knockoutJS checkbox and textbox working together - binding

Question

I have a checkbox and a textbox (both are enabled and the checkbox starts unchecked [false]).
What I need is the following:
When I write something in the textbox and leave it (loses focus) the
checkbox is checked automatically.
When I write something in the
textbox, remove it and leave it the checkbox should remain
unchecked.
When I write something in the textbox and click the
checkbox, the checkbox is checked now and the data in the textbox is
not cleared.
When I write something in the textbox and click the
checkbox twice, first happens step 3 and then the checkbox is
unchecked and the data in the textbox is cleared.
When I click in the checkbox the checkbox is checked, then I write in the textbox
and uncheck the checkbox, then the data in the textbox is cleared.
What I tried so far is the following code:
//The checked property in the checkbox is binded to
that.BuildingCriteria.IncludeLoadingDocks
that.BuildingCriteria.IncludeLoadingDocks.subscribe(function (newValue) {
if (!that.updatingTextBox && !newValue) {
that.BuildingCriteria.LoadingDocksMin(null);
}
});
//The textbox value is binded to that.BuildingCriteria.LoadingDocksMin
that.BuildingCriteria.LoadingDocksMin.subscribe(function (newValue) {
that.updatingTextBox = true;
that.BuildingCriteria.IncludeLoadingDocks(true);
that.updatingTextBox = false;
});
This works if you try all the steps above, for all of them but then, when you try some of them again stops working for some... specially if you write something in the textbox with the checkbox unchecked and then leave the textbox, it doesn't check the checkbox automatically anymore.
I tried using flags as you can see but I couldn't make it to work on ALL the cases ALWAYS.
I've been working on this for days so if you can help me out soon I'd appreciate it a lot!
Thanks in advance!!

Answer 1

It's near impossible to gave a straight up answer to your question, but from it I feel the closest thing may be to note a few KO features that you may yet need to consider.
The value binding supports a valueUpdate = 'afterkeydown' version, which would allow you to keep your textbox and checkbox in synch real time. This may well remove the need for requirement 3.
The computed observable supports specializing read and write operations, which at times may be clearer than using subscriptions.
You may need to introduce a "grace" period for the checkbox, if you must stick with requirement 3. Just don't allow updating the checkbox too shortly after leaving the textbox. The throttle extender and hasfocus binding can help you with that.
There's a great blogpost on when to use which feature.
In any case, your requirements are a bit hard to understand without the business case, and it might even be that you're experiencing an XY-problem. From your implementation requirements I'd assume functional (not implementation) requirements like this:
There's a textbox to hold the actual order/criterium/name/whatever.
There's a checkbox to indicate such an order/etc is wanted.
This checkbox should be in synch (checked) with whether the user typed some text.
This checkbox should be in synch (unchecked) if the user empties the textbox.
If the user checks the checkbox then
If there was text for the order/etc it should be cleared.
If there was no text a default order/etc should be suggested.
Here's a jsfiddle with a demo of how you could approach these functional requirements. For completeness, here's the relevant code, starting with the View:
<input type="checkbox" data-bind="checked: isChecked" />
<input type="textbox" data-bind="value: someText, valueUpdate: 'afterkeydown', selectSuggestion: someText" />
The custom binding for selecting the "default suggestion text":
var suggestion = "<enter something>";
ko.bindingHandlers.selectSuggestion = {
update: function(element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
var currentText = ko.utils.unwrapObservable(valueAccessor());
if (currentText === suggestion) element.select();
}
};
And the ViewModel:
var ViewModel = function() {
var self = this;
var privateIsChecked = ko.observable(false);
var privateText = ko.observable("");
self.isChecked = ko.computed({
read: privateIsChecked,
write: function(value) {
if (!privateIsChecked() && value && privateText() === "") {
privateText(suggestion);
}
if (privateIsChecked() && !value) {
privateText("");
}
privateIsChecked(value);
}
});
self.someText = ko.computed({
read: privateText,
write: function(value) {
privateIsChecked(value !== "");
privateText(value);
}
});
}
I'm aware that this doesn't directly answer your question, but like I said that's pretty hard to do for us on Stack Overflow, without knowledge of your business case.