you can wrap your loop with BeginUpdate()/EndUpdate() calls.

ListBoxProjectType.BeginUpdate();

foreach( var projectType in projectTypes )
{
    ListBoxProjectType.Items.Add(projectType.Title);
}

ListBoxProjectType.EndUpdate();

这篇关于使用 ListBox 缓慢显示/绘制对话?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！