【发布时间】：2015-10-19 16:52:09
【问题描述】：
我有三个组合框。我从数据库中获取每个组合框的值，每个组合框都依赖于另一个。目前，我正在填充 SelectionChanged() 事件的组合框。 我在 MainWindow 的构造函数中填充第一个组合框。
因此，当我从第一个组合框中选择一个值时，将调用 selectionchanged 事件。然后填充第二个组合框。当我从第二个组合框中选择一个值时，第三个组合框会在 selectionChanged 事件中填充。从第三个组合框中选择值后，我正在填充数据网格。
当我从第三个组合框选择值后尝试更改第一个组合框的值时，出现错误。
对象引用未设置为对象的实例！
我正在尝试将组合框相互绑定，但对于 wpf 来说，我想不出一种方法来做到这一点。
我附上了组合框的代码供参考。
public MainWindow()
{
InitializeComponent();
Fill_Combo();
}
//adding values in first combo box
void Fill_Combo()
{
try
{
string query = "select column_name from table_name";
if (conn.State == ConnectionState.Closed)
{
conn.Open();
}
OracleCommand command = new OracleCommand();
command.Connection = conn;
command.CommandText = query;
OracleDataReader reader = command.ExecuteReader();
while (reader.Read())
{
String str = reader.GetString(0);
//source_name is name of combobox1
source_name.Items.Add(str);
}
reader.Dispose();
}
catch (Exception e)
{
MessageBox.Show(e.StackTrace + " :: in fill_combo");
}
}
// adding value in second combo box based on value in first combobox
private void source_name_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
string query = "select column from table where source_name='" + source_name.SelectedItem.ToString() + "'";
try
{
OracleConnection connection = new OracleConnection(connectionString);
connection.Open();
OracleCommand command = new OracleCommand();
command.Connection = connection;
command.CommandText = query;
OracleDataReader reader = command.ExecuteReader();
//clearing previous values in combobox2
//target_box is the name of second combo box
target_box.Items.Clear();
while (reader.Read())
{
String str = reader.GetString(0);
//adding values in second combobox
target_box.Items.Add(str);
}
reader.Dispose();
connection.Close();
}
catch (Exception exp)
{
MessageBox.Show(exp.Message + "source_name namespace SelectionChangedEventArgs chanegs");
}
}
private void target_box_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
try
{
if (target_box.SelectedItem.ToString() != null && target_box.SelectedItem.ToString() != "Target system")
{
string query = "select columnname from map_pair_attributes where source_name='" + source_name.SelectedItem.ToString() + "'"
+ "and target_name = '" + target_box.SelectedItem.ToString() + "'";
OracleConnection connection = new OracleConnection(connectionString);
connection.Open();
OracleCommand command = new OracleCommand();
command.Connection = connection;
command.CommandText = query;
OracleDataReader reader = command.ExecuteReader();
attribute_box.Items.Clear();
while (reader.Read())
{
String str = reader.GetString(0);
//attribute box is name of third combobox
attribute_box.Items.Add(str);
}
reader.Dispose();
connection.Close();
connection.Dispose();
}
}
catch (Exception ex)
{
MessageBox.Show("in target box selection changed!" + ex.StackTrace + ex.Message);
}
}
//atributebox is name of third combobox
private void attribute_box_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
try
{
String query = "select column_name from table where source_name='" + source_name.SelectedItem.ToString() + "' and target_name ='" +
target_box.SelectedItem.ToString() + "' and attribute_name = '" + attribute_box.SelectedItem.ToString() + "'";
OracleConnection conn = new OracleConnection(connectionString);
conn.Open();
DataSet ds = new DataSet();
OracleDataAdapter da = new OracleDataAdapter(query, conn);
da.Fill(ds, "table_name");
grid1.ItemsSource = ds.Tables["table_name"].DefaultView;
conn.Close();
}
catch (Exception ex)
{
MessageBox.Show("attribute box selection changed!" + ex.Message);
}
}
.XAML 文件
<ComboBox x:Name="target_box" HorizontalAlignment="Left" Margin="179,49,0,0" VerticalAlignment="Top" Width="120"
IsEditable="true" IsReadOnly="True" Text="Target system"
Focusable="True" SelectionChanged="target_box_SelectionChanged" />
<ComboBox x:Name="source_name" HorizontalAlignment="Left" Margin="19,49,0,0" VerticalAlignment="Top" Width="120"
IsEditable="true" IsReadOnly="True" Text="Source system" Focusable="True" SelectionChanged="source_name_SelectionChanged"/>
<ComboBox x:Name="attribute_box" HorizontalAlignment="Left" Margin="363,49,0,0" VerticalAlignment="Top" Width="120"
IsEditable="true" IsReadOnly="True" Text="Attribute" Focusable="True" SelectionChanged="attribute_box_SelectionChanged" />
有人可以帮我解决这个问题吗？ 我认为绑定可以解决问题，但我不知道如何绑定组合框。
谢谢！
【问题讨论】：
-
互联网上关于 WPF 数据绑定的信息和示例数不胜数。在发布此类问题之前，您应该进行一些研究。
-
我找到了一些示例并实现了它，但我找到了绑定单个组合框的示例。我在绑定多个组合框方面没有找到太多帮助。我现在被这个问题困扰了很多天。我还在网上搜索这个。正如我在问题中已经提到的那样，我是 WPF 的新手，对绑定也不太了解。不过还是谢谢！
-
您可以将两个 ComboBox 绑定到同一个源属性
标签： c# wpf winforms xaml combobox