105. Building and Using a Dropdown Directive

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Welcome back to the recipe book.

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We already use ngif and ng4 in this section,

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so we're already using directives.

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But now I want to enhance this project by adding

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our own directive,

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which allows us to open the dropdowns,

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which don't work as of now if you click them.

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They don't work because we didn't import Bootstrap's JavaScript code,

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and I don't want to import this because Angular should be the only thing interacting

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with my DOM.

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But now with the directive knowledge,

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we can create our own directive,

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which will manipulate these buttons.

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I'll add the directive in the shared folder

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and I will name it dropdown.

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directive so the file is named drop down directive dot ts

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of course you could use the cli to create it and

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you could even point to the shared folder in the command to automatically generate

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it in this shared folder i'll do it manually though always

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a good practice and here the name should be drop down directive

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like this and of course we need to add a

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decorator to turn this into a directive

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So it's the add directive decorator,

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which needs to be imported from add angular core.

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And here there is one thing I need to set up.

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On the selector,

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I want to define how I can add my directive.

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And I will use an attribute selector.

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Therefore, I'll enclose the name in square brackets.

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The name now will be app...

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drop down to have a unique name which doesn't accidentally interfere

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with an officially existing attribute name or anything like that.

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Now what should this directive do?

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I want to add some functionality to it which allows us

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to add a certain CSS class to the element it sits

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on once it is clicked.

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So once this element the directive sits on is clicked and remove

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the class once we click again let's say.

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So this is your challenge.

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Try implementing such a method which basically listens to

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clicks and then toggles some property which determines whether some class is attached

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or not.

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And also try implementing some code which dynamically attaches

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a CSS class or not.

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Before you actually start though,

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let's find out which class we need to attach.

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If you go to the recipe detail component here,

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if you attach the open CSS class to the

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div, which holds button group,

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and you go to your application and select the recipe,

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you see now it looks like the dropdown was opened.

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So it's this open CSS class,

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the same for the usage in the header we need to attach.

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So that's your challenge.

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Build a dropdown directive,

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which attaches this class whenever we click on it or removes it once

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we click a second time.

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Let's build this directive together now.

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So as explained,

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I want to toggle it upon clicking this.

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So to listen to a click,

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I should add host listener,

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which is to be imported from Angular core.

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And I want to listen to a click event.

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Then I want to execute toggle open,

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which looks like or sounds like a fitting name because that is what I want to do.

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I want to toggle whether this should be opened or not.

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Well, then I will add is open directive,

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which I'll set to false initially.

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And in my host listener,

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I'll simply set open or is open to,

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well,

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what it is currently not.

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So if is open was true,

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it will now be set to false and the other way around.

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So with that,

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I'm toggling that property.

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Now to dynamically attach or detach a

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CSS class depending on this,

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all I have to do is I'll add host binding,

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which needs to be imported from Angular core and allows us to

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bind to properties of the element the directive is placed

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on.

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And here I want to bind to the class

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property of that component,

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of that element.

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Class simply is an array of all the classes.

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And here it's all about this open class.

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As you learned,

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that's the CSS class we need to attach dynamically or detach.

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And now the rest will be handled by Angular.

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Since I bind to isOpen,

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this will not be attached initially.

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whenever is open switches to true it will be attached and whenever

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it switches to false it will be removed and that's our entire directive

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now to be able to use it i need to go to app module

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and add it here add the drop down directive and

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add the import pointing to the shared folder and with

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that imported now

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I can use it.

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I can use it in the detail component.

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Here,

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I have to use it on the div or on the element where open should

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be attached to in the end.

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So in this case,

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the div with the button group class.

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And here,

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I'll add my own app dropdown directive without squared brackets,

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without assigning any value because,

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well,

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I don't need to configure anything on this directive.

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And now in the header,

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Here the place where I need to add it is this list item with the class

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of dropdown.

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Here this is what will actually need the open class to show something.

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With that in place and ng -surf still running,

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let's save this and view this in our application and see if this works

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the way it should.

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Let's test it in the header.

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Looks pretty good.

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We close it by clicking again.

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And here on our recipe,

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That looks awesome too.

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So that's working exactly the way I want it to work.

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And with that in place,

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that already is everything I wanted to build.

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So a relatively short recipe book section here.

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Now we can move on to services,

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a very powerful tool.

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And then we will add services in this app here to greatly

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enhance it and fix some things which we had to do kind

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of complicated thus far.

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We'll also add some new features.

105. Building and Using a Dropdown Directive

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