Error while populating datagrid using ASync Call

Question

Hi All I am using Async call to populate datagrid by following code. This code I have written in a class which inherit in other class. This class has a virtual method which is overridden in derived class. Problem I am facing is datagrid is populated and displayed sometimes and not every time I load the page. I already checked the rowcount in table that I am assigning to grid. I am getting the proper row count. I have declaired a delegate and using BegingInvoke and EndEnvoke method for it. FYI flgrd is an object of delegate. private void CallAsyncMethod() { flgrd = new FillGrid (processData); flgrd.BeginInvoke( new AsyncCallback ( this .callAsyncResultMethod) flgrd); } private void callAsyncResultMethod( IAsyncResult ar) { flgrd = (( FillGrid )(ar.AsyncState)); flgrd.EndInvoke(ar); } public virtual void GetData() { // User will write code in derived class to populate datagrid. } private void processData() { this .GetData(); }

Ashish · Answer

Hi Thanks for u r rlp Actually my req'nt is bit different let me explain u... I am creating a class which willl have a virtual getdata() method that can be overridden in derived class. In base class I am creating a delegate for and using Begin and EndEnvoke method for Async call to DB. here's my sample class: public class Class1 : System.Web.UI.WebControls.WebParts. WebPart { private delegate void FillGrid (); private FillGrid flgrd = null ; protected override void OnLoad( EventArgs e) { base .OnLoad(e); CallAsyncMethod(); } private void CallAsyncMethod() { flgrd = new FillGrid (processData); flgrd.BeginInvoke( new AsyncCallback ( this .callAsyncResultMethod) flgrd); } private void callAsyncResultMethod( IAsyncResult ar) { flgrd = (( FillGrid )(ar.AsyncState)); flgrd.EndInvoke(ar); } protected virtual void GetData() { } private void processData() { this .GetData(); } } this is used to populate grid on web part above one is my template which I will inherit in my other class and override the getdata() method. Prob: Grid is not getting displayed every time I load the page. pls help me. Thanks in advance....

Matthew Cochran · Answer

I didn't quite understand your architecture. Your async method should be the one retrieving data (which would be the long-running process). Try something like this: public partial class Form1 : Form { public Form1() { InitializeComponent(); button1.Click += (snd arg) => CallAsyncMethod(); // wiring up the event } public delegate IEnumerable String > GetData (); public delegate void ProcessResult ( IAsyncResult result); private void CallAsyncMethod() { GetData getter = LongRunningDataFetcher; getter.BeginInvoke(callAsyncResultMethod getter); } private void callAsyncResultMethod( IAsyncResult ar) { // make sure this is running on the main // form's thread if ( this .InvokeRequired) { this .Invoke( new ProcessResult (callAsyncResultMethod) ar); return ; // don't execute on this thread } GetData getter = ar.AsyncState as GetData ; // test getter for null IEnumerable String > source = getter.EndInvoke(ar); // test souce for null dataGridView1.DataSource = source; } private IEnumerable String > LongRunningDataFetcher() { // this would be the long-running process method... // you can make this virtual and delete the implementation // here in order to make a sub-class implement it. return new String []{ one  two  three }; } }