Transition Items within a List with React Transition Group

Instructor: [00:00] In this example, we have a list of ingredients. When an ingredient is pressed, it's toggled from the list of favorites. The way this is put together is that we have a list of items at the top of our component. These are the ingredients. Favorites is initialized to an empty array and it's stateful.

[00:24] We have a toggle in favorites method, which will remove or add depending on its presence in the favorites array and then set the state accordingly. Down here, we have the render method in which we map over the initial items, and display list element for each one, and lastly the favorite section which appears on the right.

[00:56] In its current state, the favorites are added and removed immediately. Let's add a transition for each of the favorites, so that they appear and leave smoothly. To do this, we're going to need two components from ReactTransitionGroup, CSS transition, and transition-group.

[01:17] CSS transition will be applied to each of the favorites, and transition-group will be used as the container for individual CSS transitions. Let's use these components inside our render method now. Inside our map of our favorites, we're going to add the CSS transition components.

[01:41] It's going to have a time out of 500 milliseconds. It's going to have fade class name. This will be useful when we add a transition in the CSS. It's going to have the key as currently on our div. Now, we can apply the transition-group components which is going to go in place of the container div.

[02:09] This acts as a wrapper for using multiple CSS transitions inside this map method. Let's save now and see how that affects what we have so far. Now, when a favorite leaves the list, there's a 500 millisecond delay. Now we're ready to write some transitions.

[02:30] Let's head into our index.css, and there were already some style set up for the positioning and the colors of what we have here. Let's add some variables to the top of our file. We're going to add a time out value which is the same as what we have in our index.js.

[02:49] We're going to add list item max-height, because we're going to be transitioning the max-height of each of the favorites, and it's just convenient to be able to have it as a variable should we want to change it.

[03:02] Now at the bottom, we're going to start writing some styles for a fade transition. As fade is the class name that we supplied to CSS transition. We can use fade-enter, fade-enter-active, fade-exit, and fade-exit-active.

[03:27] We're going to start and finish with a max-height and opacity of zero. We're going to transition to a max-height of the variable that we set at top and an opacity of one. The favorite is going to transition its max-height and its opacity. Fade-enter-active and fade-exit-active, a class name's applied on the next take after fade-enter and fade-exit.

[04:03] That means we can target these with the transition. We're going to say transition all by the time out on fade-enter-active and fade-exit-active. Our CSS is looking good now. Let's save and refresh, and see what we end up with.

[04:25] Now, when items are added, they are faded in. When an item is removed, the item underneath slides up which gives a good indication of which item is leaving and where.