WPF,ComboBox,取汉字首字母，extBoxBase.TextChanged

1取汉字汉语拼音首字母：

private static string GetFirstLetterOfChineseString(string CnChar)
{
long iCnChar;
byte[] ZW = System.Text.Encoding.Default.GetBytes(CnChar);

//如果是字母，则直接返回
if (ZW.Length == 1)
{
return CnChar.ToUpper();
}
else
{
int i1 = (short)(ZW[0]);
int i2 = (short)(ZW[1]);
iCnChar = i1 * 256 + i2;
}
if ((iCnChar >= 45217) && (iCnChar <= 45252))
{
return "A";
}
else if ((iCnChar >= 45253) && (iCnChar <= 45760))
{
return "B";
}
else if ((iCnChar >= 45761) && (iCnChar <= 46317))
{
return "C";
}
else if ((iCnChar >= 46318) && (iCnChar <= 46825))
{
return "D";
}
else if ((iCnChar >= 46826) && (iCnChar <= 47009))
{
return "E";
}
else if ((iCnChar >= 47010) && (iCnChar <= 47296))
{
return "F";
}
else if ((iCnChar >= 47297) && (iCnChar <= 47613))
{
return "G";
}
else if ((iCnChar >= 47614) && (iCnChar <= 48118))
{
return "H";
}
else if ((iCnChar >= 48119) && (iCnChar <= 49061))
{
return "J";
}
else if ((iCnChar >= 49062) && (iCnChar <= 49323))
{
return "K";
}
else if ((iCnChar >= 49324) && (iCnChar <= 49895))
{
return "L";
}
else if ((iCnChar >= 49896) && (iCnChar <= 50370))
{
return "M";
}

else if ((iCnChar >= 50371) && (iCnChar <= 50613))
{
return "N";
}
else if ((iCnChar >= 50614) && (iCnChar <= 50621))
{
return "O";
}
else if ((iCnChar >= 50622) && (iCnChar <= 50905))
{
return "P";
}
else if ((iCnChar >= 50906) && (iCnChar <= 51386))
{
return "Q";
}
else if ((iCnChar >= 51387) && (iCnChar <= 51445))
{
return "R";
}
else if ((iCnChar >= 51446) && (iCnChar <= 52217))
{
return "S";
}
else if ((iCnChar >= 52218) && (iCnChar <= 52697))
{
return "T";
}
else if ((iCnChar >= 52698) && (iCnChar <= 52979))
{
return "W";
}
else if ((iCnChar >= 52980) && (iCnChar <= 53640))
{
return "X";
}
else if ((iCnChar >= 53689) && (iCnChar <= 54480))
{
return "Y";
}
else if ((iCnChar >= 54481) && (iCnChar <= 55289))
{
return "Z";
}
else return ("?");
}

2.ComboBox TextChanged事件  TextBoxBase.TextChanged="Cmb_OnTextChanged"

<ComboBox x:Name="cmb" Grid.Row="0" Grid.Column="0" IsEditable="True" IsTextSearchCaseSensitive="False" IsTextSearchEnabled="True" FontSize="30"    TextBoxBase.TextChanged="Cmb_OnTextChanged">

3. 文字变化，过滤下拉框，下拉框弹出

private void Cmb_OnTextChanged(object sender, TextChangedEventArgs e)
{
filterList = new List<string>();
string str = cmb.Text;
if (string.IsNullOrEmpty(str.Trim()))
{
cmb.ItemsSource = null;
cmb.Items.Clear();
cmb.ItemsSource = list;
cmb.IsDropDownOpen = true;
return;
}

foreach (var l in list)
{
cmb.ItemsSource = null;
cmb.Items.Clear();
if (GetFirstLetterOfChineseString(l).ToLower().Equals(str.Trim()))
{
if (!filterList.Contains(l))
{
filterList.Add(l);
}
}
cmb.ItemsSource = filterList;
cmb.IsDropDownOpen = true;
}
}