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19.3.3 ComboBox控件与ListBox控件
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19.3.3 ComboBox控件与ListBox控件
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<div style='float:left;width:49%'>·<a href='100165534.htm'>19.3 标准控件和组件</a></div><div style='float:right;width:49%'>·<a href='100165535.htm'>19.3.1 Button控件</a></div><div style='float:left;width:49%'>·<a href='100165536.htm'>19.3.2 CheckBox控件</a></div><div style='float:right;width:49%'>·<a href='100165538.htm'>19.3.4 DateTimePicker控件</a></div><div style='float:left;width:49%'>·<a href='100165539.htm'>19.3.5 ErrorProvider组件</a></div><div style='float:right;width:49%'>·<a href='100165540.htm'>19.3.6 HelpProvider组件</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><span lang="EN-US">19.3.3 ComboBox</span><span style="FONT-FAMILY: 黑体">控件与</span><span lang="EN-US">ListBox</span><span style="FONT-FAMILY: 黑体">控件</span></h3>
<p class="MsoNormal"><span lang="EN-US">ComboBox</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">ListBox</span><span style="FONT-FAMILY: 宋体">都派生于</span><span lang="EN-US">ListControl</span><span style="FONT-FAMILY: 宋体">类。这个类提供了一些基本的列表管理功能。</span><span lang="EN-US">SelectedIndex</span><span style="FONT-FAMILY: 宋体">返回一个整数值，它对应于当前选中项目的索引。从列表中获取值有点困难，在给列表控件添加条目时，不仅可以添加字符串值，还可以添加任意类型的对象。如果要添加的条目不是字符串，就必须设置另外两个属性。第一个是</span><span lang="EN-US">DisplayMember</span><span style="FONT-FAMILY: 宋体">属性，这个设置告诉</span><span lang="EN-US">ListControl</span><span style="FONT-FAMILY: 宋体">在列表中显示对象的哪个属性。另一个是</span><span lang="EN-US">ValueMember</span><span style="FONT-FAMILY: 宋体">属性，它是要返回值的对象属性。例如，如果要使用</span><span lang="EN-US">Country</span><span style="FONT-FAMILY: 宋体">对象，它包含两个属性</span><span lang="EN-US">CountryName</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">CountryAbbreviation</span><span style="FONT-FAMILY: 宋体">，就应把</span><span lang="EN-US">DisplayMember</span><span style="FONT-FAMILY: 宋体">设置为</span><span lang="EN-US">CountryName</span><span style="FONT-FAMILY: 宋体">属性，把</span><span lang="EN-US">ValueMember</span><span style="FONT-FAMILY: 宋体">设置为</span><span lang="EN-US">CountryAbbreviation</span><span style="FONT-FAMILY: 宋体">。在显示列表时，就会看到国家名称的列表，在使用</span><span lang="EN-US">SelectedValue</span><span style="FONT-FAMILY: 宋体">属性时，控件应返回列表中所选中国家的简称。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果访问</span><span lang="EN-US">Items</span><span style="FONT-FAMILY: 宋体">属性，就可以得到</span><span lang="EN-US">Country</span><span style="FONT-FAMILY: 宋体">对象。</span><span lang="EN-US">Items</span><span style="FONT-FAMILY: 宋体">属性在控件上执行。在</span><span lang="EN-US">ListBox</span><span style="FONT-FAMILY: 宋体">控件上，</span><span lang="EN-US">Items</span><span style="FONT-FAMILY: 宋体">属性返回</span><span lang="EN-US">ListBox.ObjectCollection</span><span style="FONT-FAMILY: 宋体">。这是一个可以通过索引器引用的对象集合。所以，要获取对象</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">不是</span><span lang="EN-US">ValueMember</span><span style="FONT-FAMILY: 宋体">，而是对象本身</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，就可以使用下面的代码：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">obj = listBox1.Items[listBox1. SelectedIndex];</span></p>
<p class="MsoNormal"><span lang="EN-US">ComboBox</span><span style="FONT-FAMILY: 宋体">的</span><span lang="EN-US">Items</span><span style="FONT-FAMILY: 宋体">属性返回</span><span lang="EN-US">ComboBox.ObjectCollection</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">ComboBox</span><span style="FONT-FAMILY: 宋体">组合了编辑控件和列表框。通过把一个</span><span lang="EN-US">DropDownStyle</span><span style="FONT-FAMILY: 宋体">枚举值传送给</span><span lang="EN-US">DropDownStyle</span><span style="FONT-FAMILY: 宋体">属性，就可以设置</span><span lang="EN-US">ComboBox</span><span style="FONT-FAMILY: 宋体">的样式。表</span><span lang="EN-US">19-2</span><span style="FONT-FAMILY: 宋体">列出了</span><span lang="EN-US">DropDownStyle</span><span style="FONT-FAMILY: 宋体">的各个值。</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="a5" style="MARGIN-TOP: 8.15pt"><span style="FONT-FAMILY: 黑体">表</span><span lang="EN-US"> 19-2</span></p>
<table class="MsoNormalTable" style="BORDER-TOP-STYLE: none; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none; BORDER-COLLAPSE: collapse; BORDER-BOTTOM-STYLE: none" cellspacing="0" cellpadding="0" border="1">
<tbody>
<tr>
<td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; PADDING-LEFT: 5.4pt; BORDER-LEFT-WIDTH: 1pt; BORDER-LEFT-COLOR: windowtext; PADDING-BOTTOM: 0cm; WIDTH: 76.3pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid" valign="top" width="102">
<p class="a2"><span style="FONT-FAMILY: 黑体">值</span></p>
</td>
<td style="PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 365.35pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none" valign="top" width="487">
<p class="a2"><span style="FONT-FAMILY: 黑体">说</span><span lang="EN-US"> </span><span style="FONT-FAMILY: 黑体">明</span></p>
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<tr>
<td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 76.3pt; BORDER-TOP-STYLE: none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT-STYLE: none" valign="top" width="102">
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">DropDown</span></p>
</td>
<td style="PADDING-RIGHT: 5.4pt; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 365.35pt; BORDER-TOP-STYLE: none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none" valign="top" width="487">
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">组合框的文本部分是可以编辑的，用户可以输入值。用户必须单击箭头按钮，才能显示列表</span></p>
</td>
</tr>
<tr>
<td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 76.3pt; BORDER-TOP-STYLE: none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT-STYLE: none" valign="top" width="102">
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">DropDownList</span></p>
</td>
<td style="PADDING-RIGHT: 5.4pt; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 365.35pt; BORDER-TOP-STYLE: none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none" valign="top" width="487">
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">文本部分不能编辑。用户必须从列表中选择</span></p>
</td>
</tr>
<tr>
<td style="BORDER-RIGHT: windowtext 1pt solid; PADDING-RIGHT: 5.4pt; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 76.3pt; BORDER-TOP-STYLE: none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT-STYLE: none" valign="top" width="102">
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span lang="EN-US">Simple</span></p>
</td>
<td style="PADDING-RIGHT: 5.4pt; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; WIDTH: 365.35pt; BORDER-TOP-STYLE: none; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 1pt solid; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none" valign="top" width="487">
<p class="a4" style="MARGIN-LEFT: 10.7pt"><span style="FONT-FAMILY: 宋体">类似于</span><span lang="EN-US">DropDown</span><span style="FONT-FAMILY: 宋体">，但列表总是可见的</span></p>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果列表中的值比较宽，就可以使用</span><span lang="EN-US">DropDownWidth</span><span style="FONT-FAMILY: 宋体">属性改变控件下拉部分的宽度。</span><span lang="EN-US">MaxDropDownItems</span><span style="FONT-FAMILY: 宋体">属性设置在显示列表的下拉部分时的最大项目数。</span></p>
<p class="MsoNormal"><span lang="EN-US">FindString</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">FindStringExact</span><span style="FONT-FAMILY: 宋体">方法是列表控件的另外两个有用的方法。</span><span lang="EN-US">FindString</span><span style="FONT-FAMILY: 宋体">在列表中查找以传入字符串开头的第一个字符串。</span><span lang="EN-US">FindStringExact</span><span style="FONT-FAMILY: 宋体">查找与传入字符串匹配的第一个字符串。它们都返回找到的值的索引，如果没有找到，就返回–</span><span lang="EN-US">1</span><span style="FONT-FAMILY: 宋体">。它们还可以将要搜索的起始索引整数作为参数。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在列表控件中，最常用的事件是</span><span lang="EN-US">SelectedIndexChanged</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">SelectedValueChanged</span><span style="FONT-FAMILY: 宋体">。这些事件是在用户从列表中选择新条目时发生。在列表中选择了新条目后，就可以修改窗体的其他方面，以匹配新选中的条目。例如，使用</span><span lang="EN-US">Country</span><span style="FONT-FAMILY: 宋体">列表，如果用户从列表中选择了一个新国家，就可以显示该国家的地图图像。</span></p></div>
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<h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165537.htm'><font color='red'>19.3.3 ComboBox控件与ListBox控件</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100165534.htm'>19.3 标准控件和组件</a></div><div style='float:right;width:49%'>·<a href='100165535.htm'>19.3.1 Button控件</a></div><div style='float:left;width:49%'>·<a href='100165536.htm'>19.3.2 CheckBox控件</a></div><div style='float:right;width:49%'>·<a href='100165538.htm'>19.3.4 DateTimePicker控件</a></div><div style='float:left;width:49%'>·<a href='100165539.htm'>19.3.5 ErrorProvider组件</a></div><div style='float:right;width:49%'>·<a href='100165540.htm'>19.3.6 HelpProvider组件</a></div></div>
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