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

转载：http://blog.sina.com.cn/s/blog_629e606f01014d4b.html

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。

 

void BindComboBox()
{
    flag=false;
    ComboxBox1.ValueMember="ValueColumn";
    ComboxBox1.DisplayMember="DisplayColumn";
    ComboxBox1.DataSource=DataTable1;
    flag=true;
}

 

 

private void 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。

 

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。

 

public partial class frmProduct : Form
    {
DataSet DS = new DataSet();
        String ConnectionString = "integrated security=true; database=AdventureWorks; server=localhost; ";
        public frmProduct()
        {
            InitializeComponent();
        }
       
        private void frmProduct_Load(object sender, EventArgs e)
        {
            SqlDataAdapter da = new SqlDataAdapter("select ProductCategoryID,[Name] from Production.ProductCategory", ConnectionString)
;
            cbbCategories.SelectedIndexChanged -= newEventHandler(cbbCategories_SelectedIndexChanged);
            da.Fill(DS, "ProductCategory");
            cbbCategories.DataSource = null;
            cbbCategories.ValueMember = "ProductCategoryID";          
            cbbCategories.DataSource = DS.Tables["ProductCategory"];
            cbbCategories.SelectedIndexChanged += newEventHandler(cbbCategories_SelectedIndexChanged);
            cbbCategories.DisplayMember = "Name";//这句放在事件委托之后才会有联动效果，下同
        }

        private void 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 -= newEventHandler(cbbSubCategories_SelectedIndexChanged);
            cbbSubCategories.DataSource = null;           
            cbbSubCategories.ValueMember = "ProductSubCategoryID";
            cbbSubCategories.DataSource = DS.Tables["ProductSubCategory"];
            cbbSubCategories.SelectedIndexChanged += newEventHandler(cbbSubCategories_SelectedIndexChanged);
            cbbSubCategories.DisplayMember = "Name";
        }       

        private void 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"];
        }
    }