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So in the last lesson, we manage to successfully implement our search bar,
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but now we want to be able to go back to our original list of all of our items.
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For example, when we click on the cross button, right? That's a normal behavior that users have gotten used to
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when they clear the search bar.
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So let's go into our TodoListViewController extension which is the part that deals with our search
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bar methods,
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and let's go and create a new delegate method here.
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And the method that we're going to use is, of course, relating to the search bar.
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And we're going to look for the delegate method that is searchBar textDidChange.
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So this triggers the delegate method when the text inside the searchBar has changed,
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so that means every single letter I type in here is going to trigger this delegate method. But also when
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I go from a whole bunch of text to no text, this delegate method is also going to be triggered.
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Now, I can isolate that particular instance by checking inside this delegate method.
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So whenever there are any changes inside the text of the searchBar, I can see if the 
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searchBar.text.count which looks at the number of characters in the string or the searchBar text is equal
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to zero.
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And because of where this "if" statement exists, it means that text inside the search bar has changed, but
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it has also gone down to zero.
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So when we first load up the app and the search bar has no characters inside, this method, this delegate
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method is not going to trigger because the text has not changed, and it's only when the text is changed
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and it's gone down to zero
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which pretty much describes the time point when I click that cross button
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does this part of the code inside this "if" statement get triggered.
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So inside here, I'm simply going to call loadItems, which if you' remember, have a default request that
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just fetches all of the items from my persistent store,
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just as we had up here in the viewDidLoad.
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So, now if we run our app, and let's try and check it out, let's search for "Save," hit search, and then we're
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going to click the cross button, and you can see that we are now reverted to our original list of items.
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Now, this just one niggling thing. The fact that our keyboard has not dismissed itself and our cursor
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is still flashing in the search bar,
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now how can we get it to go back to the original state where the search bar doesn't have a cursor and
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the keyboard is dismissed?
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So, in order to do that, we need to call upon a method called resign first responder,
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so telling the search bar to stop being the first responder.
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Now, we're going to do it inside here after we call loadItems and we grab a reference to the 
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searchBar that we've got,
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and we're saying resignFirstResponder which notifies this object, i.e., the searchBar that it has been
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asked to relinquish its status as the first responder in its window.
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Now, that sounds pretty dramatic, right?
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It's like, you know, you're being overthrown or something.
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But actually all it refers to is that it should no longer be the thing that is currently selected,
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so no longer have the cursor and also the keyboard should go away because we are no longer editing it
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anymore.
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Basically, go to the background, go to the original state you're in before you are activated.
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Now, whenever you're writing methods to affect the user interface, you tend to want it to tap in the
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foreground.
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Now, if we run the app and have an active session, if I click on the pause button here in the debug console,
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you can see that we can trigger a debug session. And it's at this point that you can see that we've got
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actually multiple threads that are running, but only one of them is the main thread in our queue.
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So for example, if I decided to make a network call to, say, a Firebase database on the main thread, then
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it means that it has to go over the Internet, grab the data back,
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and no matter how long that process takes, it's going to freeze your app until it completes
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which is why we tend to complete those tasks in the background using another thread which means the
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user interface is not going to freeze up
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while we're waiting for that process to complete. And on the background thread, once that process is complete,
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then the data gets delivered back and we can update the user interface using the main thread.
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But in our case, while background task are happening, we need to grab the main queue so that we can dismiss
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our searchBar,
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even if background tasks are still being completed.
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So in order to do that, we have to tap into the dispatchQueue
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and this is the object that manages the execution of work items.
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So it's almost like when you're submitting an application for a visa, right, to an embassy, and you have
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somebody at that embassy who is prioritizing who should be processing your visa.
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So, for example, if you were a diplomat or you paid for, you know, extra fast service, then your passport
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might get sent by the manager to the guy who's, you know, working 24/7 stamping visas, so that your visa
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processing happens immediately.
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However, if you are just, you know, just a standard person trying to get a visa to, you know, somewhere exotic
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for the winter, then you might get shuffled to, you know, the guy who only works one hour a day,
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and they have so many tasks lined up that it might take you a week before you get your visa processed,
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again, and get your passport back.
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So the DispatchQueue is that manager who assigns these projects to different threads.
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And we're going to ask it to grab us the main thread.
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And this is where you should be updating your user interface elements.
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And then we're going to tap into a async method.
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And inside this block of code, we're going to insert our searchBar updating code.
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So whenever you're trying to move code inside Xcode, it's a little bit tricky because it's a matter
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of timing.
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You have to click on it and wait for the arrow to appear and the cursor to disappear before you start
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dragging.
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Now, you can move your code.
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So now we're saying "Ask the DispatchQueue to get the main key, and then run this method on the main queue.
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So, now if I run my app and we hit search, then we get back all the items that has the word "Save." But when
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we dismiss the word "Save," then our keyboard pops away and our cursor disappears from our search bar.
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All because of this line of code being run in the foreground.
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Now, in the next lesson, we're going to take Core Data much further, and we're going to learn about one
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of its main features which is establishing relationships or what we might call graphs inside Core Data.
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And we're going to turn our simple to-do list into one that's more like a real-life to-do list
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by having a separate to-do list for various categories.
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So for all of that and more, I'll see you on the next lesson.