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        使用 ListBox 缓慢显示/绘制对话?

        Slow showing / drawing dialogue with ListBox?(使用 ListBox 缓慢显示/绘制对话?)

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                  本文介绍了使用 ListBox 缓慢显示/绘制对话?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                  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跟版网!

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