组合框在DataGridView中没有显示默认值在C＃ [英] Combo box is not displaying default value in DataGridView in C#

问题描述

我试图允许用户从 DataGridViewComboBoxColumn 中为每个新行选择值。我已经绑定 ComboBox 在 GridView 到数据库，但每当我输入新行我看到 DataGridViewComboBoxColumn ，没有初始值。我必须先设置该值。

I'm trying to allow user to select value from DataGridViewComboBoxColumn for each new row. I've bound ComboBox in GridView to database, but whenever I enter new row I see DataGridViewComboBoxColumn with no initial value. I have to set the value first.

每当我在中输入新行时，如何让默认值出现在 DataGridViewComboBoxColumn

How can I let default value appear in DataGridViewComboBoxColumn whenever I enter new row in DataGridView?

这是我绑定 DataGridView ComboBox 到数据库：

This is how I'm binding DataGridView ComboBox to database :

bindingSource1.DataSource = itemBAL.GetTable();
dataGridView1.DataSource = bindingSource1; 
ItemName.DataSource = bindingSource1; //Where ItemName is an instance ofDataGridViewComboBoxColumn
ItemName.DisplayMember = "Name";
ItemName.ValueMember = "ItemId";

推荐答案

您可以使用 DefaultCellStyle .NullValue 和 DefaultCellStyle.DataSourceNullValue 组合框列的属性。

You can use the DefaultCellStyle.NullValue and DefaultCellStyle.DataSourceNullValue properties of the combo box column.

关于此此处的相当全面的MSDN文章。

There is a quite comprehensive MSDN article on this here.

我还给了一个代码示例如下：

I've also given a code example below:

// Let's say I have this list of cars I want to add to my datagridview
List<Car> cars = new List<Car>();
cars.Add(new Car() { Index = 0, Make = "Ford" });
cars.Add(new Car() { Index = 1, Make = "Chevvy" });
cars.Add(new Car() { Index = 2, Make = "Toyota" });

// I create the column, setting all the various properties
DataGridViewComboBoxColumn col = new DataGridViewComboBoxColumn();
col.DataSource = cars;
col.Name = "Cars";
col.DisplayMember = "Make";
col.HeaderText = "Car";
col.ValueMember = "Index";
col.DataPropertyName = "Car";

// As well as standard properties for a combobox column I set these two:
col.DefaultCellStyle.NullValue = cars[0].Make;
col.DefaultCellStyle.DataSourceNullValue = cars[0].Index;

dataGridView1.Columns.Add(col);

dataGridView1.DataSource = dt;

上面的代码需要注意的是，我设置 DataPropertyName 允许与datagridview数据源上的属性绑定。

One thing to note with the code above is that I am setting the DataPropertyName to allow binding with a property on the datagridview's datasource.

如果我不这样做，那么我需要在访问时添加一些额外的逻辑当用户没有选择任何内容时，组合框列，因为属性的值将为null（NullValue不会为实际单元格设置一个值，只显示默认值）。

If I was not doing that then I would need to add some additional logic when accessing the combo box column when users have selected nothing, since the Value of the property would be null (the NullValue does not set a value to the actual cell, only shows a default value).

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