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So now that we have learned about explicit intents, let's turn our focus to

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implicit intents, which is one of the most powerful features in Android.

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Let's just start with an example.

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So let's go to the emulator, and we are going to launch the gallery

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application here, which is basically the tool that you use to view the photos

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that are on your phone.

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So I will click Gallery, and I have a couple of pictures on there already, and

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let's say I choose this photo.

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We can see up here we have this button called Share.

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Well, this allows you to send this photo to somebody else, but there could be

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many applications on your phone that are capable of doing that.

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The first one that comes to mind is a text message.

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The next could be sharing it through Twitter or Facebook or through an email, so

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you can have your application be added to that list of applications that can

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actually handle that type of task, and that's what an implicit intent does.

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So this Gallery application, when I click Share, it's actually activating

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using an implicit intent.

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It's basically saying, "Hey, any applications on the system that are capable of sending data,

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here is an image that I want to send out."

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It will then present the user with a list of options.

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Well, here on the emulator right now, if I click Share, there is only one

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option, which is to send it as a text message. And that's because nobody else on

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the phone, no other applications, have actually registered to be able to handle that intent.

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So one thing before we move forward is you are probably wondering how did I get

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images onto the emulator?

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Well, if we go back to Eclipse and go into DDMS, you will notice one of the

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tools up here is File Explorer, and this gives you an Explorer view of the actual device.

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So if we go into mnt, there we see our sdcard.

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And I have put a couple of photos on here that you have in the exercise files in

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the Assets folder, and all you do is to basically click sdcard and then click

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this button over here, which is Push a file onto the device.

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It then allows you to select any file, and it will upload it to the device.

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Let's go back to the emulator here.

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So again, when the user clicks Share, the Gallery application is sending out

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this intent message.

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So how do we know what the intent message is?

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Well, that's easier to do because will just click it and then go back to

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Eclipse and if we look here in LogCat, we can actually see what was sent out

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when the user hit that.

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And we can see here this Starting Intent, and the intent is

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android.intent.action.SEND, which is an implicit intent.

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We can see that with the actual intent there is a data type of image JPEG.

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So again, the gallery is sending out this intent with the JPEG information for

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any applications that are able to handle it.

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So let's create an application that can handle that implicit intent.

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So I have created a blank project here, just called Implicit_Intents, and I

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haven't done anything with it yet.

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So the first thing I want to do is I want to be able to register with Android

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that I'm able to handle that intent, and we do that in the Android manifest file.

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Now we can see for our one and only activity, which is called Main, we

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already have an intent-filter, but this is the one I described to you in an earlier movie.

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This lets the Android system know which activity to activate when our

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application is launched, and that's using this action main intent filter.

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So we are going to add another intent filter, and I am just going to copy this

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block and paste it down here, so we can have multiple intent filters.

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And this is basically advertising to Android that, hey, we are able to handle

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that intent and that data.

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So we are going to put in here, this is going to be action.SEND.

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Now for category, we haven't really talked about categories here.

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Category is a just a way to give additional information to Android about this intent.

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Traditionally, or in most cases, it's best to just use the DEFAULT category,

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unless you know that there's a different category that you should use.

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We are just going to use DEFAULT here.

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Now the next thing that we need to add is a data tag.

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And this is basically telling Android the type of data that we are able to

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handle with this intent.

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So you can see one of the properties is mimeTYPE, and this we just pass in a

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valid mimeTYPE value, which is image/. And remember we saw that in DDMS. We can

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put explicitly JPEGs here, or we can just put star to say hey, we can handle any

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image types that are on the system.

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Okay, so just by adding that to our manifest file, now when on the phone or on

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the device when the user clicks Share or Send, we are going to be able to

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handle that file type, in addition to the text messaging application, and so on and so forth.

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So when the image is actually sent from the Gallery application, let's go ahead

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and do something just so we can actually display it.

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So I am going to go to my main.xml file, which is my layout.

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I am going to get rid of that TextView, and I am going to go to Images & Media,

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and I am going to put in an ImageView.

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So an ImageView is just that--it's a component that displays an image.

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So I am just going to leave it there at the default location, and now I will

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go into my Java code.

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I am going to go into Main.java.

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First thing I need to do, again, like we've done before, is to get a reference to

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that ImageView component.

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I am going to call it iv, and it's going to be findViewById R.Id.

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There's that imageView.

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Again, we want to cast it to imageView.

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Okay, so now we actually want to set the ImageView to the image that was sent to

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us from the gallery that's actually bundled with the intent.

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So to do that we are going to do iv.setImageURI, which is essentially the

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address to where that image is.

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So to this, we need to go into the intent object itself to pull out that information.

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So we are going to say getIntent().getExtras. And again, we covered this in the

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movie about explicit intents.

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And then, we are going to get--and here we are going to use a constant from the

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intent class called intent.EXTRA_STREAM.

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So basically, in the intent object that's sent to us, we are going to grab out that

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stream of information, which is actually a URI to where that image file is.

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Now one thing, we have a quick fix here, we just need to cast that argument to a URI.

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Now remember, we are not doing any checking here that's basically when we come

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in, if we launch this application not through the gallery, we are going to want

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to check for that, but in this case we are not going to worry about it.

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So we are going to run this, and let's actually go to the emulator, wait for our

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application to launch up, and you can see we have an exception.

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Now, this is actually expected because there is no intent when this was just

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launched, because the system just launched it.

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In a real-world case, you are going to want to be able to handle your

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application launching without that intent information.

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But for now, we are not going to worry about it.

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Now, I am going to go back to my image.

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There it is. And now I am going to click Share, and now you can see instead of

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going right to the messaging application, we have an option.

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We can share the pictures via my application that I created called Implicit

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Intents, or use messaging.

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Well, I am going to use Implicit Intents, which is our application, and now you

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can see our application is displaying that photo.

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So again, you can now understand the real power of Android. Whereas all

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applications run in their own sandbox,

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we are actually able to share data, to activate each other's components.

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We just have to set in the manifest file that we are capable of handling different intents.

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AndroidCode.ir
Subtitle by : Mojtaba Haddadi