kb(Grid): prevent checkbox column click (#3027)

* kb(Grid): prevent checkbox column click

* kb(Grid): add PR review suggestions

Author: IvanDanchev

knowledge-base/grid-checkbox-column-prevent-click.md

@@ -0,0 +1,128 @@
+---
+title: Grid CheckBox column prevent accidental click
+description: How to prevent an accidental click in the CheckBox column of the Grid
+type: how-to
+page_title: Grid CheckBox column prevent accidental click
+slug: grid-kb-checkbox-column-prevent-click
+position: 
+tags: grid, checkbox, prevent, click, deselection 
+res_type: kb
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>Grid for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+
+## Description
+
+An accidental click outside the checkbox in the Grid's CheckBox column deselects the currently selected rows. How to prevent that from happening and ensure that only a click on the checkbox deselects the respective row?
+
+## Solution
+
+You can prevent the click event of the cells in the CheckBox column of the Grid with JavaScript. 
+
+1. Call a JavaScript function in the `OnAfterRenderAsync` method and in the `OnRead` event handler of the Grid.
+2. In the function, attach a `click` event handler to the `td` Html elements in the CheckBox column and prevent the event conditionally
+
+```razor
+@using Telerik.DataSource.Extensions;
+@inject IJSRuntime JS;
+
+<TelerikGrid TItem="@SampleModel"
+             OnRead="@OnGridRead"
+             AutoGenerateColumns="true"
+             Sortable="true"
+             Pageable="true"
+             FilterMode="@GridFilterMode.FilterRow"
+             Height="400px"
+             SelectionMode="@GridSelectionMode.Multiple"
+             SelectedItems="@SelectedRows">
+    <GridColumns>
+        <GridCheckboxColumn SelectAll="true" CheckBoxOnlySelection="false" />
+    </GridColumns>
+</TelerikGrid>
+
+<script suppress-error="BL9992">
+    function handleDeselection() {
+        setTimeout(function() {
+            preventDeselection()
+        }, 300)
+    }
+
+    function preventClickHandler(event) {
+        if (event.target === event.currentTarget) {
+            event.preventDefault();
+            event.stopPropagation();
+        }
+    }
+
+    function preventDeselection() {
+        document.querySelectorAll('.k-grid-content .k-table-row td:first-child').forEach(function(td) {
+            td.addEventListener('click', preventClickHandler, true);
+        });
+    }
+</script>
+
+@code {
+    private List<SampleModel> GridData { get; set; }
+
+    private IEnumerable<SampleModel> SelectedRows { get; set; } = Enumerable.Empty<SampleModel>();
+
+    private string LastOnRead { get; set; }
+
+    protected override void OnInitialized()
+    {
+        GenerateData();
+        SelectedRows = new List<SampleModel>() { GridData.ElementAt(2) };
+
+        base.OnInitialized();
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (firstRender)
+        {
+            await Task.Delay(1);
+            await JS.InvokeVoidAsync("handleDeselection");
+        }
+        await base.OnAfterRenderAsync(firstRender);
+    }
+
+    private async Task OnGridRead(GridReadEventArgs args)
+    {
+        var result = GridData.ToDataSourceResult(args.Request);
+        args.Data = result.Data;
+        args.Total = result.Total;
+
+        var now = DateTime.Now;
+        LastOnRead = now.ToLongTimeString() + "." + now.Millisecond;
+
+        await Task.Delay(1);
+        await JS.InvokeVoidAsync("handleDeselection");
+    }
+
+    private void GenerateData()
+    {
+        GridData = new List<SampleModel>();
+
+        for (int i = 1; i <= 100; i++)
+        {
+            GridData.Add(new SampleModel() { Id = i, Text = $"Item{i}" });
+        }
+    }
+
+    public class SampleModel
+    {
+        public int Id { get; set; }
+        public string Text { get; set; }
+    }
+}
+```