Using Custom Conditional Statements in Titanium Alloy Views

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One of the many great features of Alloy (and I’ll be covering more in an upcoming post) is how it separates the business logic of an app and the user interface. You use XML views and TSS files to define the elements and styling of your views, and controllers contain the JavaScript to make everything work.

One challenge that comes up from time to time is how to hide and show content in a view based on a condition within the app – for example showing or hiding content when a view opens based on wether the user has logged in or not.

Here’s a simple example that shows a View that has two visual states — one where it shows the user is logged in and one when they’re not.

(Worth mentioning that in this example, there’s some additional TSS that’s used allowing views / windows to be vertical layout, and the View tag has been set to have a default height and width of Ti.UI.SIZE)

<Alloy>
        <Window>
            <View class="container indent">
                <View id="notLoggedIn" class="vertical">
                     <Label                                                                        							text="Not logged in"                        
                    />   
                </View>
                <View id="loggedIn" class="vertical">
                    <Label                                                                        							text="Logged in"                        
                    />                    
                </View>
            </View>
        </Window>
</Alloy>


In this example, I might typically handle hiding and showing content using some JavaScript code in the controller, based on calling a method in the alloy.js file called Alloy.Globals.isLoggedIn:

if (Alloy.Globals.isLoggedIn()) {
    $.loggedIn.show();
    $.notLoggedIn.hide();
} else {
    $.loggedIn.show();
    $.notLoggedIn.hide();
}


This kind of works in terms of the showing and hiding of elements, but the problem is that both views were rendered to the view when it opened, and then the visibility changed. This means that if the user isn’t logged in, there’s a big white space above the non-logged-in view.

Not ideal.

The “classic” way of dealing with this was to not use show/hide at all but to change the heights:

if (Alloy.Globals.isLoggedIn()) {
    $.loggedIn.setHeight(Ti.UI.SIZE);
    $.notLoggedIn.setHeight(0);
} else {
    $.loggedIn.setHeight(0);
    $.notLoggedIn.setHeight(Ti.UI.SIZE);
}


This works, but it’s messy. We’re also assuming that the default setting of each view should be Ti.UI.SIZE which isn’t ideal.

Thankfully, there’s a simple to do this with Alloy using IF attributes within the XML View.

Let’s update our View XML:

<Alloy>
        <Window>
            <View class="container indent">
                <View if="Alloy.Globals.isLoggedIn()" id="notLoggedIn" class="vertical">
                     <Label                                                                        							text="Not logged in"                        
                    />   
                </View>
                <View if="!Alloy.Globals.isLoggedIn()" id="loggedIn" class="vertical">
                    <Label                                                                        							text="Logged in"                        
                    />                    
                </View>
            </View>
        </Window>
</Alloy>


You’ll notice a couple of things — I’ve added an IF attribute to the View element that calls a method called Alloy.Globals.isLoggedIn in alloy.js. You’ll also notice the second View if attribute prefixes the method with ! because we want that to show if the method returns false.

When creating the View, Alloy is checking the method and if it returns true, the first view is rendered, and if false, the second view. What’s nice about this is that it only renders one or the other — so there’s no white space anymore.

Similarly, you can use IF attributes in TSS definitions to change the way elements display based on custom properties or methods, for example:

"#info[if=Alloy.Globals.isIos7Plus]": {
    font: { 
			textStyle : Ti.UI.TEXT_STYLE_FOOTNOTE 
			 }
},
"#title[if=Alloy.Globals.isIos7Plus]": {
    top: "25dp",
    font: { 
			textStyle : Ti.UI.TEXT_STYLE_HEADLINE 
			 }
},
"#content[if=Alloy.Globals.isIos7Plus]": {
   font: {
			textStyle : Ti.UI.TEXT_STYLE_CAPTION1 
			}
},
"ScrollView[if=Alloy.Globals.iPhoneTall]": {
	height: "500dp"
}


You can even use conditional queries by defining custom methods in your models in Alloy, and then render elements based on those methods when data-binding. In this example, a comment row is only displayed if a model has a method called shouldShowCommentRow which returns true:

<Alloy>
	<TableViewRow
    id="commentRow"
    hasChild="false"
    if="$model.shouldShowCommentRow()"
    onClick="onSelectComment">
    <Label id="commentPlaceholderLabel" class="commentRowPreviewLabel placeholderLabel" text="Ti.App.L('AddComment')" />
    <Label id="commentRowLabel" class="commentRowPreviewLabel" text="{Comment}" />
	</TableViewRow>;
</Alloy>


As you can see, there’s lots of ways to use custom queries within Alloy, to reduce the amount of JavaScript you need to write and take advantage of these conditions running before any rendering is carried out, providing a smoother app experience.

You can find out more about buy checking out our guide on Custom query styles.

Happy Coding!

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2 Comments

  1. Chrystoffer Kugler Horochovec

    Very useful!
    Tks

  2. Matías Schmid

    +1!!

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