System.ArgumentNullException: Value cannot be null. This object carries information about the requested data items. The OnRead event handler receives an argument, which inherits from ReadEventArgs. The Telerik TreeList for Blazor is a powerful component, which allows you . However, its not clear to me whether that would provide a better user experience: The user might find that having the data change as they page back is more disconcerting than helpful (especially if data has been added or deleted at the data source because that would cause the data to shift from one page to another in the grid). But even ignoring the updates, youve now got the opportunity to provide your user with a faster grid and better UX than if you fetched all your data up front. When the grid thinks its displayed all of the available items, it automatically disables its page-forward buttons. Most examples do not use OnRead to load data, instead using OnInitializedAsync (). In fact, theres a lot to be said for knowing, in advance, the number of items available from the data source. Group the grid by the Team and/or Vacation columns to see the effect. For example, it is possible to use custom sorting and filtering algorithms, if the built-in ones do not fit a given scenario. 0:25 Overview 1:25 TelerikRootComponent 2:02 Adding the TelerikGrid 2:32 DataSource 2:40 Grid Columns 4:00 Enabling Sorting, Filtering, Paging Links: - Give the Blazor Grid . This article presents the OnRead event and describes how to use it to data bind Telerik Blazor components. Regards, Download free 30-day trial. How to refresh the component data when using, Search by multiple data fields in ComboBox and DropDownList. //MyData = new ObservableCollection(); //OK! Progress collects the Personal Information set out in our Privacy Policy and Privacy Policy for California Residents and uses it for the purposes stated in that policy. This Blazor Grid - Persist State demo is part of a unique collection of hundreds of Blazor demos, with which you can see all Telerik Blazor components and their features in action. And faster is always better. Data operations are intentionally slowed down for the purpose of the demo. They are grouped logically. In this mode, the Grid behaves as usual when there is no grouping, and you can use this together with Virtual Scrolling for the rows. When reducing the impact on the clients memory is critical you can achieve all these goals using the Telerik UI for Blazor DataGrid's OnRead method. The ComboBox handler receives ComboBoxReadEventArgs, and so on. OnRead also offloads data operations outside the component, for example on the remote server. Progress, Telerik, and certain product names used herein are trademarks or registered trademarks of Progress Software Corporation and/or one of its subsidiaries or affiliates in the U.S. and/or other countries. However, by leveraging the DataGrid's OnRead event, you can retrieve data on an "as you need it" basis, fetching objects only as the user pages forward through the grid. By default, the Grid will receive the entire collection of data, and it will perform the necessary operations (like paging, sorting, filtering) internally. If the Grid starts with grouping set, it will make one request for the list of all groups, and will keep them in memory for paging. "Out of the box," the DataGrid doesn't support other data sources. Im going to assume, because Im trying to speed up my initial display time, that I dont want to make an extra call to determine the total number of items. Once grouping is applied (either manually by the user, or through the Grid state), the groups will now show up collapsed by default. Telerik and Kendo UI are part of Progress product portfolio. The method is part of the Telerik DataSource Extensions. Founded in 1976 to provide independent brokerages with a powerful marketing and referral program for luxury listings, the Sotheby's International Realty network was designed to connect the finest independent real estate companies to the most prestigious clientele in the world. If you decide that you want to be removed from our mailing lists at any time, you can change your contact preferences by clicking here. Large amounts of data require loading in chunks and on demand. Finally, I need to keep track of when Ive pulled all the data from the data source so I also set up a Boolean field called EOF. Telerik UI for Blazor Data Grid Watch on Data Binding The are two main ways to provide data to the Grid - via the Data parameter and via the OnRead event. That makes my TelerikGrid declaration look like this: In my code, those required fields look like this: I also need three other fields. Subscribe to the OnRead event. Virtual Classroom, the free self-paced technical training that gets you up to speed with Telerik and Kendo UI products quickly just got a fresh new look + new and improved content including a brand new Blazor course! This can improve WebAssembly application performance. There is also a runnable code example. I agree to receive email communications from Progress Software or its Partners, containing information about Progress Softwares products. The total number of items in the datasource. Add Product. It shows how to edit data, and save or revert changes in bulk. We have data coming from an API endpoint that handles paging, filtering, and sorting, so we are using manual data source operations through OnRead. All Rights Reserved. In case your data set is large you can take advantage of the OnRead event exposed by the Grid. Bus operators. When an observable collection is .Clear()-ed, the grid monitors that and updates its data. See Trademarks for appropriate markings. Progress is the leading provider of application development and digital experience technologies. ToDataSourceResult returns a DataSourceResult object. Since group headers and footers are treated like rows in the grid, the group headers may remain on a previous page from the data when you page the grid. It is possible to use DataSourceRequest, ToDataSourceResult and ToDataSourceResultAsync in scenarios, which are not related to a specific Telerik component. The following Blazor components expose an OnRead event. Now that you have bound the OnRead event, it will fire. Here are just a few examples, but there are many more possible scenarios: OnRead enables data binding to OData services. It will force the component to fire OnRead and receive new data. Use TValue with the AutoComplete, ComboBox, DropDownList, and MultiSelect.) All Rights Reserved. All Rights Reserved. While grouping is active, paging and virtual scrolling operations do not trigger OnRead, because the Grid already has all the group headers and all the items from the currently expanded groups. Regards, Changing OnRead to async makes no difference. One of the ways to filter the Telerik UI for Blazor Grid is by using the built-in Toolbar SearchBox. Change something in the grid ( edit an item, sort, filter, and so on) to see the built-in loading animation. Now that you have bound the OnRead event, it will fire. Without that collection, Id have to main the totalCount field myself as the maximum number of items Ive retrieved plus one. //public ObservableCollection MyData { get; set; } = new ObservableCollection(); //MyData = new List(); //OK! Its most important properties are: The Data and Total properties of the DataSourceRequest and DataSourceResult match, and allow easy value assignment: ToDataSourceResultAsync is the awaitable (asynchronous) alternative of ToDataSourceResult. If you provide all the Data to the Grid, the component will perform the operations for you. Retrieving Data "As You Need It" with the Telerik UI for Blazor DataGrid, .NET Basics: ORM (Object Relational Mapping), Whats New in R3 2022 With Telerik UI Web Components, When there is so much data that retrieving it all would result in unacceptably long start-up times, When users typically find what theyre looking for in the first few pages that the grid displays (these first two scenarios overlap). The exact number depends on the component's PageSize parameter. When performing an update two events will fire, such as OnCreate and then OnRead to reload the grid data - which makes sense. To refresh the component data programmatically, call this method. I also need to specify how many items Ill fetch (Im holding that in a field called fetchSize). Supported file types: PNG, JPG, JPEG, ZIP, RAR, TXT. First, I need a collection to hold all the data that Ive already fetched (Im calling that collection empData). All Telerik .NET tools and Kendo UI JavaScript components in one package. Progress, Telerik, Ipswitch, Chef, Kemp, Flowmon and certain product names used herein are trademarks or registered trademarks of Progress Software Corporation and/or one of its subsidiaries or affiliates in the U.S. and/or other countries. Copyright 2022 Progress Software Corporation and/or its subsidiaries or affiliates. The first step in setting up the grid for as you need it retrieval is to tie the to some field declared as a List, tied to the object type youre displaying (in my case, Ill be displaying Employee objects). For example, the Grid handler receives GridReadEventArgs. Based on either your previous activity on our websites or our ongoing relationship, we will keep you updated on our products, solutions, services, company news and events. ADMIN NOTE: The goal is to expose a method like args.Request.ToODataString() for the grid OnRead event , so you can pass this on to a service so it knows the grid state (page size, current page, filtering,..). ObservableCollection: System.StackOverflowException! If I do need more data, I retrieve it into a collection called fetchedData and append that to the end of my already fetched collection: If you look closely, you can see that I actually fetch one more item than I need by passing fetchSize + 1 as the second parameter to GetMoreData. To enable filtering, set the grid's FilterMode property to one of the following values: Telerik.Blazor.GridFilterMode.FilterRow - a row of filter options is rendered below the column headers Telerik.Blazor.GridFilterMode.FilterMenu - the column headers render a button that shows a popup with filtering options Use the System.Text.Json serializer. You can perform all data operations yourself (e.g. The Blazor Grid supports CRUD operations and validation. Data Operations The example builds on top of the InCell Edit Mode, and stores metadata and copies of the original Grid items. By default, the Telerik DataGrid for Blazor is designed to work with a collection that implements the IList interface (or either of the interfaces it inherits from: ICollection and IEnumerable) and holds all the data to be displayed. When a component fires OnRead, it expects to receive only the data items to render. Im doing that to determine if Ive reached the end of my data sourceIm checking to see if theres at least one more item to support the user paging forward again. Tickets cost 2 and the journey takes 8 min. Until you expand a group, its child items are not counted and shown in the Total count for the purposes of paging. Please try comparing against it to see what is the difference causing the problem (make sure that you are using the Skip parameter of the data source request when using virtualization): If I am missing something from the scenario, please modify this sample to showcase the problem so I can review the issue. Copyright 2022 Progress Software Corporation and/or its subsidiaries or affiliates. Use async Task and not async void. Marin Bratanov Peter also writes courses and teaches for Learning Tree International. The PageSize of that request is set to 0 so the Grid gets all items for that group. To make the Grid fire OnRead, execute its SetState method Make the grid call OnRead by using its state Edit Preview Grid Data cannot be serialized when using OnRead with LoadGroupsOnDemand. When using row virtualization with a Grid, a DropDownList, a MultiSelect, etc, the OnRead is called for every scroll event, regardless of whether the component _actually_ needs to fetch new data or not. Telerik and Kendo UI are part of Progress product portfolio. When that happens, Ill also set my EOF field to prevent going back to the data source once Ive retrieved all the data. EDIT IN TELERIK REPL. Now enhanced with: New to Telerik UI for Blazor? //List: No update. This approach would make the need to preserve the . For details about server operations, see below. The OnRead event will fire every time you expand a group to get all items for that group. However, once Ive determined that Ive exhausted my data source, Ill give up the pretense and set the TotalCount property to the count of my already fetched collection. If you need to send more files or some confidential data, you can also open a private support ticket from your account. The OnRead method is called when the grid is first displayed, whenever the user pages forward or backward, and whenever the grid is updated. You can also ask us not to pass your Personal Information to third parties here: Do Not Sell My Info. I have two reasons for that, the first being that, as youll see, it simplifies my code. All Rights Reserved. I see the issues in the comment fields. This appears to be documented behavior, but it also seems to me like this is something that the component should be handling. About Sotheby's International Realty Affiliates LLC. Progress, Telerik, Ipswitch, Chef, Kemp, Flowmon and certain product names used herein are trademarks or registered trademarks of Progress Software Corporation and/or one of its subsidiaries or affiliates in the U.S. and/or other countries. This page explains how to enable editing, use the relevant events and command buttons. I will add this info to the docs . Regards, Marin Bratanov Progress Telerik This section contains the following examples: This example shows the basics of enabling the group load on demand - setting LoadGroupsOnDemand="true". default. Telerik and Kendo UI are part of Progress product portfolio. (Total attached files size should be smaller than, Progress Telerik UI for Blazor Feedback Portal. The grid component lets you load the data for each individual group on demand, instead of having it always present. You have the right to request deletion of your Personal Information at any time. The DataGrid in Telerik UI for Blazor's lifecycle events makes it easy to both simplify and centralize functionality that it would otherwise require more complex code spread across multiple events to implement.. "/> The workaround is to assign a new List or ObservableCollection instead of using .Clear(). The exception is -. CUD Events - events related to Creating, Updating and Deleting items Read Event - event related to obtaining data Other Events - other events the grid provides State Events Column Events Command Button Click Export Events SelectedItemsChanged All Telerik .NET tools and Kendo UI JavaScript components in one package. Change Theme. Other properties are discussed in component-specific articles. If there is grouping and the grid needs a list of groups, the GroupPaging parameter of its DataSourceRequest will be set to true. This example shows how you can combine the virtual row scrolling feature with loading group data on demand through a remote service (mocked by a static class in this example so you can run it easily), and how to set the initial state of the grid to have grouping by default. All data operations are already applied (sorting, filtering, etc.). Your first step in the OnRead method is to determine the number of items you have to skip over to get the first item on the new page. On the first call to OnRead I check to see the last Grid state that was stored Copyright 2022 Progress Software Corporation and/or its subsidiaries or affiliates.
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