How to style Grid cell/row background without using classname generator - formatting

Question

I searched a lot, but every solution was to include some constant CSS class names into the page, and use the Column's ClassNameGenerator to set the proper classname on the cell/row.
Now this might be a good solution when the developer can decide on formatting a cell, however when a user can decide (especially with a script written as cell renderer) how a cell will look like, it is not possible to use the ClassNameGenerator.
So question is, how can I format the cell/row background programmatically, not using any CSS? I can provide custom component as cell value. So it's fine to render a label with icon, or just icon, or a checkbox, however coloring this rendered component is not enough, since this is smaller than the cell itself, making it look really ugly. I need to access the root element of the cell, and color it using getStyle().set("background", "xxxx"). How to achieve this?
Thanks!

Answer 1

You can use a TemplateRenderer.
For example:
Grid<Person> grid = new Grid<>();
grid.setItems(people);
grid.addColumn(TemplateRenderer
.<Person>of("<b>[[item.name]]</b>")
.withProperty("name", Person::getName)
).setHeader("Name");
Checkout this tutorial for more information: https://vaadin.com/docs/v14/flow/components/tutorial-flow-grid

Answer 2

OK, finally I solved. I use a template renderer with a proper template structure. I modified the cell style in a way, that my renderer DIV fills the entire cell (removed any padding/margin from the original cells)
<dom-module id="grid-style" theme-for="vaadin-grid">
<template>
<style>
[part~='cell'] ::slotted(vaadin-grid-cell-content) {
padding: 0px;
height: 100%;
display: flex;
align-items: center;
justify-content: center;
--cellopa: 255;
}
[part~='cell'][aria-selected~="true"] ::slotted(vaadin-grid-cell-content) {
--cellopa: 0;
}
</style>
</template>
</dom-module>
I also added some simple CSS declarations to one of the main CSS:
vaadin-grid-tree-toggle flow-component-renderer {
width: 100%;
height: 100%;
}
vaadin-grid-cell-content flow-component-renderer {
width: 100%;
height: 100%;
flex-grow: 1;
}
This way the rendered DIV fills the whole cell and I can color it's background.
Now the problem comes with the selection, since the selection is not visible any more. For this you find the --cellopa variable set to 255 normally and set to 0 for selected cells.
Now when I define a background-color on the div, I use rgba and I set the alpha to the var(--cellopa) variable, like this for example rgba(255, 0, 0, var(--cellopa))
Now when the row is not selected, the cellopa is 255, so the background is visible, when I select the row the cellopa is set to 0, so the background of the DIV gets transparent, and the row selection color on the row is visible. This is super fast, and changing the selection does not cause any glitch, and also the previous coloring state is restored properly.
I also managed to get around with the treegrid and managed to color even the hierarchy column fully using a special template for the hierarchy column with some padding taking the level into account.