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Creating object references
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À
09/07/2002 12:07:45
Jerry Tovar
Dana Corporation Dana It
Maumee, Ohio, États-Unis
Information générale
Forum:
ASP.NET
Catégorie:
Autre
Divers
Thread ID:
00676644
Message ID:
00676712
Vues:
22
What exactly are you trying to display? prop_myAccessConn is an object so you have to select what property you want to display.

e.g. Console.WriteLine(oclass1.prop_myAccessConn.Name);
Console.WriteLine(oclass1.prop_myAccessConn.ToString());

>Thanks, that worked.
>
>But now how do I access the prop_myAccessConn, prop_myAccessCommand and prop_myDataAdapter fields? They display as blank in class2 when I do this in class2:
>Console.WriteLine(oclass1.prop_myAccessConn);
>
>Thanks,
>
>Jerryt
>
>
>
>>You defined the DataSet variable but haven't initilized it. Do the following in Class1.
>>
>>public DataSet prop_myDataSet = new DataSet();
>>
>>
>>>Using C#.
>>>
>>>I am trying to create 2 classes. In class1, I am trying to define my OleDb connection vars/fields.
>>>
>>>In class2, I am trying to use these fields from class1 to query the datasource. However, when I run the project, I get the following error: "Object reference not set to an instance of an object"
>>>
>>>Here is what my C# code looks like: (Pseudo Code)
>>>
>>>///////////////////////////////////////////////////////////
>>>public class class1
>>>///////////////////////////////////////////////////////////
>>>//Fields:
>>> public string prop_strAccessConn;
>>> public string prop_strAccessSelect;
>>> public DataSet prop_myDataSet;
>>> public string prop_ctable;
>>> public string prop_myAccessConn;
>>> public string prop_myAccessCommand;
>>> public string prop_myDataAdapter;
>>>public class1() //Default constructor:
>>> prop_strAccessConn =
>>> "Provider=VFPOLEDB.1;Data Source=C:\\APPS\\MYDBC.DBC"
>>> prop_strAccessSelect = "SELECT * FROM mytable";
>>>
>>> OleDbConnection prop_myAccessConn = new OleDbConnection
>>> (prop_strAccessConn);
>>> OleDbCommand prop_myAccessCommand = new OleDbCommand
>>> (prop_strAccessSelect,prop_myAccessConn);
>>> OleDbDataAdapter prop_myDataAdapter = new OleDbDataAdapter
>>> (prop_myAccessCommand);
>>>
>>>public static void Main ()
>>>
>>>///Call class2 for processing.
>>>class2.processit();
>>>
>>>
>>>///////////////////////////////////////////////////////////
>>>public class class2
>>>///////////////////////////////////////////////////////////
>>>public static void processit ()
>>>
>>>Console.WriteLine("Write output to the console.");
>>>class1 oclass1 = new class1(); //Create object reference.
>>>oclass1.prop_myDataSet.Tables.Add("mytable"); //I get error here.
>>>
>>>
>>>I can't get the above example to work. However the following example does work but I would like to separate and make the OleDb vars accessible to other classes without redefining the vars.
>>>
>>>///Working example. Pseudo code.
>>>//////////////////////////////
>>>public class class1
>>>//////////////////////////////
>>>public static void Main ()
>>>string strAccessConn = "Provider=VFPOLEDB.1;Data Source=C:\\APPS\\CTRAK6\\CTTRAK.DBC"
>>>
>>>string strAccessSelect = "SELECT * FROM mytable";
>>>
>>>// Create the dataset and add the ctghead table to it:
>>>DataSet myDataSet = new DataSet();
>>>myDataSet.Tables.Add("mytable");
>>>
>>>// Create Access objects:
>>>OleDbConnection myAccessConn = new OleDbConnection(strAccessConn);
>>>OleDbCommand myAccessCommand = new OleDbCommand(strAccessSelect,myAccessConn);
>>>OleDbDataAdapter myDataAdapter = new OleDbDataAdapter(myAccessCommand);
>>>
>>>myAccessConn.Open();
>>>
>>>etc... everything works!
>>>
>>>
>>>What am I doing wrong with regards to defining OleDb information in class1 and accessing those objects in another class to query a datasource?
>>>
>>>Thanks,
>>>
>>>Jerryt
- Jayesh
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