Question

我将我的组合框绑定到数据库，我可以从我的数据库中填充组合框。但是当我打开页面时，组合框默认包含一个值来自数据库。我想在我的组合框中显示空白，怎么做？

my code:

datatable dt;

DataAccess.Connect();
            dt = DataAccess.Select("select * from CompanyMainActivity");
            cmbMainActivity.DisplayMember = ("name");
            cmbMainActivity.ValueMember = "MainActivityCode";
            cmbMainActivity.DataSource = dt;

我尝试使用此代码，但需要付出代价

cmbMainActivity.Items.Insert（0，＆＃34;从CompanyMainActivity＆＃34中选择名称;）;

Answer 1

您可以在第一个时添加空白值。

dt = DataAccess.Select("select name, MainActivityCode from CompanyMainActivity");

//Insert default row
DataRow dr = dt.NewRow();
dr["name"] = String.Empty;
dr["MainActivityCode"] = -1; //I have set -1 because it should not be duplicate and this record is fake. so, we can determine that the record is fake from the -1 value.
dt.Rows.InsertAt(dr, 0); //Insert the blank record at the top of the all records.

cmbMainActivity.DisplayMember = ("name");
cmbMainActivity.ValueMember = "MainActivityCode";
cmbMainActivity.DataSource = dt;

Answer 2

我想你要找的东西叫做占位符。请参考这些可能有用的链接。

[Combo box's different properties][1](http://www.dotnetperls.com/combobox)
[If u r using wpf controls][2](http://pwlodek.blogspot.in/2009/11/watermark-effect-for-wpfs-textbox.html)
[check this also][3](http://msdn.microsoft.com/en-us/library/windows/apps/bg182878.aspx)

Answer 3

假设您正在使用WPF

在xaml文件的组合框部分添加SelectedIndex

<ComboBox>
   ...
   SelectedIndex = -1
   ...
</ComboBox>

在combobox中显示空白绑定到数据库

3 个答案: