参考或了解如何将其设置为对象 [英] Ref or out how to set it as object

问题描述

我有一个方法Thad将数据填充到网格并通过ref数据适配器对象返回，以便能够在行更新后更新网格中的数据...

和i疯狂的传递OLEDB或SQLDB数据适配器的方法变量

但是当我使用ref或Out to Data Adapter错误时出现



我尝试过：



这个代码来自方法

枚举ConnectionType 
 {
 SQL，
 OLEDB 
} 
 

 public void Grid（ConnectionType ADOType，GridControl obj，object cn，DataSet DS，ref object DA，ref DataTable DT，String DataTableName，string sqlString，params object [] Parameter）
 {
 
 if（ADOType == ConnectionType.OLEDB）
 {
 DataManagerOLEDB DM_ = new DataManagerOLEDB（）; 
 OleDbDataAdapter da =（OleDbDataAdapter）DA; 
 DM_.SelectFromTable（（OleDbConnection）cn，sqlString，DS，out da，
 DataTableName，Parameter）; 
} 
 else 
 {
 DataManagerSQL DM_ = new DataManagerSQL（）; 
 SqlDataAdapter da =（SqlDataAdapter）DA; 
 
 DM_.SelectFromTable（（SqlConnection）cn，sqlString，DS，out da，
 DataTableName，Parameter）; 
} 
 
 DT = DS.Tables [DataTableName]; 
 obj.DataSource = DT; 

当像这样的通行方法时

< pre> SurveyVar.fillDxControl.Grid（ConnectionType.OLEDB，grdSurvey，SurveyVar.cnSurvey，SurveyVar.DataSetSurvey，ref SurveyVar.DataAdapterSurvey，ref datSurvey，T002，sqlString，vParameters） ; 

数据适配器变量出现错误为

严重性代码描述项目文件行抑制状态
错误CS1503参数5：无法从'ref System.Data.OleDb.OleDbDataAdapter'转换为'ref object'调查F：\ BannaSQLSource \_New Application \ Source Code \SurveyApplication \ Application Caption \forms\frmSurvey.cs 125 Active 

解决方案

让我们稍微简化一下：

< pre lang =c＃> private void MyMethod（ ref object o）
{
}
private void MyButton_Click（ object sender，EventArgs ew）
{
OleDbDataAdapter da = < span class =code-keyword> new OleDbDataAdapter（）;
MyMethod（ ref da）;
...

为什么会收到错误消息：

无法从'ref System.Data.OleDb.OleDbDataAdapter转换'to'ref object'

想一想：o是对象的引用，所以你可以非常合理地在方法中放入任何类型的值：

< pre lang =c＃> private void MyMethod（ ref object o）
{
o = 你好;
}

如果系统允许你这样做，会有什么影响？



不愉快，就是这样。因为 o 是 ref ，所以对它的任何更改都会反映在调用方法参数变量中 - =在这种情况下， da 设置为字符串。因此，当控件返回到按钮单击事件并且代码尝试使用DataAdapter中的数据时，它会找到一个字符串，一切都开始失败。



As结果，你不能转换ref参数 - 类型必须完全匹配。

如果你需要将不同的对象类型作为ref参数传递，那么请考虑使用泛型。

I have a Method Thad Fill Data to Grid and return by ref data adapter object to able me to update data in grid after row update ...
and i Mad a Method to Pass OLEDB or SQLDB data adapter Variable
but when I use a ref or Out to Data Adapter error appear

What I have tried:

this a code from Method

enum ConnectionType
  {
      SQL,
      OLEDB
  }

public void Grid(ConnectionType ADOType, GridControl obj, object cn, DataSet DS, ref object DA, ref DataTable DT, String DataTableName, string sqlString, params object[] Parameter) 
        {

            if (ADOType == ConnectionType.OLEDB)
            {
                DataManagerOLEDB DM_ = new DataManagerOLEDB();
                OleDbDataAdapter da =  (OleDbDataAdapter)DA; 
                DM_.SelectFromTable((OleDbConnection)cn, sqlString, DS, out da, 
                DataTableName, Parameter);
            }
            else
            {
                DataManagerSQL DM_ = new DataManagerSQL();
                SqlDataAdapter da = (SqlDataAdapter)DA;

                DM_.SelectFromTable((SqlConnection)cn, sqlString, DS, out da, 
                DataTableName, Parameter);
            }
            
            DT = DS.Tables[DataTableName];
            obj.DataSource = DT;

when Pass Method like This

<pre>SurveyVar.fillDxControl.Grid(ConnectionType.OLEDB, grdSurvey, SurveyVar.cnSurvey, SurveyVar.DataSetSurvey, ref SurveyVar.DataAdapterSurvey,  ref datSurvey, "T002", sqlString, vParameters);               

Error appear on data adapter variable as "

Severity	Code	Description	Project	File	Line	Suppression State
Error	CS1503	Argument 5: cannot convert from 'ref System.Data.OleDb.OleDbDataAdapter' to 'ref object'	Survey	F:\BannaSQLSource\_New Application\Source Code\SurveyApplication\Application Caption\forms\frmSurvey.cs	125	Active

解决方案

Let's simplify this a little:

private void MyMethod(ref object o)
    {
    }
private void MyButton_Click(object sender, EventArgs ew)
    {
    OleDbDataAdapter da = new OleDbDataAdapter();
    MyMethod(ref da);
...

Why do you get an error saying:

cannot convert from 'ref System.Data.OleDb.OleDbDataAdapter' to 'ref object'

Think about it: o is a reference to an object, so you can very legitimately put any type of value into it inside the method:

private void MyMethod(ref object o)
    {
    o = "hello";
    }

If the system allowed you to do that, what effect would it have?

Unpleasant, that's what. Because o is a ref, any changes to it are reflected in the calling method parameters variables -= in this case, da gets set to a string. So when control goes back to the button click event and the code tries to use the data in the DataAdapter, it finds a string and everything starts to fall over.

As a result, you can't cast a ref parameter - the type must match exactly.
If you need to pass different object types as ref parameters, then consider using generics instead.

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