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I have a C++ dll that opens an image file using GDI+ and gets a thumbnail of the opened image using GetThumbnailImage. I would like the C++ DLL to be able to return a pointer to the Image and then have a custom C# control of mine display it. Does anyone know how I can share this image information between the two languages? (I know I can use C#'s GDI image functions to create the thumbnail also, but the C++ version is much faster).
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You could have the C++ dll return the handle to the image using the GDI+ Bitmap.GetHBitmap(). Your C# control could then get an IntPtr containing the handle to the bitmap and use Image.FromHBitmap() to get the image object back.
Human beings were not meant to sit in little cubicles staring at computer screens all day, filling out useless forms and listening to eight different bosses drone on about about mission statements. -- Peter Gibbons
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Hi
I have three Combo boxes .When the value in first combobox is selected second combo is populated and with the second value the third is pupulated.
i am using event selectedIndexChnged with each combo.
On form Load i am populating the First combo with setting its datasource property. when i set the text feild and value feild the selected index is called where i have code to populate second combobox. but the prolem is i need the selected value but that si not set proprely while the form loads and it gives error. any way to do that.
Thanks
monica
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Gosh, this has been asked a lot lately. If you set the datasource in the first combo all the time, it will reset the selected index. Set it in a if (!IsPostback) block, so that it only gets set the first time through.
Christian Graus - Microsoft MVP - C++
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can u pls elaborate a bit more.
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well, the page class has a property, IsPostback. That tells your page if you're viewing for the first time, or not. If you don't use this, and you set the datasource every time you load the page, including postback, you will lose your selected index, because it will revert to the first item of the data source you've just set. SO, when you set the data source and databind, you should first check if the page is being loaded for the first time. IF not, your ViewSate contains the contents of the control, as well as the selected Index, and you don't want to replace that.
if (!IsPostBack)
{
combo1.DataSource = GetDataSource();
combo1.DataBind();
}
Christian Graus - Microsoft MVP - C++
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i Think i was unable to explain my problem I am making a windows application. i am not changing the datasource of my first combo after the form is loaded. My problem taht first time when i set the datasource property of my first combo then it calls its SelectedIndexChanged where i am having code to populate the second combo by querying for selectedvalueof first combo. and similary for third one.
is any simpler solution which works is there
Thanks
Monica
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monica2k wrote:
I am making a windows application
Oh, OK. 
So you're saying that the selected index does not exist when you get a selected index changed event ? Or what ? I think you need to post some code.
Christian Graus - Microsoft MVP - C++
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This Is my Main Combo Code
To populate
public static void PopulateMainCombo( ComboBox Combo, string ConnectionString, string TableName, string TextField, string ValueField, string DefaultValue )
{ Combo.DataSource = null;
string Query="select * from " + TableName;
Query = Query + " order by " + TextField;
Combo.DataSource=DataManager.ConnectingForCombo(ConnectionString,Query,TableName);
Combo.DisplayMember = TextField;
Combo.ValueMember = ValueField;
}
private void cmbMainDiagnosis_SelectedIndexChanged(object sender, System.EventArgs e)
{
bool blnVisible;
blnSubDiagnosis=false;
int intSelectedValue;
intSelectedValue=(int) this.cmbMainDiagnosis.SelectedValue;
cmbSubDiagnosis.Visible=false;
cmbSubSubDiagnosis.Visible=false;
blnVisible=Diagnosis.SetDiagnosisCombos(intSelectedValue,this.cmbSubDiagnosis,"tblsubdiagnosis_mas","strSubDiagnosisDesc","intMainDiagnosisCode","0");
blnSubDiagnosis=blnVisible;
if (blnVisible==true)
{
cmbSubDiagnosis.Visible=true;
}
else
cmbSubDiagnosis.Visible=false;
}
/////////////////////////////////////////////////////////////////////////////
and this is my Second Combo that is cmbsubDiagnosis on change of which my third combo that is cmbSubSubDiagnisis is to be populated.
////////////////////////////////////////////////////////////////////////////
private void cmbSubDiagnosis_SelectedIndexChanged(object sender, System.EventArgs e)
{
if (blnSubDiagnosis==true)
{
bool blnVisible;
int intSelectedValue;
intSelectedValue=(int)this.cmbSubDiagnosis.SelectedValue;
cmbSubSubDiagnosis.Visible=false;
blnVisible=Diagnosis.SetDiagnosisCombos(intSelectedValue,this.cmbSubSubDiagnosis,"tblsubsubdiagnosis_mas","strSubsubDiagnosisDesc","intSubDiagnosisCode","0");
if (blnVisible==true)
{
cmbSubSubDiagnosis.Visible=true;
}
else
cmbSubSubDiagnosis.Visible=false;
}
}
///////////////////////////////////////////////////////////////////////////
and this is the function i use to puplate 2nd and 3 rd combo
///////////////////////////////////////////////////////////////////////////
public static bool SetDiagnosisCombos(int paramDiagnosisCode,ComboBox Combo,string TableName, string TextField, string ValueField, string DefaultValue )
{
String ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["DSN"];
Combo.DataSource = null;
String query = "select * from "+ TableName +" where "+ ValueField + " = " + paramDiagnosisCode;
DataTable Dt = DataManager.ExecuteQuery(ConnectionString, query, TableName );
if (Dt.Rows.Count!=0)
{
Combo.DataSource=Dt;
Combo.DisplayMember = TextField;
Combo.ValueMember = ValueField;
Combo.SelectedIndex = -1;
return true;
}
else
return false;
}
pls i am struggling since morning. Help me out pls. the problem comes at the bold points an exception is thrown which says additional information required
Monica
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And what goes wrong ?
=(int)this.cmbSubDiagnosis.SelectedValue;
Is it possible that selectedValue is a string and you need Convert.ToInt16 instead of the cast ?
Christian Graus - Microsoft MVP - C++
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yes exactly the problem comes here.
what to do next
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1. Change (int) to Convert.ToInt32( (like I said )
2. Step through the debugger in future to see what's going on when you've got a line that blows up
3. Next time you ask a question, if you know where the code blows up, then give us the code, and either way, tell us what the error is you're getting.
Christian Graus - Microsoft MVP - C++
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Its Still giving error at the same point and the error is
An unhandled exception of type 'System.InvalidCastException' occurred in mscorlib.dll
Additional information: Specified cast is not valid.
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Step 2 - use the debugger to find why the Value can't cast to a number.
Christian Graus - Microsoft MVP - C++
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when i used the debugger it shows that the selectedvalue has
"System.Data.DataRowView" value that is why its not converting it but what is the solution to it.
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OK, so that's what you need to cast it to, and then get the value out of it.
Christian Graus - Microsoft MVP - C++
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Casting to Int32 is also not working . It is giving same error
Is there any other way to achive my aim.Now where should i look. I am doing nothing different. Is there any other way to fill the combo with the rows from table with their code as value member.
or is there any otehr event which i can use.
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Instead of casting to Int32 you have to first cast to System.Data.DataRowView. If you have this you can use its indexer to access the element you need. After that cast this element to Int32 and you are done.
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how to do that can u pls explain i am new to C#
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are you getting this problem only when the form is loading??
Afzal Hassen
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As Im really in a hurry here just a small snippet:
DataRovwView drv = (DataRowView)this.cmbSubDiagnosis.SelectedValue;
int myIntValue = (int)drv[IndexOrNameOfTheColumnYouWishToAccess];
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Your core problem is that you're shoving a datarowview into the value, the problem really is when you set the data source. You need to tell the combo which property to use to set the value for each row. The problem has nothing to do with the event. You have a datarowview in the value, you cannot magically turn it into an int, you need to either get it out as a datarowview ( which is what it is ) and then work out where your number is or, preferably, you need to fix the code that sets the datasource, so that it does in fact contain an int as you were hoping.
In general, these 'please help me, something blows up' posts are useless, look how long it took us to get to the heart of the problem. You should learn to use your debugger. You'll get your answer a lot quicker if you post something like 'this line throws an invalid cast exception and the value in the row that I'm trying to cast is a datarowview.' A few seconds in the debugger will tell you that, and as you learn C#, that's the path you'd follow to fix the problem, by first knowing what it is.
Christian Graus - Microsoft MVP - C++
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Thanks
i will try to follow ur instructions .
monica
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I know you take a performance hit if you make your methods virtual, but do you take a similar hit when you use abstract methods
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Abstract methods are also virtual, it's just that they don't have any implementation in the base class. If you look into the generated IL, you'll see that they are declared virtual (plus abstract) and that method calls are translated to callvirt, which is IL speak for calling a virtual method.
Regards
Senthil
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