Sometimes we start a second activity with the intention of getting some data to use

in the original activity.

We need to specify this when we start the activity by using a different method,

start activity for result.

So back here., let's delete this line where we are starting the activity,

and instead call it startActivityForResult.

There we go.

The first parameter like before is our intent, but

now we also need to include a request code.

Like with extras, it's a good practice to define some reasonable constants.

So let's call this REQUEST_FAVORITE and then define it at the top of our class.

So I'm going to scroll back up to the top in here where we have our static strings.

Let's do public static final and in this case it's an int or

request code has to be an int and we called it REQUEST_FAVORITE and

we can set this to really anything we want let's just set it to zero.

We'll just count up from different requests values

are useful when we request different types of information from an activity.

All right so now we're expecting a result to come back here to main activity.

How will we handle it?

Using start activity for result requires that we implement another method

in the activity to handle the result.

Let's scroll down all the way to the bottom of our class and have it.

I'm gonna add a few lines here just to keep my code up higher in the screen, and

now let's type onActivityResult and hit Enter, and

studio will drop in the method signature for us.

Check out the parameters of this method, the first is the request code,

if we have multiple types of request but always come back to this method.

So we can check this request code of each to handle them in different ways.

We only have one requestCode, but still it's at a check,

if requestCode equals and then we call that REQUEST_FAVORITE.

The second parameter is a resultCode,

we are always going to want to inspect the resultCode as well.

So let's add, If resultCode equals, and then start typing, in all caps,

RESULT_ and the activity class has some predefined result codes,

CANCELED, FIRST_USER, and OK.

You can check the activity API for more info on these.

RESULT_CANCELED is returned when the user hits the back button or we can trigger it

ourselves, we'll use RESULT_OK, so let's select that and add a curly braces.

All right let's follow the flow of control over in DetailActivity.

So I'm going to open that up and now we're starting this activity and

expecting a result.

So we need to create one,

let's do that when the user taps on the favorite checkbox.

So in here, create bottom we're gonna add some lines and

attach an oncheckedchanged listener.

So we type, favoriteCheckbox.setOnCheckedChangeList-

ener and we wanna create a new one just like we do for onclick listeners.

So a new OnCheckedChanged listener,

in here is the method that gets called and in here we need another intent

to hold the data that we want to transfer back to the calling activity.

So let's make one Intent, let's call this result Intent = a new Intent.

Let's add the value of this checkbox as a boolean extra, resultIntent.put[Extra].

And for the name, let's add another static constant in main activity or

call it extra favorite.

We'll define it in a moment but here we can use MainActivity.EXTRA_FAVORITE.

Now this method passes in a boolean is checked that will be

true if the value is checked.

So let's use that.

And now we want to set the result using the activities setResult method.

We'll use like we said RESULT_OK.

But we also want to attach this intent, resultIntent, as a second parameter for

this method.

To finish this activity and

return to the main one, let's call the activities finish method.

Now back in mainActivity let's go up and add that constant we created.

Public static final String and we called it EXTRA_FAVORITE and

let's set it equal to EXTRA_FAVORITE.

Now we need to do something with the result down in our method at the bottom.

So back here where we have our if statements, for

the moment let's just log the result.

So we'll set a boolean variable.

Boolean result equals,

now knows that the intent that's returned is returned as a parameter called data so

we can access it with data.getBooleanExtra and

we have the name EXTRA_FAVORITE.

And let's log it with Log.i.

We have a tag we can use that will say "Is favorite?

" and will append the result Boolean.

And let's check it out.

Whoops, I notice that I have an error here.

So this is happening because the getBooleanExtra method

requires a default value just in case the Boolean isn't present.

So we usually want to set false as our default value.

We also have an error in detail activities, let's go take a look.

And there, now it's resolved, it just need to pick up the change from main activity.

So now let's run this to see how it works.

Okay, so first we need to tap on the download button, and

we come to the detail page, we check the favorite box

And it's gonna go back to main activity and

once it does I saw in logcat that the log entry we added already showed up.

So if I scroll up a little bit, I can see here, is favorite?equals true.

All right round trip communication complete.