ComboBox绑定数据源时触发SelectedIndexChanged事件的处理办法

转载；http://hi.baidu.com/haoyun2012/item/d780ca157a29b239b9318080 感谢原作者

ComboBox最经常使用的事件就是SelectedIndexChanged。但在将ComboBox绑定到某个数据源的过程中，会触发SelectedIndexChanged

事件，而这个时候用户并没有选择内容，其SelectedValue也不是对应字段的值。那么时写在SelectedIndexChanged中的处理代码就会因为SelectedValue的内容不正确引发异常。

一般网上找到的方法是添加一个标记位，在绑定前设置为false，绑定完成后设置回true。




绑定到ComboBoxvoid BindComboBox()

{

flag=false;

ComboxBox1.ValueMember="ValueColumn";

ComboxBox1.DisplayMember="DisplayColumn";

ComboxBox1.DataSource=DataTable1;

flag=true;

}



事件处理privatevoid ComboxBox1_SelectedIndexChanged(object sender, EventArgs e)

{

if(flag)

{

//Do something

}

}
另外还有一种办法，就是在绑定前，将SelectedIndexChanged的委托去掉，等绑定完成后，再添加事件委托。




增减委托绑定void BindComboBox()

{ //去除委托

ComboBox1.SelectedIndexChanged -=new EventHandler(ComboBox1_SelectedIndexChanged);

ComboBox1.DataSource =null;

ComboBox1.ValueMember ="ValueColumn";

ComboBox1.DataSource = DataTable1;

//添加委托

ComboBox1.SelectedIndexChanged +=new EventHandler(ComboBox1_SelectedIndexChanged);

ComboBox1.DisplayMember ="DisplayColumn";

}

两种方法都可以，但是之间的优劣暂时没去比较。感觉好像处理一下委托会好点。因为这种办法真的减少了事件的激发次数。

不知道还有没有其他解决方案呢？

另，贴上一段完整的代码例子。这个例子是访问SqlServer数据库的AdventureWorks，通过ProductCategory和ProductSubCategory两级目录分类去查看Product表的内容。分别使用两个ComboBox和DataGridView完成数据绑定。效果就是选择之后会联动改变相关内容。




二级选择框联动显示数据publicpartialclass frmProduct : Form

{

DataSet DS =new DataSet();

String ConnectionString ="integrated security=true; database=AdventureWorks; server=localhost; ";

public frmProduct()

{

InitializeComponent();

}

privatevoid frmProduct_Load(object sender, EventArgs e)

{

SqlDataAdapter da =new SqlDataAdapter("select ProductCategoryID,[Name] from Production.ProductCategory", ConnectionString)

;

cbbCategories.SelectedIndexChanged -=new EventHandler(cbbCategories_SelectedIndexChanged);

da.Fill(DS, "ProductCategory");

cbbCategories.DataSource =null;

cbbCategories.ValueMember ="ProductCategoryID";

cbbCategories.DataSource = DS.Tables["ProductCategory"];

cbbCategories.SelectedIndexChanged +=new EventHandler(cbbCategories_SelectedIndexChanged);

cbbCategories.DisplayMember ="Name";//这句放在事件委托之后才会有联动效果，下同

}

privatevoid cbbCategories_SelectedIndexChanged(object sender, EventArgs e)

{

SqlDataAdapter da =new SqlDataAdapter("select ProductSubCategoryID,[Name] from Production.ProductSubCategory where ProductCategoryID="+ cbbCategories.SelectedValue.ToString(), ConnectionString)

;

if (DS.Tables["ProductSubCategory"] !=null)

{

DS.Tables["ProductSubCategory"].Clear();

}

da.Fill(DS, "ProductSubCategory");

cbbSubCategories.SelectedIndexChanged -=new EventHandler(cbbSubCategories_SelectedIndexChanged);

cbbSubCategories.DataSource =null;

cbbSubCategories.ValueMember ="ProductSubCategoryID";

cbbSubCategories.DataSource = DS.Tables["ProductSubCategory"];

cbbSubCategories.SelectedIndexChanged +=new EventHandler(cbbSubCategories_SelectedIndexChanged);

cbbSubCategories.DisplayMember ="Name";

}

privatevoid cbbSubCategories_SelectedIndexChanged(object sender, EventArgs e)

{

if (cbbSubCategories.SelectedIndex ==-1)

return;

SqlDataAdapter da=new SqlDataAdapter("select * from Production.Product where ProductSubCategoryID="+ cbbSubCategories.SelectedValue.ToString(), ConnectionString);

dgvProduct.DataSource =null;

if (DS.Tables["Product"] !=null)

DS.Tables["Product"].Clear();

da.Fill(DS, "Product");

dgvProduct.DataSource = DS.Tables["Product"];

}

}