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In this video we create a Cache Manifest which will allow our application to be fully cached on a device so it can be used offline.
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[Jim Hoskins] So now we have a pretty cool mobile application
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that can save Notes, save locations to Notes,
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get you a list of your Nearest Notes, and so on.
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Now, what's really going to be great is if we can use this offline.
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Right now, it is always requesting the latest code from the server,
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but if we're not connected to the server, it would be nice if the application still worked.
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After all, it doesn't need a server to store data,
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so if I'm offline, why should the application not be available?
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Let's see what would happen if I turn off Web Sharing,
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which is right now what's controlling my Apache web server in development.
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So we turn that off and I refresh,
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we cannot connect to localhost because our web server is not running.
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What I want to happen is I want to be able to access my application.
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So I'm going to turn our server back on--
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it will just take a minute to fire up--
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and if I refresh, we should get our application back like that.
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So the way we can do this is utilizing HTML5 offline application storage
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and what this is is we will simply create a manifest file
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telling the web browser about all the assets needed to run this application.
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Then, when it gets them, it will cache them away,
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and if it's unable to reach the server, it can use those cached files.
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Now, the best online documentation I found from this
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is from the Dive Into HTML5 book.diveintohtml5.org/offline.html
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Now, it's a huge subject--this goes into how everything works--
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and the best way to manage your cache, including a few gotchas
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that you really, really want to take care of.
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So first, let's go ahead and try to create our cache manifest file.
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Now to do that, we will create a new file in our directory called cache.manifest.
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Now, how this works is it will start off with the lines CACHE MANIFEST
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and any lines that begin with a # will be a comment
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so what we're going to do is we're going to comment of #Cache Manifest rev: 1.
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The reason I'm giving a revision number here is because the application will only try to fetch
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the newest contents if the cache manifest has changed.
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Now, this is important because when we're developing or deploying new information,
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we may want to tell the browser to recache all the assets.
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However, the actual values in our cache manifest file might not change.
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So one way we can change the file is to change a comment every time we update our files.
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So then, the way it works is we can have a CACHE line with a colon
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and every file we list here--like index.html, css/main.css--
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every one of these files, when the page loads, will be cached away.
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Now, there's always a different header we can give of NETWORK:
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The section under this will never be cached,
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and this is important, especially since we're using Google Maps,
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which we can't cache and we wouldn't want to have it actually try to cache.
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So what we will do is we'll say you always need to use a network
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for the Google Maps.
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So the tricky part here is we need to actually get all of our files
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into this cache section.
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Now, one way we can do this is to use the Terminal
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and use a little bit of text editor magic to try to streamline this for us.
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We could go through each of our files, but since we have several JavaScript files
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and several CSS files and icons included with jqjQuery Mobile,
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it's going to be a long process to manually type in
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each and every file associated with our project.
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So what we can do is from our web directory here,
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we could type in $ls for listing - l for the long form
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and capital R for recursive, and what this will do
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is it will print out all of our files in all of the subdirectories
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of this current directory.
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We're going to go ahead and edit that output in order to create our cache.manifest file.
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So here we can see each of our different directories here,
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and what I'm going to do is I'm just going to try to copy this all out
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and I'm just going to paste it into our cache section here
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and we get the output of all of our files in here.
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So now we just need to go ahead and clean this up.
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Now, depending on how good you are with macros and stuff,
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you can probably do this a lot faster,
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but one thing I like about TextMate is if you hold down the Alt button,
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it takes you into a special Block Select mode
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where you can select certain columns along certain lines
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instead of doing a normal linear select.
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So by holding down Alt, my cursor changes into a cross here
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and I can just drag from here all the way to this column
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because I want to get rid of all of this,
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and with this all selected, I can simply hit delete and it's gone.
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Now, on this top level, there's really only one file I need.
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I don't want to cache the manifest itself.
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I don't want to cache the directories--we'll do that in a moment--
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of css and js.
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And this total header here I just want to remove.
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So we have our index.html.
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Obviously, for that section, it would have probably just been faster
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to type index.html, but let's just keep on moving along.
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So in our CSS directory, we have four files.
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In our CSS directory we have three files and a directory.
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We don't want this directory because we'll be handling each file in the directory separately--
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I don't want this header line here--
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and by using our block select mode,
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I will delete all of that.
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I do need to prefix css/ to each of these lines.
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I can go ahead and remove this line and replace it with #CSS.
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So to add css/ to the beginning here,
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what I'll do is hold down Alt to go back to block select mode
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and select a column before the first character in here.
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You can barely see it, but there is a selection before each line here
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and when you have a block selection like that when you start typing,
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it will type simultaneously on all lines.
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So to add CSS, I'll just type in css/ and we have changed all those files at once.
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So this is for css/images, so let's clear that header line.
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Let's use block select.
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We have that all selected.
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If I hit delete, I've lost my selection, but I can grab that again
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by just holding Alt and drawing down the left column here.
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I'll add in css/images/
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and I can change this into a comment.
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I'll do the same for js; remove this header
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and I can do this all in one go by just selecting it all,
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and instead of hitting delete, I could just type in js/ and we'll go ahead and into a header as well
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and that is all of our files.
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So now we've created a cache.manifest file
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and this should work for us.
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Now we need to integrate it into our application
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to tell the browser that we have this cache manifest file
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and it should be using it.
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Now, there's a couple of things you need to do to your server
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or you may need to do to your server in order to have cache.manifest work.
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One is that a .manifest file should always be served
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with the mime type of text /cache-manifest
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so what we need to do is tell our server that any .manifest file
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should be served with that mime type.
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The server may already be configured for this
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but if it's not, we need to go ahead and add a line to our Apache configuration file
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or whatever server configuration you have set up.
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I'm going to show you how to do it on a Mac
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using the default Apache install.
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Going to our Terminal here, what I could is open up our configuration
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by typing in $mate /etc/apache2/mime.types
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and here we can see the list of all the mime types we have here.
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And so what I'm going to do is at the bottom here,
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we'll add our own of text/cache-manifest
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and we'll add some space here and we'll say always serve that
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when we have a manifest file.
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Now, when you save this out, since it is a privileged file,
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you may need to give your password in order to save it out
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and then you'll need to restart your server.
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So let's actually test out if we are getting the cache manifest file served correctly,
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so we'll go to cache.manifest.
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We can see it is serving
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and we can actually see it's interpreting this resource of the document
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but it was actually served with text/cache-manifest,
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which is exactly what we want.
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On this page it shows you can also use an AddType declaration
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anywhere in your configuration, or you can do it in the mime.types folder
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like we did before.
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One last thing you want to do--especially while in development--is to make sure
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that the server is not going to cache the cache-manifest itself.
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Otherwise, it becomes very, very, very difficult
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to get past the cache.
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One way you can do this is to create a .ht access file for your Apache server
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and set ExpiresActive On and ExpiresDefault to "access"
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so it'll clear the cache every time it tries to access the file.
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So we can create a new .htaccess file with this information on it
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and I'm going to go ahead and just restart the server.
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You may not need to, but I like to do that any time I change anything.
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Let's go back to localhost here, and the cache manifest will not be in effect yet
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because we have not included it in the index.html.
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So if we refresh, we're not getting any weird server errors,
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which is always a good sign,
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and the last thing we want to do is in our index.html in the HTML tag,
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we want to define where the manifest is for this application.
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So we'll go back to our browser,
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open index.html,
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In this HTML tag, we will add manifest= and then location of it of /cache.manifest.
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Save it out and let's take a look at it in the browser.
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So here we can see a lot of debug information here.
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We can see the application was found, it's downloading all of these different files,
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and it's very important to keep track of this.
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If you have a missing file or file that it can't find,
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it will actually abort mid-process here and nothing will be cached.
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So you need to always make sure that your cache is correct,
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pointing to files that it can find
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because a single 404 will break the whole cache.
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Now, if we refresh, it should still work.
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We still have access to all of our localStorage here.
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Now, let's go into our server here, turn this off,
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and let's refresh.
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We refreshed and it is still working just fine.
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And add New Note with Some Text.
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We can even add our location here and save it out.
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You can see our New Note works just fine
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and this is all with our Apache server turned off.
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We can refresh as much as we'd like
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and we will always get this because the browser has all of the files it needs
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to serve this application.
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Any time you change any of your files,
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you would want to update the cache.manifest to have an updated revision number
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just so you can change the cache so the browser will get all of the new files that you need.
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I usually like to do all the caching stuff right at the end of my application
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because it's easier to develop with the cache off,
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but you definitely want to do some extensive testing with your cache
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to make sure it works.
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Now I'm going to turn my server on for one last check.
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I'm going to turn on my server.
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So if we refresh it, it looks like our app is working,
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and now in the act of refreshing it, it should be caching all of the files.
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So if we turn off the server once again and refresh--
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cool, it looks like we get the entire application working
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even though our server is turned off.
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So now we have an offline Geolocation-aware localStorage-based mobile application.
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And now our note-taking application has the ability to be run offline
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using the HTML5 application cache
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and we can add location data to our Notes.
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The next step would be to actually take your device out into the real world
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and test it using real location data.
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