如何让ComboBox的下拉列表宽度自适应内容的宽度

╰+哭是因爲堅強的太久メ 2022-01-07 15:45 285阅读 0赞

在Win Form编程中，ComboBox是我们经常用到的控件，往往因为界面排版或者其它原因，ComboBox的宽度受到限制，而下拉列表中的内容太长。 如果按照 ComboBox 的默认设置 ，下拉列表和 ComboBox 的宽度一样，并不会跟随内容的变化而变化，这就造成下拉列表中有些项的内容太长而不能全部显示出来，就是下面这个样子：  
![5\_1.JPG][5_1.JPG]  
  
如果能够让下拉列表的宽度随着内容的变化而变化，这个问题不就解决了。下面我们看看如何让 ComboBox的下拉列表宽度自适应内容的宽度：

1 ![None.gif][] private   void  AdjustComboBoxDropDownListWidth( object  comboBox)  
  2 ![ExpandedBlockStart.gif][None.gif]![ContractedBlock.gif][None.gif] ![dot.gif][None.gif] \{  
 3![InBlock.gif][None.gif]    Graphics g = null;  
 4![InBlock.gif][None.gif]    Font font = null;  
 5![InBlock.gif][None.gif]    try  
 6![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]    ![dot.gif][None.gif]\{  
 7![InBlock.gif][None.gif]        ComboBox senderComboBox = null;  
 8![InBlock.gif][None.gif]        if (comboBox is ComboBox)  
 9![InBlock.gif][None.gif]            senderComboBox = (ComboBox)comboBox;  
10![InBlock.gif][None.gif]        else if (comboBox is ToolStripComboBox)  
11![InBlock.gif][None.gif]            senderComboBox = ((ToolStripComboBox)comboBox).ComboBox;  
12![InBlock.gif][None.gif]        else  
13![InBlock.gif][None.gif]            return;  
14![InBlock.gif][None.gif]  
15![InBlock.gif][None.gif]        int width = senderComboBox.Width;  
16![InBlock.gif][None.gif]        g = senderComboBox.CreateGraphics();  
17![InBlock.gif][None.gif]        font = senderComboBox.Font;  
18![InBlock.gif][None.gif]  
19![InBlock.gif][None.gif]        //checks if a scrollbar will be displayed.  
20![InBlock.gif][None.gif]        //If yes, then get its width to adjust the size of the drop down list.  
21![InBlock.gif][None.gif]        int vertScrollBarWidth =  
22![InBlock.gif][None.gif]            (senderComboBox.Items.Count > senderComboBox.MaxDropDownItems)  
23![InBlock.gif][None.gif]            ? SystemInformation.VerticalScrollBarWidth : 0;  
24![InBlock.gif][None.gif]  
25![InBlock.gif][None.gif]        int newWidth;  
26![InBlock.gif][None.gif]        foreach (object s in senderComboBox.Items)  //Loop through list items and check size of each items.  
27![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]        ![dot.gif][None.gif]\{  
28![InBlock.gif][None.gif]            if (s != null)  
29![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]            ![dot.gif][None.gif]\{  
30![InBlock.gif][None.gif]                newWidth = (int)g.MeasureString(s.ToString().Trim(), font).Width  
31![InBlock.gif][None.gif]                    \+ vertScrollBarWidth;  
32![InBlock.gif][None.gif]                if (width < newWidth)  
33![InBlock.gif][None.gif]                    width = newWidth;   //set the width of the drop down list to the width of the largest item.  
34![ExpandedSubBlockEnd.gif][None.gif]            \}  
35![ExpandedSubBlockEnd.gif][None.gif]        \}  
36![InBlock.gif][None.gif]        senderComboBox.DropDownWidth = width;  
37![ExpandedSubBlockEnd.gif][None.gif]    \}  
38![InBlock.gif][None.gif]    catch  
39![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]    ![dot.gif][None.gif]\{ \}  
40![InBlock.gif][None.gif]    finally  
41![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]    ![dot.gif][None.gif]\{  
42![InBlock.gif][None.gif]        if (g != null)  
43![InBlock.gif][None.gif]            g.Dispose();  
44![ExpandedSubBlockEnd.gif][None.gif]    \}  
45![ExpandedBlockEnd.gif][None.gif]\}

如果每次在我们向ComboBox中添加一项后，就要调用一下这个方法，那就太麻烦了。能不能把这种自适应宽度的功能集成到 ComboBox中呢？这里我们继承ComboBox，实现一个自定义的控件，在用户每次打开下拉列表的时候，让控件自动调整下拉列表的宽度。

1 ![None.gif][] using  System;  
  2 ![None.gif][] using  System.Collections.Generic;  
  3 ![None.gif][] using  System.ComponentModel;  
  4 ![None.gif][] using  System.Drawing;  
  5 ![None.gif][] using  System.Data;  
  6 ![None.gif][] using  System.Text;  
  7 ![None.gif][] using  System.Windows.Forms;  
  8 ![None.gif][]  
  9 ![None.gif][] namespace  WindowsApplication2  
 10 ![ExpandedBlockStart.gif][None.gif]![ContractedBlock.gif][None.gif] ![dot.gif][None.gif] \{  
11![InBlock.gif][None.gif]    class MyComboBox : ComboBox  
12![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]    ![dot.gif][None.gif]\{  
13![InBlock.gif][None.gif]        protected override void OnDropDown(EventArgs e)  
14![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]        ![dot.gif][None.gif]\{  
15![InBlock.gif][None.gif]            base.OnDropDown(e);  
16![InBlock.gif][None.gif]            AdjustComboBoxDropDownListWidth();  //调整comboBox的下拉列表的大小  
17![ExpandedSubBlockEnd.gif][None.gif]        \}  
18![InBlock.gif][None.gif]  
19![InBlock.gif][None.gif]        private void AdjustComboBoxDropDownListWidth()  
20![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]        ![dot.gif][None.gif]\{  
21![InBlock.gif][None.gif]            Graphics g = null;  
22![InBlock.gif][None.gif]            Font font = null;  
23![InBlock.gif][None.gif]            try  
24![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]            ![dot.gif][None.gif]\{  
25![InBlock.gif][None.gif]                int width = this.Width;  
26![InBlock.gif][None.gif]                g = this.CreateGraphics();  
27![InBlock.gif][None.gif]                font = this.Font;  
28![InBlock.gif][None.gif]  
29![InBlock.gif][None.gif]                //checks if a scrollbar will be displayed.  
30![InBlock.gif][None.gif]                //If yes, then get its width to adjust the size of the drop down list.  
31![InBlock.gif][None.gif]                int vertScrollBarWidth =  
32![InBlock.gif][None.gif]                    (this.Items.Count > this.MaxDropDownItems)  
33![InBlock.gif][None.gif]                    ? SystemInformation.VerticalScrollBarWidth : 0;  
34![InBlock.gif][None.gif]  
35![InBlock.gif][None.gif]                int newWidth;  
36![InBlock.gif][None.gif]                foreach (object s in this.Items)  //Loop through list items and check size of each items.  
37![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]                ![dot.gif][None.gif]\{  
38![InBlock.gif][None.gif]                    if (s != null)  
39![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]                    ![dot.gif][None.gif]\{  
40![InBlock.gif][None.gif]                        newWidth = (int)g.MeasureString(s.ToString().Trim(), font).Width  
41![InBlock.gif][None.gif]                            \+ vertScrollBarWidth;  
42![InBlock.gif][None.gif]                        if (width < newWidth)  
43![InBlock.gif][None.gif]                            width = newWidth;   //set the width of the drop down list to the width of the largest item.  
44![ExpandedSubBlockEnd.gif][None.gif]                    \}  
45![ExpandedSubBlockEnd.gif][None.gif]                \}  
46![InBlock.gif][None.gif]                this.DropDownWidth = width;  
47![ExpandedSubBlockEnd.gif][None.gif]            \}  
48![InBlock.gif][None.gif]            catch  
49![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]            ![dot.gif][None.gif]\{ \}  
50![InBlock.gif][None.gif]            finally  
51![ExpandedSubBlockStart.gif][None.gif]![ContractedSubBlock.gif][None.gif]            ![dot.gif][None.gif]\{  
52![InBlock.gif][None.gif]                if (g != null)  
53![InBlock.gif][None.gif]                    g.Dispose();  
54![ExpandedSubBlockEnd.gif][None.gif]            \}  
55![ExpandedSubBlockEnd.gif][None.gif]        \}  
56![ExpandedSubBlockEnd.gif][None.gif]    \}  
57![ExpandedBlockEnd.gif][None.gif]\}

转载于:https://www.cnblogs.com/EthanCai/archive/2008/07/06/1237025.html

[5_1.JPG]: /images/20211220/bb85797e86194c048064f5d139ce8f57.png
[None.gif]: