Passing Results Back to Activities

Sometimes we start a second activity with the intention of getting some data to use 0:00 in the original activity. 0:04 We need to specify this when we start the activity by using a different method, 0:05 start activity for result. 0:09 So back here., let's delete this line where we are starting the activity, 0:12 and instead call it startActivityForResult. 0:15 There we go. 0:19 The first parameter like before is our intent, but 0:21 now we also need to include a request code. 0:25 Like with extras, it's a good practice to define some reasonable constants. 0:28 So let's call this REQUEST_FAVORITE and then define it at the top of our class. 0:31 So I'm going to scroll back up to the top in here where we have our static strings. 0:40 Let's do public static final and in this case it's an int or 0:44 request code has to be an int and we called it REQUEST_FAVORITE and 0:48 we can set this to really anything we want let's just set it to zero. 0:52 We'll just count up from different requests values 0:56 are useful when we request different types of information from an activity. 0:59 All right so now we're expecting a result to come back here to main activity. 1:03 How will we handle it? 1:07 Using start activity for result requires that we implement another method 1:09 in the activity to handle the result. 1:13 Let's scroll down all the way to the bottom of our class and have it. 1:15 I'm gonna add a few lines here just to keep my code up higher in the screen, and 1:18 now let's type onActivityResult and hit Enter, and 1:23 studio will drop in the method signature for us. 1:27 Check out the parameters of this method, the first is the request code, 1:30 if we have multiple types of request but always come back to this method. 1:34 So we can check this request code of each to handle them in different ways. 1:37 We only have one requestCode, but still it's at a check, 1:43 if requestCode equals and then we call that REQUEST_FAVORITE. 1:47 The second parameter is a resultCode, 1:53 we are always going to want to inspect the resultCode as well. 1:56 So let's add, If resultCode equals, and then start typing, in all caps, 1:59 RESULT_ and the activity class has some predefined result codes, 2:05 CANCELED, FIRST_USER, and OK. 2:09 You can check the activity API for more info on these. 2:12 RESULT_CANCELED is returned when the user hits the back button or we can trigger it 2:15 ourselves, we'll use RESULT_OK, so let's select that and add a curly braces. 2:18 All right let's follow the flow of control over in DetailActivity. 2:23 So I'm going to open that up and now we're starting this activity and 2:28 expecting a result. 2:32 So we need to create one, 2:34 let's do that when the user taps on the favorite checkbox. 2:35 So in here, create bottom we're gonna add some lines and 2:38 attach an oncheckedchanged listener. 2:42 So we type, favoriteCheckbox.setOnCheckedChangeList- 2:45 ener and we wanna create a new one just like we do for onclick listeners. 2:50 So a new OnCheckedChanged listener, 2:54 in here is the method that gets called and in here we need another intent 2:56 to hold the data that we want to transfer back to the calling activity. 2:59 So let's make one Intent, let's call this result Intent = a new Intent. 3:03 Let's add the value of this checkbox as a boolean extra, resultIntent.put[Extra]. 3:09 And for the name, let's add another static constant in main activity or 3:16 call it extra favorite. 3:20 We'll define it in a moment but here we can use MainActivity.EXTRA_FAVORITE. 3:21 Now this method passes in a boolean is checked that will be 3:30 true if the value is checked. 3:33 So let's use that. 3:34 And now we want to set the result using the activities setResult method. 3:36 We'll use like we said RESULT_OK. 3:41 But we also want to attach this intent, resultIntent, as a second parameter for 3:44 this method. 3:49 To finish this activity and 3:51 return to the main one, let's call the activities finish method. 3:52 Now back in mainActivity let's go up and add that constant we created. 3:57 Public static final String and we called it EXTRA_FAVORITE and 4:01 let's set it equal to EXTRA_FAVORITE. 4:08 Now we need to do something with the result down in our method at the bottom. 4:14 So back here where we have our if statements, for 4:19 the moment let's just log the result. 4:22 So we'll set a boolean variable. 4:24 Boolean result equals, 4:26 now knows that the intent that's returned is returned as a parameter called data so 4:28 we can access it with data.getBooleanExtra and 4:33 we have the name EXTRA_FAVORITE. 4:38 And let's log it with Log.i. 4:42 We have a tag we can use that will say "Is favorite? 4:44 " and will append the result Boolean. 4:48 And let's check it out. 4:52 Whoops, I notice that I have an error here. 4:55 So this is happening because the getBooleanExtra method 4:57 requires a default value just in case the Boolean isn't present. 5:00 So we usually want to set false as our default value. 5:04 We also have an error in detail activities, let's go take a look. 5:07 And there, now it's resolved, it just need to pick up the change from main activity. 5:11 So now let's run this to see how it works. 5:14 Okay, so first we need to tap on the download button, and 5:18 we come to the detail page, we check the favorite box 5:22 And it's gonna go back to main activity and 5:28 once it does I saw in logcat that the log entry we added already showed up. 5:31 So if I scroll up a little bit, I can see here, is favorite?equals true. 5:36 All right round trip communication complete. 5:41