A Flexible View Control for XPages Part 8 – Putting the 'Flex' in Flexible

Thus far, all of my demonstrations of the Flexible View Control have been centered around starting from scratch and integrating the view control into a mostly blank page, aside from a basic Bootstrap layout. Even the basic Bootstrap layout I’ve been using contains some very important elements that are integral to the control sizing properly, whether you are starting with a blank page or trying to integrate into an existing application.

Enter Flexbox

For years I read about Flexbox and how it can simplify the layout of pages and I always managed to push learning it to the back burner. Once I did all I could think is WHY DIDN’T I LEARN THIS SOONER?!?!? Prior to that, I probably did an embarrassing amount of dynamic element sizing with JavaScript. I can’t stress this enough … Flexbox has fundamentally changed how I approach application layout.

So what exactly is Flexbox?

The Flexbox Layout (Flexible Box) module (a W3C Candidate Recommendation as of October 2017) aims at providing a more efficient way to lay out, align and distribute space among items in a container, even when their size is unknown and/or dynamic (thus the word “flex”).

from css-tricks.com

An important concept to understand is flexible containers are not an “all-in” or “all-out” proposition. You can mix flexed elements with non-flexed elements on the same page, depending on what you’re trying to accomplish.

DataTables and Fixed Headers

Before showing how the FVC integrates Flexbox, a little background. When displaying view data in an application, if the amount of data in the view requires the user to scroll, having fixed headers naturally creates a better user experience. This can be achieved in out-of-the-box DataTables in two ways:

• By adding the parameter ‘scrollY’ to the configuration options with a px value > 0. For example, “scrollY”: “200px”
• By utilizing the DataTables Fixed Header plugin

The pros and cons of each based on my experience are below.

Before using Flexbox for dynamic sizing, the Flexible View Control used the scrollY method to define an initial height and then after the table was rendered, the height of the scroll body would be recomputed so that the table would fit into the parent container. This involved a lot of taking measurements of various elements such as the table offset, header height, filter height, info height, etc. and creating a formula to calculate the correct height needed for the scroll body. It worked great but I really wanted a “cleaner” way to layout the table elements… and I found that with Flexbox.

The Flexible View Control and Fixed Header/Footer

The FVC has a parameter showFixedHeader which is set to true by default. When fixed headers are enabled, the control creates the scrollY option parameter for DataTables at runtime. The value is irrelevant .. the purpose is for DataTables to trigger the dom changes needed to make the table body scrollable:

The key elements here are dataTables_scrollHead, dataTables_scrollBody, and ffDefault. The first two are created by DataTables at initialization. The third, ffDefault is created by the FVC.

Now that we know what the elements are, we need to get them to “flex” by overriding their default styling. The snippet below displays the CSS from the FVC that allows us to accomplish that.

/********************************
 DataTables overrides 
*********************************/
.dataTables_wrapper {
	flex:1;
	display:flex;
	flex-direction:column;
}
.dataTables_scroll {
	flex:1;
	display:flex;
	flex-direction:column;	
}
.dataTables_scrollBody {
	flex:1;
	flex-basis:auto;	
	flex-basis:0;
}
.dataTables_scrollHead {
	flex:1;
	flex-basis: auto;
	flex-grow: 0;
	position:relative;
}
.dataTables_filter input {
    display: inline;
    width: 250px;
    margin-left: 5px;
}
div.dts {
	display: flex !important;
}
/************************/
FIXED FOOTER
/************************/
.ffDefault {
	flex:1;
	flex-grow:0;
	flex-basis:auto;
	height:35px; /* Not required */
	position:relative;
}

With the CSS above we have the DataTables dom elements configured to flex. But we need to do some more flexin’ to get the layout to flow the way we want. Continuing to work our way up the dom hierarchy, we flex the wrapper that the FVC places around the DataTables dom:

.panelRestViewContainer {
	display:flex;
	flex-direction:column;
	height:auto;
	position:relative;
	flex:1;
}

Remember the ultimate goal

We want our view to fit in the space being provided by the flexed layout without having to hardcode dimensions or compute dimensions dynamically. This requires the top-most flexed container defining its height either through pixels or through the viewport height (vh). The demos being used throughout this series (such as this) use the following dom hierarchy (simplified for illustration):

<body>
	<div class="level0-flex-container">
		<div class="level0-flex-item">
			Navbar
		</div>
		<!-- Flexible View Control -->
		<div class="panelRestViewContainer">

		</div>
	</div>
</body>

body, form {
	/* very important! */
	overflow:hidden;
}
.level0-flex-container {
	display:flex;
	flex-direction:column;	
	height:100vh; /* will fill the window viewport */
}
.level0-flex-item {
	flex:1;
	flex-basis: auto;
	flex-grow: 0; /* this element will size to its content */
	position:relative;
}

What this all means:

• Body and form elements will not scroll
• Which allows for the flex container to fill the viewport
• The navbar, with flex-grow: 0, will only get as tall as its content
• The Flexible View Control, with flex-grow: 1 (through the shorthand flex:1 property) will expand to fill the remaining empty space in the container.

The end result is our view filling the screen with scrollable content, just as we wanted.

More Layout Demos

The demos below illustrate how easy it is to create several different flexible layouts and to add the FVC to XPage layout controls:

1. Starting with a flexible container
2. Adding a header
3. Adding the Flexible View Control
4. Add an action bar
5. Add a footer
6. Add a left-side navigator
7. Add a footer
8. Add a right sidebar
9. FVC with NO fixed header in a flexible layout
10. Adding the Flexible View Control to an Editable Area
11. Adding the Flexible View Control to an Application Layout control