见以下示例
using System;using SystemCollectionsGeneric;
using SystemLinq;
namespace MyApplication
{
class Program
{
public class MyClass
{
public string Name { get; set; }
public bool IsTrue { get; set; }
}
static void Main(string[] args)
{
Dictionary<int, MyClass> dic =
new Dictionary<int, MyClass>();
//添加
dicAdd(1, new MyClass { Name = "张三", IsTrue = false });
dicAdd(2, new MyClass { Name = "张四", IsTrue = true });
dicAdd(3, new MyClass { Name = "张五", IsTrue = false });
dicAdd(4, new MyClass { Name = "张六", IsTrue = true });
dicAdd(5, new MyClass { Name = "张七", IsTrue = false });
int c1 = dicCount(e => eValueIsTrue == true);
ConsoleWriteLine(c1); //输出2
int c2 = dicCount(e => eValueIsTrue == false);
ConsoleWriteLine(c2); //输出3
// 或者
var qry1 = from x in dic
where xValueIsTrue == true
select x;
int c3 = qry1Count();
ConsoleWriteLine(c3); //输出2
var qry2 = from x in dic
where xValueIsTrue == false
select x;
int c4 = qry2Count(); //输出3
ConsoleWriteLine(c4);
}
}
}
取这串字符串中最大的数字？
string k = "abcdefghijklmnopsadjlvas094i029340$#%#&^%%$000888";var max =kAsQueryable()Where(o => o >= 48 && o <= 57)Max();
console？
int h=10;
for(int i=1;i<=h;i++)
{
ConsoleWriteLine(“”padleft(i,''));
｝
for(int i=h-1;i>0;i--)
{
ConsoleWriteLine(“”padleft(i,''));
}
storeDBAlbumsOrderByDescending(a => aOrderDetailsCount())Take(count)ToList();
数据上下文Albums数据表倒序排序(条件为按照各数据关联的OrderDetails数据表中数据的条数)拿记录(count条)立即执行转为list
使用join来连接
EnumerableJoin<TOuter, TInner, TKey, TResult> 方法 (IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, TInner, TResult>)
发送反馈
使用默认的相等比较器对键进行比较。
命名空间： SystemLinq
程序集： SystemCore（在 SystemCoredll 中）
语法
--------------------------------------------------------------------------------
VBC#C++F#JScript以带有颜色区分的格式查看复制到剪贴板打印<ExtensionAttribute> _
Public Shared Function Join(Of TOuter, TInner, TKey, TResult) ( _
outer As IEnumerable(Of TOuter), _
inner As IEnumerable(Of TInner), _
outerKeySelector As Func(Of TOuter, TKey), _
innerKeySelector As Func(Of TInner, TKey), _
resultSelector As Func(Of TOuter, TInner, TResult) _
) As IEnumerable(Of TResult)
<ExtensionAttribute> _
Public Shared Function Join(Of TOuter, TInner, TKey, TResult) ( _
outer As IEnumerable(Of TOuter), _
inner As IEnumerable(Of TInner), _
outerKeySelector As Func(Of TOuter, TKey), _
innerKeySelector As Func(Of TInner, TKey), _
resultSelector As Func(Of TOuter, TInner, TResult) _
) As IEnumerable(Of TResult)
public static IEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(
this IEnumerable<TOuter> outer,
IEnumerable<TInner> inner,
Func<TOuter, TKey> outerKeySelector,
Func<TInner, TKey> innerKeySelector,
Func<TOuter, TInner, TResult> resultSelector
)
public static IEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(
this IEnumerable<TOuter> outer,
IEnumerable<TInner> inner,
Func<TOuter, TKey> outerKeySelector,
Func<TInner, TKey> innerKeySelector,
Func<TOuter, TInner, TResult> resultSelector
)
[ExtensionAttribute]
public:
generic<typename TOuter, typename TInner, typename TKey, typename TResult>
static IEnumerable<TResult>^ Join(
IEnumerable<TOuter>^ outer,
IEnumerable<TInner>^ inner,
Func<TOuter, TKey>^ outerKeySelector,
Func<TInner, TKey>^ innerKeySelector,
Func<TOuter, TInner, TResult>^ resultSelector
)
[ExtensionAttribute]
public:
generic<typename TOuter, typename TInner, typename TKey, typename TResult>
static IEnumerable<TResult>^ Join(
IEnumerable<TOuter>^ outer,
IEnumerable<TInner>^ inner,
Func<TOuter, TKey>^ outerKeySelector,
Func<TInner, TKey>^ innerKeySelector,
Func<TOuter, TInner, TResult>^ resultSelector
)
static member Join :
outer:IEnumerable<'TOuter>
inner:IEnumerable<'TInner>
outerKeySelector:Func<'TOuter, 'TKey>
innerKeySelector:Func<'TInner, 'TKey>
resultSelector:Func<'TOuter, 'TInner, 'TResult> -> IEnumerable<'TResult>
static member Join :
outer:IEnumerable<'TOuter>
inner:IEnumerable<'TInner>
outerKeySelector:Func<'TOuter, 'TKey>
innerKeySelector:Func<'TInner, 'TKey>
resultSelector:Func<'TOuter, 'TInner, 'TResult> -> IEnumerable<'TResult>
类型参数
TOuter
第一个序列中的元素的类型。
TInner
第二个序列中的元素的类型。
TKey
键选择器函数返回的键的类型。
TResult
结果元素的类型。
参数
outer
类型： SystemCollectionsGenericIEnumerable <TOuter>
要联接的第一个序列。
inner
类型： SystemCollectionsGenericIEnumerable <TInner>
要与第一个序列联接的序列。
outerKeySelector
类型： SystemFunc <TOuter, TKey>
用于从第一个序列的每个元素提取联接键的函数。
innerKeySelector
类型： SystemFunc <TInner, TKey>
用于从第二个序列的每个元素提取联接键的函数。
resultSelector
类型： SystemFunc <TOuter, TInner, TResult>
用于从两个匹配元素创建结果元素的函数。
返回值
类型： SystemCollectionsGenericIEnumerable <TResult>
一个具有 TResult 类型元素的 IEnumerable<T>，这些元素是通过对两个序列执行内部联接得来的。
使用说明
在 Visual Basic 和 C# 中，可以在 IEnumerable<TOuter> 类型的任何对象上将此方法作为实例方法来调用。当使用实例方法语法调用此方法时，请省略第一个参数。有关更多信息，请参见 扩展方法 (Visual Basic)或 扩展方法（C# 编程指南）。
异常
--------------------------------------------------------------------------------
异常 条件
ArgumentNullException
outer 或 inner 或 outerKeySelector 或 innerKeySelector 或 resultSelector 为 null。
备注
--------------------------------------------------------------------------------
此方法通过使用延迟执行实现。
即时返回值为一个对象，该对象存储执行 *** 作所需的所有信息。
只有通过直接调用对象的 GetEnumerator 方法或使用 Visual C# 中的 foreach（或 Visual Basic 中的 For Each）来枚举该对象时，才执行此方法表示的查询。
使用默认的相等比较器 Default 对键进行哈希处理和比较。
联接是指基于某个公共键使两个信息源的元素相关联的 *** 作。
Join 在一个方法调用中产生两个信息源和使它们相匹配的密钥。
这与 SelectMany 的用法不同，后者需要一个以上的方法调用才可以执行相同的 *** 作。
Join 保留 outer 中的元素的顺序，并且对于这些元素中的每一个元素，保留 inner 中的匹配元素的顺序。
在查询表达式语法中， join (Visual C#) 或 Join (Visual Basic) 子句转换为 Join 的一个调用。
在关系数据库术语中， Join 方法实现内部同等联接。'
“内部”表示结果中仅包含在另一序列中具有匹配项的元素。
“同等联接”是在其中比较键是否相等的联接。
左外部联接 *** 作没有专用的标准查询运算符，但可以使用 GroupJoin 方法执行此 *** 作。
请参见 联接运算。
示例
--------------------------------------------------------------------------------
下面的代码示例演示如何使用 Join<TOuter, TInner, TKey, TResult>(IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, TInner, TResult>) 基于公共键对两个序列执行内部联接。
VBC#C++F#JScript以带有颜色区分的格式查看复制到剪贴板打印Structure Person
Public Name As String
End Structure
Structure Pet
Public Name As String
Public Owner As Person
End Structure
Sub JoinEx1()
Dim magnus As New Person With {Name = "Hedlund, Magnus"}
Dim terry As New Person With {Name = "Adams, Terry"}
Dim charlotte As New Person With {Name = "Weiss, Charlotte"}
Dim barley As New Pet With {Name = "Barley", Owner = terry}
Dim boots As New Pet With {Name = "Boots", Owner = terry}
Dim whiskers As New Pet With {Name = "Whiskers", Owner = charlotte}
Dim daisy As New Pet With {Name = "Daisy", Owner = magnus}
Dim people As New List(Of Person)(New Person() {magnus, terry, charlotte})
Dim pets As New List(Of Pet)(New Pet() {barley, boots, whiskers, daisy})
' Create a list of Person-Pet pairs, where each element is an
' anonymous type that contains a Pet's name and the name of the
' Person that owns the Pet
Dim query = _
peopleJoin(pets, _
Function(person) person, _
Function(pet) petOwner, _
Function(person, pet) _
New With {OwnerName = personName, Pet = petName})
Dim output As New SystemTextStringBuilder
For Each obj In query
outputAppendLine(objOwnerName & " - " & objPet)
Next
' Display the output
MsgBox(outputToString)
End Sub
' This code produces the following output:
'
' Hedlund, Magnus - Daisy
' Adams, Terry - Barley
' Adams, Terry - Boots
' Weiss, Charlotte - Whiskers
Structure Person
Public Name As String
End Structure
Structure Pet
Public Name As String
Public Owner As Person
End Structure
Sub JoinEx1()
Dim magnus As New Person With {Name = "Hedlund, Magnus"}
Dim terry As New Person With {Name = "Adams, Terry"}
Dim charlotte As New Person With {Name = "Weiss, Charlotte"}
Dim barley As New Pet With {Name = "Barley", Owner = terry}
Dim boots As New Pet With {Name = "Boots", Owner = terry}
Dim whiskers As New Pet With {Name = "Whiskers", Owner = charlotte}
Dim daisy As New Pet With {Name = "Daisy", Owner = magnus}
Dim people As New List(Of Person)(New Person() {magnus, terry, charlotte})
Dim pets As New List(Of Pet)(New Pet() {barley, boots, whiskers, daisy})
' Create a list of Person-Pet pairs, where each element is an
' anonymous type that contains a Pet's name and the name of the
' Person that owns the Pet
Dim query = _
peopleJoin(pets, _
Function(person) person, _
Function(pet) petOwner, _
Function(person, pet) _
New With {OwnerName = personName, Pet = petName})
Dim output As New SystemTextStringBuilder
For Each obj In query
outputAppendLine(objOwnerName & " - " & objPet)
Next
' Display the output
MsgBox(outputToString)
End Sub
' This code produces the following output:
'
' Hedlund, Magnus - Daisy
' Adams, Terry - Barley
' Adams, Terry - Boots
' Weiss, Charlotte - Whiskers
帅哥的意思是想从数据库中选取一字段，然后单击button后就将选出的数据填充到listbox控件里头是不？
如果是的话我建议公共方法那里返回dataset，然后用for循环添加到listbox里头，举个例子吧：
公共方法这样写：
public DataSet sql_dataset(string str_command,string str_tablename)//返回数据集对象，参数为查询语句和表名
{
myconnectionOpen();DataSet myset = new DataSet();
myadapter = new SqlDataAdapter(str_command, myconnection);
mysetClear();
mysetReset();
myadapterFill(myset, str_tablename);
myconnectionClose();
return myset；
}
然后button的事件处理方法里头可以这样调用：
private void button1_Click(object sender, EventArgs e)
{
string str_select = "select from Message_list";
DataSet myset=new DataSet();//声明一个新的数据集接收返回的数据集
myset = cdsql_dataset(str_select, "Message_list");
int i = mysetTables[0]RowsCount;//记录总行数
ListBox1Itemsclear()；//清空以前选项
for (int i2 = 0; i2 < i; i2++)
{
thisListBox1ItemsAdd(mysetTables[0]Rows[i2][0]ToString());
}
}
using System;
using SystemCollectionsGeneric;
using SystemLinq;
using SystemText;
using MicrosoftOfficeInteropExcel;
using SystemData;
namespace ExcelTest
{
public class ExcelUtil
{
SystemDataDataTable table11 = new SystemDataDataTable();
public void ExportToExcel(SystemDataDataTable table, string saveFileName)
{
bool fileSaved = false;
//ExcelApp xlApp = new ExcelApp();
Application xlApp = new Application();
if (xlApp == null)
{
return;
}
Workbooks workbooks = xlAppWorkbooks;
Workbook workbook = workbooksAdd(XlWBATemplatexlWBATWorksheet);
Worksheet worksheet = (Worksheet)workbookWorksheets[1];//取得sheet1
long rows = tableRowsCount;
/下边注释的两行代码当数据行数超过行时，出现异常：异常来自HRESULT:0x800A03EC。因为：Excel 2003每个sheet只支持最大行数据
//Range fchR = worksheetget_Range(worksheetCells[1, 1], worksheetCells[tableRowsCount+2, gridviewColumnsViewVisibleColumnsCount+1]);
//fchRValue2 = datas;/
if (rows > 65535)
{
long pageRows = 60000;//定义每页显示的行数,行数必须小于
int scount = (int)(rows / pageRows);
if (scount pageRows < tableRowsCount)//当总行数不被pageRows整除时，经过四舍五入可能页数不准
{
scount = scount + 1;
}
for (int sc = 1; sc <= scount; sc++)
{
if (sc > 1)
{
object missing = SystemReflectionMissingValue;
worksheet = (MicrosoftOfficeInteropExcelWorksheet)workbookWorksheetsAdd(
missing, missing, missing, missing);//添加一个sheet
}
else
{
worksheet = (Worksheet)workbookWorksheets[sc];//取得sheet1
}
string[,] datas = new string[pageRows + 1, tableColumnsCount+ 1];
for (int i = 0; i < tableColumnsCount; i++) //写入字段
{
datas[0, i] = tableColumns[i]Caption;
}
Range range = worksheetget_Range(worksheetCells[1, 1], worksheetCells[1, tableColumnsCount]);
rangeInteriorColorIndex = 15;//15代表灰色
rangeFontBold = true;
rangeFontSize = 9;
int init = intParse(((sc - 1) pageRows)ToString());
int r = 0;
int index = 0;
int result;
if (pageRows sc >= tableRowsCount)
{
result = tableRowsCount;
}
else
{
result = intParse((pageRows sc)ToString());
}
for (r = init; r < result; r++)
{
index = index + 1;
for (int i = 0; i < tableColumnsCount; i++)
{
if (tableColumns[i]DataType == typeof(string) || tableColumns[i]DataType == typeof(Decimal) || tableColumns[i]DataType == typeof(DateTime))
{
object obj = tableRows[r][tableColumns[i]ColumnName];
datas[index, i] = obj == null "" : "'" + objToString()Trim();//在objToString()前加单引号是为了防止自动转化格式
}
}
}
Range fchR = worksheetget_Range(worksheetCells[1, 1], worksheetCells[index + 2, tableColumnsCount + 1]);
fchRValue2 = datas;
worksheetColumnsEntireColumnAutoFit();//列宽自适应。
range = worksheetget_Range(worksheetCells[1, 1], worksheetCells[index + 1, tableColumnsCount]);
//15代表灰色
rangeFontSize = 9;
rangeRowHeight = 1425;
rangeBordersLineStyle = 1;
rangeHorizontalAlignment = 1;
}
}
else
{
string[,] datas = new string[tableRowsCount + 2, tableColumnsCount + 1];
for (int i = 0; i < tableColumnsCount; i++) //写入字段
{
datas[0, i] = tableColumns[i]Caption;
}
Range range = worksheetget_Range(worksheetCells[1, 1], worksheetCells[1, tableColumnsCount]);
rangeInteriorColorIndex = 15;//15代表灰色
rangeFontBold = true;
rangeFontSize = 9;
int r = 0;
for (r = 0; r < tableRowsCount; r++)
{
for (int i = 0; i < tableColumnsCount; i++)
{
if (tableColumns[i]DataType == typeof(string) || tableColumns[i]DataType == typeof(Decimal) || tableColumns[i]DataType == typeof(DateTime))
{
object obj = tableRows[r][tableColumns[i]ColumnName];
datas[r + 1, i] = obj == null "" : "'" + objToString()Trim();//在objToString()前加单引号是为了防止自动转化格式
}
}
//SystemWindowsFormsApplicationDoEvents();
}
Range fchR = worksheetget_Range(worksheetCells[1, 1], worksheetCells[tableRowsCount + 2, tableColumnsCount + 1]);
fchRValue2 = datas;
worksheetColumnsEntireColumnAutoFit();//列宽自适应。
range = worksheetget_Range(worksheetCells[1, 1], worksheetCells[tableRowsCount + 1, tableColumnsCount]);
//15代表灰色
rangeFontSize = 9;
rangeRowHeight = 1425;
rangeBordersLineStyle = 1;
rangeHorizontalAlignment = 1;
}
if (saveFileName != "")
{
try
{
workbookSaved = true;
workbookSaveCopyAs(saveFileName);
fileSaved = true;
}
catch (Exception ex)
{
fileSaved = false;
}
}
else
{
fileSaved = false;
}
xlAppQuit();
GCCollect();//强行销毁
}
}
}
以上就是关于在 c# 或 vb.net 如何使用 LINQ 统计 Dictionary 中符合条件的对象数量全部的内容，包括:在 c# 或 vb.net 如何使用 LINQ 统计 Dictionary 中符合条件的对象数量、C# LINQ提取数字值最大的数字字符串、C#实验，输出菱形，用循环语句写，跪求代码等相关内容解答，如果想了解更多相关内容，可以关注我们，你们的支持是我们更新的动力！
欢迎分享，转载请注明来源：内存溢出
微信扫一扫
支付宝扫一扫
评论列表（0条）