How to build an interactive hierarchical data-grid using custom directives. Shows how to capture keyboard input, navigate the DOM tree with jqLite and display google spreadsheet like selection rectangles.

1. AngularJS
for Interactive Application Behavior
Brent Goldstein
brent@kubilateam.com
Practical Directives

2. Back Story
● Building an app and want rich behavior
○ Don’t limit goals because “it’s a web app”
● Need an interactive Spreadsheet-like Grid
○ Hierarchical data, specialized data entry needs
○ Similarities to Google Sheets, some differences
● Yikes, this seemed daunting at first
○ Hierarchical Data Binding
○ Navigation
○ Complex element/range selection

3. Requirements - (be a product mgr)
● Hierarchical Data Set
o 3 Row Levels - Person, Projects, Tasks
o Columns are calendar weeks
● Navigate and Select like a Spreadsheet
o Move w/ arrows, tab, shift-tab; mouse-click
o Select single cell or range of cells
● Specialized Editing
o Business logic applied to keystrokes before display

4. How to Render Complex Data?
● Resist thinking like an ‘engineer’
● Visual representation must be intuitive
● Even more important that ‘being’ intuitive
→ will someone actually use it?
● Really must pass the dog food test

5. Digression - Dogfooding?
● OK, this is one of many overused tech industry terms
● Seems to put a rather unappetizing spin on one of the
MOST IMPORTANT practices in application design
● It does not matter what you think or say, or what others
think or say about using your app
● The application must draw you in (yes, YOU)
● Otherwise, it’s just neat tech, and neat is not a product

6. Grid Hierarchy Rendering
● Go “Flat” -- flat visual data modeling that is
● Basically, de-normalize where it makes sense
→ use grouping to organize
● Greatly simplifies UI construction and interpretation
● Still possible to “drill down”, but using filters and
selection to show more/fewer rows
● Avoid “nested grids”; hard to render, hard to read

7. So how to build it?
<div grid-editor>
<div class=’grid-person’>
div div div div div div ….. div
…..
…..
<div>
…..
<div>
<div class=’grid-person’>
<div>
- Custom Directive “grid-editor” provides special behaviors
- Grid-Editor looks for child DOM elements with special classes
Note, grid constructed from divs, not tables, to support custom layout

8. DOM Location and Navigation
Let’s consider one use case, Find the Next cell to the RIGHT
<div grid-editor>
<div>
<div class=’grid-person’>
<div>
...
<div class=’grid-project’>
<div>
<div class=’grid-project’>
<div>
1) At last cell, but not last in row
2) At last cell in row
3) At last cell/row in grid-project
Actually requires handling several sub-cases...

9. Getting down to Business -- jqLite
Assuming we know the selected cell, we can find the next like this:
<div grid-editor>
<div class=’grid-person’>
<div class=’grid-project’>
1) At last cell, but not last in row
col=’1’ col=’2’ col=’3’ col=’4’
col=’5’ ...
2) At last cell in row
Case 1) Look for next sibling element, use attribute to be selective
var newElement = currEle.next(‘[col]’);
Case 2) Look for the FIRST element in the NEXT row (requires some maneuvering)
var newElement = currEle.closest(‘grid-project’).next(‘grid-project’).find(‘.first’)
Similar ‘traverse up, look for next’ can be applied to higher levels in hierarchy
col=’6’
applied applied to first cell div: class=’first’ to every cell div: class=’cell’

10. Going down, same column, new row
What about other cases, like the down arrow key?
Need the next row, but column needs to remain the same. Now that’s why the
“col=n” attribute is useful….
Look for next sibling row, use attribute to find the correct column
var newElement = currEle.closest(‘grid-project’).next(‘grid-project’)
.find(‘.cell[col=’ + currEle.attr(‘col’) + ‘]’);
<div grid-editor>
<div class=’grid-person’>
<div class=’grid-project’>
col=’1’ col=’2’ col=’3’ col=’4’
col=’5’ col=’6’
col=’4’

11. How to capture the arrow keys?
Can be useful to step outside of Angular for event handling
element.bind('keydown keypress', function (e){
if(!scope.editActive) return; // track the editing state
var navArrow = function(e){
var arrowKeys = { 37:'left', 38:'up', 39:'right', 40:'down' };
return arrowKeys[e.which];
};
var navTab = function(e){ // tab key
return (e.which === 9) ? (e.shiftKey?"left":"right") : null;
};
var doNav = navFromArrow(e) || navFromTab(e);
if(doNav){
e.preventDefault(); // prevent the browser default action
theFunctionThatNavigatesToNextCell(doNav)
}
};
The ‘element’ above could be the $document root, or a sub-document,
depending on the desired behavior. If a sub-doc, the keys will only be
captured when that element or children have focus

12. Rendering the Selection Band
To indicate selected cell, a “rectangle select band”
is typically used to surround the cells
How to accomplish this in DOM?
A couple of options:
1) Identify and alter the display the underlying
DIVs
2) Add new elements that Overlay the native grid

13. Draw band using actual grid cells?
Altering the display of underlying cells can be tricky.
How to actually make the highlight band?
- Alter the div/span border(s)
Not ideal. Positioning is limited to element border
Also harder to make a multi-cell rectangle

14. Overlay Rendering
What about creating a new element/set of
elements that display ON TOP of the grid?
Let’s timewarp back to 1998 when graphics
were rendered into framebuffers.
Remember the Overlay Framebuffer?
Let’s apply the same logical concept

15. The Magic Select Rectangle Band
How to render the select rectangle in DOM?
We’ll construct with separate banding elements for max control
It will simplify hover/select options since we can know exactly which side of the band is
under the mouse
Top DIV
Bottom DIV
Left Div
Right Div
With this approach we can also add other visual elements, like a cursor select target for
dragging, etc.

16. Dynamic Element Creation
The select band is managed by the GridEditor Directive:
- Create: When the directive is instantiated
- Move: When the arrow/tab keys are captured
- Grow/Shrink: Based on shift-click
This function is called inside the directive link() function to instantiate the band elements:
var _installBand = function(){
var html =
"<div id='magic-square'>"+
"<div class='band-horiz top'></div>" +
"<div class='band-horiz bottom'></div>"+
"<div class='band-vert left'></div>"+
"<div class='band-vert right'></div>" +
"<div class='band-grabbox'></div>" +
"</div>";
_band = angular.element(html); // this creates the dom element
_gridEditorElement.prepend(_band); // attach to directive element
return _band; // to adjust properties and location later
};

17. Dynamically alter DOM properties
Properties are updated to adjust the rectangle band size
when needed
Note, _unitWidth is already set with the pixel width of a single cell
var _setBandWidth = function(){
var rangeWidth = _range(); // gets the desired #cells to cover
// update the top/bottom horizontal div widths
_band.children(".band-horiz").width((_unitWidth-1) * rangeWidth);
// update the right vertical div position
var rightVert = _magicSquare.children(".band-vert.right");
var posLeft = (_unitWidth-1) * rangeWidth -1;
rightVert.css({left: posLeft});
};

18. Let’s take a look - Initial View
Top-level view, summary data
User sees this view when page is loaded
● Threshold coloring (red means too much)
● Click on row to expand
● Expand All/Collapse All buttons

19. Let’s take a look - Expanded View
Details for each person visible when expanded
● Project-task rows at same indent level
● Grouping by project
● Optional project sub-total rows

20. Let’s take a look - Editing
Behaviors to streamline complex editing needs
● Single Select and Range select
● Smart Navigation across projects/people
● Shortcut keys for pre-defined operations

21. Coding tidbit - $emit for messaging
Both $scope.$broadcast() and $scope.$emit() can be used
to communicate between directives and controllers
What’s the difference? Well, direction:
$emit goes UP, $broadcast goes DOWN
As a result, $emit is more efficient bubbling only to parents
$broadcast fans out to all child scopes
Maybe you really need $broadcast... but often not
$emit can be applied in a message-bus pattern to achieve
efficient dedicated communication across an app

22. $emit for messaging
Message bus approach can often replace $broadcast
1) Bubble Up 2) Message Bus
Higher level controller
or directive
$scope.$on(‘hello.world’,
function(event){//dosomething));
$scope.$emit(‘hello.world’);
Originating Controller or
Directive
RootScope actiing as
message Bus
$rootScope.$on(‘hello.world’,
function(event){//dosomething));
$rootScope.$emit(‘hello.world’);
Originating Controller or
Directive
Listening Directive or
Controller

23. thanks!
contact: brent@kubilateam.com