使用特定条件筛选数据，然后通过 UI 控件将数据呈现给客户端的功能是数据绑定的一个重要方面。 DataView 提供了多种方法来筛选数据并返回满足特定筛选条件的数据行子集。 除了基于字符串的筛选功能外， DataView 还提供将 LINQ 表达式用于筛选条件的功能。 LINQ 表达式允许比基于字符串的筛选更复杂、更强大的筛选作。
使用 DataView 筛选数据的方法有两种：
通过具有筛选信息的查询创建 DataView
可以从 LINQ to DataSet 查询创建一个DataView对象。 如果该查询包含 Where 从句，则会使用查询中的筛选信息创建 DataView。 Where 子句中的表达式用于确定哪些数据行将包括在 DataView 中并作为筛选器的基础。
基于表达式的筛选器比基于字符串的简单筛选器提供更强大的复杂筛选功能。 基于字符串的筛选器和基于表达式的筛选器是互斥的。 当从查询创建 RowFilter 后设置基于字符串的 DataView 时，会清除从查询推断的基于表达式的筛选器。
注释
在大多数情况下，用于筛选的表达式不应具有副作用，并且必须具有确定性。 此外，表达式不应包含依赖于一组执行数的任何逻辑，因为筛选作可能会执行任意次数。
示例：
以下示例查询 SalesOrderDetail 表以获取数量大于 2 且小于 6 的订单，从该查询创建一个DataView，并将DataView绑定到BindingSource。
DataTable orders = _dataSet.Tables["SalesOrderDetail"];
EnumerableRowCollection<DataRow> query = from order in orders.AsEnumerable()
where order.Field<short>("OrderQty") > 2 && order.Field<short>("OrderQty") < 6
select order;
DataView view = query.AsDataView();
bindingSource1.DataSource = view;
Dim orders As DataTable = dataSet.Tables("SalesOrderDetail")
Dim query = _
From order In orders.AsEnumerable() _
Where order.Field(Of Int16)("OrderQty") > 2 And _
order.Field(Of Int16)("OrderQty") < 6 _
Select order
Dim view As DataView = query.AsDataView()
bindingSource1.DataSource = view
示例：
以下示例从查询中生成一个 DataView，该查询用于查找在 2001 年 6 月 6 日之后下的订单：
DataTable orders = _dataSet.Tables["SalesOrderHeader"];
EnumerableRowCollection<DataRow> query = from order in orders.AsEnumerable()
where order.Field<DateTime>("OrderDate") > new DateTime(2002, 6, 1)
select order;
DataView view = query.AsDataView();
bindingSource1.DataSource = view;
Dim orders As DataTable = dataSet.Tables("SalesOrderHeader")
Dim query = _
From order In orders.AsEnumerable() _
Where order.Field(Of DateTime)("OrderDate") > New DateTime(2002, 6, 1) _
Select order
Dim view As DataView = query.AsDataView()
bindingSource1.DataSource = view
示例：
还可以将筛选与排序相结合。 下面的示例通过查询姓氏以“S”开始并按姓氏排序，然后按名字排序的联系人来创建 DataView：
DataTable contacts = _dataSet.Tables["Contact"];
EnumerableRowCollection<DataRow> query = from contact in contacts.AsEnumerable()
where contact.Field<string>("LastName").StartsWith("S")
orderby contact.Field<string>("LastName"), contact.Field<string>("FirstName")
select contact;
DataView view = query.AsDataView();
bindingSource1.DataSource = view;
dataGridView1.AutoResizeColumns();
Dim contacts As DataTable = dataSet.Tables("Contact")
Dim query = _
From contact In contacts.AsEnumerable() _
Where contact.Field(Of String)("LastName").StartsWith("S") _
Order By contact.Field(Of String)("LastName"), contact.Field(Of String)("FirstName") _
Select contact
Dim view As DataView = query.AsDataView()
bindingSource1.DataSource = view
dataGridView1.AutoResizeColumns()
示例：
以下示例使用 SoundEx 算法查找姓氏类似于“Zhu”的联系人。 SoundEx 算法在 SoundEx 方法中实现。
DataTable contacts = _dataSet.Tables["Contact"];
var soundExCode = SoundEx("Zhu");
EnumerableRowCollection<DataRow> query = from contact in contacts.AsEnumerable()
where SoundEx(contact.Field<string>("LastName")) == soundExCode
select contact;
DataView view = query.AsDataView();
bindingSource1.DataSource = view;
dataGridView1.AutoResizeColumns();
Dim contacts As DataTable = dataSet.Tables("Contact")
Dim soundExCode As String = SoundEx("Zhu")
Dim query = _
From contact In contacts.AsEnumerable() _
Where SoundEx(contact.Field(Of String)("LastName")) = soundExCode _
Select contact
Dim view As DataView = query.AsDataView()
bindingSource1.DataSource = view
dataGridView1.AutoResizeColumns()
SoundEx 是一种拼音算法，用于按声音为名称编制索引，因为它们用英语发音，最初由美国人口普查局开发。 SoundEx 方法返回一个名称的四个字符代码，该代码由英文字母后跟三个数字组成。 字母是名称的第一个字母，数字在名称中对剩余的同音进行编码。 发音相似的名称共享相同的 SoundEx 编码。 以下示例的 SoundEx 方法中使用的 SoundEx 实现如下所示：
static string SoundEx(string word)
{
// The length of the returned code.
const int length = 4;
// Value to return.
var value = "";
// The size of the word to process.
var size = word.Length;
// The word must be at least two characters in length.
if (size > 1)
{
// Convert the word to uppercase characters.
word = word.ToUpper(CultureInfo.InvariantCulture);
// Convert the word to a character array.
var chars = word.ToCharArray();
// Buffer to hold the character codes.
var buffer = new StringBuilder
{
Length = 0
};
// The current and previous character codes.
var prevCode = 0;
var currCode = 0;
// Add the first character to the buffer.
buffer.Append(chars[0]);
// Loop through all the characters and convert them to the proper character code.
for (var i = 1; i < size; i++)
{
switch (chars[i])
{
case 'A':
case 'E':
case 'I':
case 'O':
case 'U':
case 'H':
case 'W':
case 'Y':
currCode = 0;
break;
case 'B':
case 'F':
case 'P':
case 'V':
currCode = 1;
break;
case 'C':
case 'G':
case 'J':
case 'K':
case 'Q':
case 'S':
case 'X':
case 'Z':
currCode = 2;
break;
case 'D':
case 'T':
currCode = 3;
break;
case 'L':
currCode = 4;
break;
case 'M':
case 'N':
currCode = 5;
break;
case 'R':
currCode = 6;
break;
}
// Check if the current code is the same as the previous code.
if (currCode != prevCode)
{
// Check to see if the current code is 0 (a vowel); do not process vowels.
if (currCode != 0)
{
buffer.Append(currCode);
}
}
// Set the previous character code.
prevCode = currCode;
// If the buffer size meets the length limit, exit the loop.
if (buffer.Length == length)
{
break;
}
}
// Pad the buffer, if required.
size = buffer.Length;
if (size < length)
{
buffer.Append('0', length - size);
}
// Set the value to return.
value = buffer.ToString();
}
// Return the value.
return value;
}
Private Function SoundEx(ByVal word As String) As String
Dim length As Integer = 4
' Value to return
Dim value As String = ""
' Size of the word to process
Dim size As Integer = word.Length
' Make sure the word is at least two characters in length
If (size > 1) Then
' Convert the word to all uppercase
word = word.ToUpper(System.Globalization.CultureInfo.InvariantCulture)
' Convert the word to character array for faster processing
Dim chars As Char() = word.ToCharArray()
' Buffer to build up with character codes
Dim buffer As StringBuilder = New StringBuilder()
' The current and previous character codes
Dim prevCode As Integer = 0
Dim currCode As Integer = 0
' Append the first character to the buffer
buffer.Append(chars(0))
' Loop through all the characters and convert them to the proper character code
For i As Integer = 1 To size - 1
Select Case chars(i)
Case "A", "E", "I", "O", "U", "H", "W", "Y"
currCode = 0
Case "B", "F", "P", "V"
currCode = 1
Case "C", "G", "J", "K", "Q", "S", "X", "Z"
currCode = 2
Case "D", "T"
currCode = 3
Case "L"
currCode = 4
Case "M", "N"
currCode = 5
Case "R"
currCode = 6
End Select
' Check to see if the current code is the same as the last one
If (currCode <> prevCode) Then
' Check to see if the current code is 0 (a vowel); do not process vowels
If (currCode <> 0) Then
buffer.Append(currCode)
End If
End If
' Set the new previous character code
prevCode = currCode
' If the buffer size meets the length limit, then exit the loop
If (buffer.Length = length) Then
Exit For
End If
Next
' Pad the buffer, if required
size = buffer.Length
If (size < length) Then
buffer.Append("0", (length - size))
End If
' Set the value to return
value = buffer.ToString()
End If
' Return the value
Return value
End Function
使用 RowFilter 属性
LINQ to DataSet 上下文中的现有基于字符串的 DataView 筛选功能仍然有效。 有关基于 RowFilter 字符串的筛选的详细信息，请参阅 “排序和筛选数据”。
以下示例从 Contact 表创建一个 DataView ，然后设置属性 RowFilter 以返回联系人姓氏为“Zhu”的行：
DataTable contacts = _dataSet.Tables["Contact"];
DataView view = contacts.AsDataView();
view.RowFilter = "LastName='Zhu'";
bindingSource1.DataSource = view;
dataGridView1.AutoResizeColumns();
Dim contacts As DataTable = dataSet.Tables("Contact")
Dim view As DataView = contacts.AsDataView()
view.RowFilter = "LastName='Zhu'"
bindingSource1.DataSource = view
dataGridView1.AutoResizeColumns()
从DataView或LINQ to DataSet查询中创建DataTable后，可以使用RowFilter属性根据行的列值指定行的子集。 基于字符串的筛选器和基于表达式的筛选器是互斥的。 设置该 RowFilter 属性将清除从 LINQ to DataSet 查询推断出的筛选器表达式，并且无法重置筛选器表达式。
DataTable contacts = _dataSet.Tables["Contact"];
EnumerableRowCollection<DataRow> query = from contact in contacts.AsEnumerable()
where contact.Field<string>("LastName") == "Hernandez"
select contact;
DataView view = query.AsDataView();
bindingSource1.DataSource = view;
dataGridView1.AutoResizeColumns();
view.RowFilter = "LastName='Zhu'";
Dim contacts As DataTable = dataSet.Tables("Contact")
Dim query = _
From contact In contacts.AsEnumerable() _
Where contact.Field(Of String)("LastName") = "Hernandez" _
Select contact
Dim view As DataView = query.AsDataView()
bindingSource1.DataSource = view
dataGridView1.AutoResizeColumns()
view.RowFilter = "LastName='Zhu'"
如果要返回对数据的特定查询的结果，而不是提供数据子集的动态视图，则可以使用 Find 或 FindRows 方法 DataView，而不是设置 RowFilter 属性。 该 RowFilter 属性最适用于数据绑定应用程序中，其中绑定控件显示筛选的结果。 RowFilter设置属性会重新生成数据的索引，从而增加应用程序开销并降低性能。 和FindFindRows方法使用当前索引，而无需重新生成索引。 如果只调用一次Find或FindRows，则应使用现有的DataView。 如果要调用 Find 或 FindRows 多次调用，则应创建一个新 DataView 方法来重新生成要搜索的列上的索引，然后调用 Find 或 FindRows 方法。 有关Find和FindRows方法的更多信息，请参阅查找行和DataView 性能。
清除筛选器
使用 DataView 属性设置筛选后，可以清除 RowFilter 上的筛选器。 可以通过两种不同的方式清除一个 DataView 上的筛选器：
示例：
以下示例从查询创建一个DataView，然后通过将RowFilter属性设置为null来清除筛选器：
DataTable orders = _dataSet.Tables["SalesOrderHeader"];
EnumerableRowCollection<DataRow> query = from order in orders.AsEnumerable()
where order.Field<DateTime>("OrderDate") > new DateTime(2002, 11, 20)
&& order.Field<decimal>("TotalDue") < new decimal(60.00)
select order;
DataView view = query.AsDataView();
bindingSource1.DataSource = view;
view.RowFilter = null;
Dim orders As DataTable = dataSet.Tables("SalesOrderHeader")
Dim query = _
From order In orders.AsEnumerable() _
Where order.Field(Of DateTime)("OrderDate") > New DateTime(2002, 11, 20) _
And order.Field(Of Decimal)("TotalDue") < New Decimal(60.0) _
Select order
Dim view As DataView = query.AsDataView()
bindingSource1.DataSource = view
view.RowFilter = Nothing
示例：
以下示例从表创建一个 DataView，设置 RowFilter 属性，然后通过将 RowFilter 属性设置为空字符串来清除筛选器：
DataTable contacts = _dataSet.Tables["Contact"];
DataView view = contacts.AsDataView();
view.RowFilter = "LastName='Zhu'";
bindingSource1.DataSource = view;
dataGridView1.AutoResizeColumns();
// Clear the row filter.
view.RowFilter = "";
Dim contacts As DataTable = dataSet.Tables("Contact")
Dim view As DataView = contacts.AsDataView()
view.RowFilter = "LastName='Zhu'"
bindingSource1.DataSource = view
dataGridView1.AutoResizeColumns()
' Clear the row filter.
view.RowFilter = ""