On a smartphone you jump to a new detail screen. This is depicted in the following graphic. The following discussion will assume that you have two fragments main and detail , but you can also have more. We will also have one main activity and one detailed activity. On a tablet the main activity contains both fragments in its layout, on a handheld it only contains the main fragment. Therefore you have to use the getActivity method to get the parent activity. It is possible to define in the layout file of an activity that it contains fragments static definition.
You can also modify the fragments of an activity at runtime dynamic definition. Use one activity, which displays two fragments for tablets and on handset devices. In this case change at runtime the fragments displayed by the activity whenever necessary. In this scenario you typically define instances of the FrameLayout class as placeholder in your layout and add the fragments at runtime to them. Use separate activities to host each fragment on a handset.
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An activity may include multiple fragments for a certain configuration and for other configurations a different number. If a detailed fragment is there, the main activity tells the fragment that it should update itself. If a detail fragment is not available, the main activity starts the detailed activity. Which option to select depends on the use case, typical the dynamic contribution is more flexible bit a bit harder to implement.
To define a new fragment you either extend the android.
Fragment class or one of its subclasses. The following code shows an example implementation. To increase reuse of fragments, they should not directly communicate with each other. Every communication of the fragments should be done via the host activity. For this purpose a fragment should define an interface as an inner type.
The fragment requires that the activity, which uses it, must implement this interface. This way you avoid that the fragment has any knowledge about the activity which uses it. In its onAttach method it can check if the activity correctly implements this interface. For example, assume you have a fragment which should communicate a value to its parent activity.
This can be implemented like the following.
Fragments and Run-ons
A fragment has its own life cycle. But it is always connected to the life cycle of the activity which uses the fragment. If an activity stops, its fragments are also stopped. If an activity is destroyed, its fragments are also destroyed. The fragment instance is associated with an activity instance. The fragment and the activity is not fully initialized. Typically you get in this method a reference to the activity which uses the fragment for further initialization work.
Fragment is created.
The onCreate method is called after the onCreate method of the activity but before the onCreateView method of the fragment. The fragment instance creates its view hierarchy.
In the onCreateView method the fragment creates its user interface. Here you can inflate a layout via the inflate method call of the Inflator object passed as a parameter to this method. In this method you should not interactive with the activity, the activity is not yet fully initialized. There is no need to implement this method for headless fragments. The inflated views become part of the view hierarchy of its containing activity.
The onActivityCreated is called after the onCreateView method when the host activity is created. Activity and fragment instance have been created as well as the view hierarchy of the activity.
At this point, view can be accessed with the findViewById method. In this method you can instantiate objects which require a Context object. Fragment is visible but becomes not active anymore, e. Destroys the view of the fragment. If the fragment is recreated from the backstack this method is called and afterwards the onCreateView method.
To use your new fragment, you can statically add it to an XML layout. In this case the android:name attribute points to the corresponding class as demonstrated by the following code snippet. Using this scenario makes sense in case you have different static layout files for different device configurations. The FragmentManager class allows you to add, remove and replace fragments in the layout of your activity.
It can accessed in an activity via the getFragmentManager method. The modifications must be performed in a transaction via the FragmentTransaction class. To modify the fragments in an activity you typically define a FrameLayout placeholder in the layout file. If you want to add the transaction to the backstack of Android, you use the addToBackStack method. This adds the action to the history stack of the activity and allows the user to revert this change via the back button.
Stylistic Sentence Fragments
To check if a fragment is part of your layout you can use the FragmentManager class. The isInLayout method works on if the fragment as added to the activity via its layout. There are several approaches to perform this. One way is to define a configuration file in the values resource folder. In the values-land folder you would place a config. You can add a FragmentTransition to the backstack to allow the user to use the back button to reverse the transition.
You can also use several standard Android animations via the setTransition method call. These are defined via the constants starting with FragmentTransaction. Frequently in your Android application you need to persist your application data. For this, you can for example use an SQLite database or a file. If you want to persist data between configuration changes, you can also use the application object. In addition to that you can use the setRetainState true method call on the fragment. This retains the fragment instances between configuration changes.
It only works if the fragments are not added to the backstack. In this case the data must be stored as member field. You can use the onSaveInstanceState method to place the data in the Bundle. You can retrieve that data the onActivityCreated method. Fragments can be used without defining a user interface. These are called headless fragments. To implement such a fragment, return null in the onCreateView method of your fragment. It is recommended to use services for background processing. If you want to do this via your fragments, the second best solution is to use headless fragments in combination with the setRetainInstance method.
Headless fragment are typically used to encapsulate some state across configuration changes or for a background processing task.
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For this purpose you would set your headless fragment to be retained. A retained fragment is not destroyed during configuration changes. To add such a fragment to an activity you use the add method of the FragmentManager class. If you need to refer to this Fragment later, you need to add it with a tag. The usage of the onRetainNonConfigurationInstance in the activity is deprecated and should be replaced by retained headless fragments. A DialogFragment is a special fragment that displays a modal window, floating on top of the current activity window.
An instance of DialogFragment can be used to display an existing Dialog implementation dialog or a custom view hierarchy. The Dialog class is the base class for implementing a dialog. Your DialogFragment can implement the onCreateDialog method and return such a dialog implementation. If you want to create your custom view hierarchy you can build this in the onCreateView method of the fragment.
Your implementation of DialogFragment communicates similar to other fragments to the activity. One possible approach is that the fragment defines an interface which the activity must implement. The fragment can call back into the activity without knowing the implementation details of the activity.
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An alternative approach is to use a shared ViewModel in which the fragment changes state which can trigger a method in the activity. The following tutorial demonstrates how to use fragments in a standard Android application. It does not use the support library. The application uses different numbers of fragments depending on portrait and landscape mode.
In portrait mode the main activity shows one fragment. From this fragment the user can navigate to another activity which contains another fragment. Currently the wizard does select it by default, in this case you need to change it. Ensure that this option is not selected. Verify that you activity extends Activity to ensure you are not using the backwards compatibility mode.
If you extends another class, delete the project and create it again. Ensure that you deselect the "Backward Compatibility" flag in the project creation wizard. Create the following classes which are used as fragments. Start with the DetailFragment class. Create the MyListFragment class. Despite its name it will not display a list of items. Instead it will just have a button which allow to send the current time to the details fragment. Change the RssfeedActivity class so that it can act as call back for the list fragment and update the detailed fragment.
Start your application. Both fragments should be displayed both in landscape and portrait mode. You can use the emulator controls to change the orientation of the emulator. If you press the button in the ListFragment , the DetailFragment gets updated. The RssfeedActivity should show two fragments two panes if started in landscape mode.
If it is started in portrait mode only one fragment should be shown. In this exercise you adjust your application to support this. It leaves us wondering what happened because of the rain. To complete it, we need further explanation:. Because of the rain, the party was canceled. Now the fragment has become a dependent clause attached to a sentence that has a subject the party and a verb was canceled.
Our thought is complete. In that example, making the sentence longer was the solution. This teensy sentence is complete: I ran. I ran may be a short thought, but it has a subject I and a verb ran. Nothing in the sentence demands further explanation. Avoiding sentence fragments not only makes your writing easier to read, but it can also make you sound more polished in polite correspondence.
That sentence lacks a subject. Fragments can sound as if they are carelessly blurted out. Fixing a sentence fragment involves one of two things: giving it the components it lacks or fastening it onto an independent clause. Consider the following: There are many ways to frighten little brothers.
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For example, by hiding under their beds and waiting for dark. While this writer has great ideas when it comes to stealth, that second statement is not a complete sentence. It lacks a subject. There are two ways to fix this sentence. The first would be to latch it onto the complete sentence before it. Semicolons are great for connecting dependent clauses beginning with for example and however: There are many ways to frighten little brothers; for example, by hiding under their beds and waiting for dark. If that seems too formal for your purposes, you could fortify the fragment with a subject you and verbs for the subject to act on.
There are many ways to frighten little brothers. For example, you could hide under their beds and wait for dark. Without question, you should avoid sentence fragments in formal situations and academic writing.