JsonDataSource.FillAsync(IEnumerable<IParameter>, CancellationToken) Method
Populates the JsonDataSource in an asynchronous manner, uses the sourceParameters parameter to pass external parameters to the data source and the cancellationToken parameter to send the cancellation signal.
Namespace: DevExpress.DataAccess.Json
Assembly: DevExpress.DataAccess.v20.2.dll
NuGet Packages: DevExpress.DataAccess, DevExpress.WindowsDesktop.DataAccess
Declaration
public Task FillAsync(
IEnumerable<IParameter> sourceParameters,
CancellationToken cancellationToken
)Parameters
| Name | Type | Description |
|---|---|---|
| sourceParameters | IEnumerable<IParameter> | External parameters passed to the data source. |
| cancellationToken | CancellationToken | A cancellation token that the task observes. |
Returns
| Type | Description |
|---|---|
| Task | A task that populates the data source. |
Remarks
Use this method to populate a JSON data source in an individual task asynchronously. Unlike the Fill() method call, FillAsync does not lock other actions performed concurrently. For instance, the user interface remains operational while the data source is populated.
Call the FillAsync method with the await operator.
The sourceParameters parameter passes a collection of external parameters to the data source. For instance, you can pass report parameters from a reporting application and use report parameter values to specify the JsonDataSource‘s PathParameters, QueryParameters, or HeaderParameters.
The cancellationToken parameter provides a way to send the cancellation signal to the task. The task monitors the token and stops when it receives the signal. Create a CancellationTokenSource class instance and pass its Token property to the FillAsync method call. Call the CancellationTokenSource.Cancel method to stop the task.
Handle the FillError event, or catch the JsonDataSourceException exception, to process the case when the FillAsync method failed to populate the data source.
Example
The code sample below is a reporting application that uses JsonDataSource to provide data to a report. The data source is populated with data in an asynchronous manner. The FileNameParameter report parameter is passed to the data source to specify the endpoint file name. A CancellationTokenSource class instance is used to allow users to interrupt the data source fill process if it takes too long.
using System.Threading;
using System.Threading.Tasks;
using DevExpress.DataAccess;
using DevExpress.DataAccess.Json;
// ...
// Use the cancellationTokenSource to allow users to stop filling the data source.
CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
// ...
// The cancelButton_Click event handler uses cancellationTokenSource to stop filling the data source.
private void cancelButton_Click(object sender, EventArgs e) {
cancellationTokenSource.Cancel();
}
// ...
XtraReport report = new XtraReport();
report.Parameters.Add(new Parameter() {
Name = "FileNameParameter",
Type = typeof(string),
Value = "customers.json"
});
// Create a new JSON source.
var jsonSource = new UriJsonSource() {
Uri = new Uri(@"https://raw.githubusercontent.com/DevExpress-Examples/DataSources/master/JSON/")
};
jsonSource.PathParameters.Add(
// The "FileName" path parameter uses the external "FileNameParameter" parameter value.
new PathParameter("FileName", typeof(Expression), new Expression("?FileNameParameter"))
);
// Assign the JSON source to the data source.
var datasource = new JsonDataSource() {
JsonSource = jsonSource
};
await datasource.FillAsync(report.Parameters, cancellationTokenSource.Token);