.net - 如何异步获取文本框的自动完成数据？

Question

我们的WinForms应用程序会延迟加载数据以自动完成文本框。其伪代码如下；

1. 用户在文本框中输入内容
2. 在输入暂停时，确定我们是否需要获取自动完成数据
3. 在工作线程中，联系服务器并获取数据
4. 调用回 UI 线程
5. 设置textBox.AutoCompleteCustomSource = fetchedAutoCompleteStringCollection;
6. 强制文本框下拉其自动完成下拉列表。

我目前遇到了#6 的问题。作为黑客，我执行以下操作来模拟有效的按键，但并非在所有情况下都有效。

     // This is a hack, but the only way that I have found to get the autocomplete
     // to drop down once the data is returned.
     textBox.SelectionStart = textBox.Text.Length;
     textBox.SelectionLength = 0;
     SendKeys.Send( " {BACKSPACE}" );

一定有更好的方法。我不敢相信我是唯一一个异步获取自动完成数据的人。我应该怎么做？

编辑: 用于导致自动完成下拉列表的 Win32 调用是可以接受的。如果有必要，我不介意 PInvoking。

Answer 1

我仅使用托管代码为 TextBox 编写了一个异步自动完成类。希望对您有所帮助。

using System;
using System.Windows.Forms;
using System.Collections.Generic;
using System.Text;
using System.ComponentModel;

namespace TextboxAutocomplete
{
    public abstract class AutoCompleteSource
    {
        private TextBox mTextBox;
        private AutoCompleteMode mAutoCompleteMode;

        public AutoCompleteSource(TextBox textbox) :
            this(textbox, AutoCompleteMode.Suggest) { }

        public AutoCompleteSource(TextBox textbox, AutoCompleteMode mode)
        {
            if (textbox == null)
                throw new ArgumentNullException("textbox");

            if (textbox.IsDisposed)
                throw new ArgumentException("textbox");

            mTextBox = textbox;
            mAutoCompleteMode = mode;

            mTextBox.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.None;

            BackgroundWorker autoCompleteLoader = new BackgroundWorker();
            autoCompleteLoader.DoWork += new DoWorkEventHandler(autoCompleteLoader_DoWork);
            autoCompleteLoader.RunWorkerCompleted += new RunWorkerCompletedEventHandler(autoCompleteLoader_RunWorkerCompleted);
            autoCompleteLoader.RunWorkerAsync();
        }

        void autoCompleteLoader_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            AutoCompleteStringCollection collection = e.Result as AutoCompleteStringCollection;
            if (collection == null) return;

            if (mTextBox.InvokeRequired)
            {
                mTextBox.Invoke(new SetAutocompleteSource(DoSetAutoCompleteSource), new object[] { collection });
            }
            else
            {
                DoSetAutoCompleteSource(collection);
            }
        }

        protected void DoSetAutoCompleteSource(AutoCompleteStringCollection collection)
        {
            if (mTextBox.IsDisposed) return;

            mTextBox.AutoCompleteMode = mAutoCompleteMode;
            mTextBox.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.CustomSource;
            mTextBox.AutoCompleteCustomSource = collection;
        }

        void autoCompleteLoader_DoWork(object sender, DoWorkEventArgs e)
        {
            List<string> autoCompleteItems = GetAutocompleteItems();
            if (autoCompleteItems == null) return;
            AutoCompleteStringCollection collection = new AutoCompleteStringCollection();
            collection.AddRange(GetAutocompleteItems().ToArray());
            e.Result = collection;
        }

        protected abstract List<string> GetAutocompleteItems();
    }

    internal delegate void SetAutocompleteSource(AutoCompleteStringCollection collection);
}

示例实现:

using System;
using System.Windows.Forms;
using System.Collections.Generic;
using System.Text;

namespace TextboxAutocomplete
{
    class MockAutoCompleteSource : AutoCompleteSource
    {
        public MockAutoCompleteSource(TextBox textbox)
            : base(textbox)
        {

        }

        protected override List<string> GetAutocompleteItems()
        {
            List<string> result = new List<string>();
            for (int i = 0; i < 2500; i++)
            {
                result.Add(Guid.NewGuid().ToString());
            }

            return result;
        }
    }
}

如何使用:

 ...
 TextBox myTextbox = new TextBox();
 MockAutoCompleteSource autoComplete =
      new MockAutoCompleteSource(myTextbox);
 ...