activities, fragments, and intents · 2016-09-21 · fragments fragments were added to the android...

FRAGMENTS

Fragments

An activity is a container for views

When you have a larger screen device than a phone –like a tablet it can look too simple to use phone interface here.

FragmentsMini-activities, each with its own set of views

One or more fragments can be embedded in an Activity

You can do this dynamically as a function of the device type (tablet or not) or orientation

ALSO, you can reuse fragments --- like reuse of mini interfaces

Fragments

Fragments

Fragments were added to the Android API in

Honeycomb, API 11.

The primary classes related to fragments are:

android.app.Fragment

The base class for all fragment definitions

android.app.FragmentManager

The class for interacting with fragment objects inside an

activity

android.app.FragmentTransaction

The class for performing an atomic set of fragment

operations

FRAGMENTS

A Fragment represents a behavior or a portion of user

interface in an Activity.

You can combine multiple fragments in a single

activity to build a multi-pane UI and reuse a fragment

in multiple activities.

You can think of a fragment as a modular section of

an activity, which has its own lifecycle, receives its

own input events, and which you can add or remove

while the activity is running (sort of like a "sub activity"

that you can reuse in different activities).

A fragment must always be embedded in an activity.

Fragment Lifecycle

Fragment in an Activity---Activity Lifecycle influences

Activity paused all its fragments paused

Activity destroyed all its fragments are

destroyed

Activity running manipulate each fragment

independently.

Fragment transaction add, remove, etc.

adds it to a back stack that's managed by the activity—

each back stack entry in the activity is a record of the

fragment transaction that occurred.

The back stack allows the user to reverse a fragment

transaction (navigate backwards), by pressing the Back

button.

Fragment Lifecycle

Fragment Lifecycle

• Several callback methods to

handle various stages of a

Fragment lifecycle:

• onCreate() called when

creating the Fragment.

• onCreateView() called

when UI for the Fragment is drawn for the first time.

• onPause() called when the

user is leaving the Fragment.

Fragment inside Activity

It lives in a ViewGroup inside the activity's view

hierarchy

Fragment has its own view layout.

Using Fragments

via XML: Insert a fragment into your activity layout by

declaring the fragment in the activity's layout file, as a

<fragment> element,

via CODE: from your application code by adding it to

an existing ViewGroup.

You may also use a fragment without its own UI as

an invisible worker for the activity.

http://developer.android.com/reference/android/view/ViewGroup.html

http://developer.android.com/reference/android/view/ViewGroup.html

Fragment methods

(callback functions)

onAttach(Activity) called once the fragment is associated with its activity.

onCreate(Bundle) called to do initial creation of the fragment.

onCreateView(LayoutInflater, ViewGroup, Bundle)creates and returns the view hierarchy associated with the fragment.

onActivityCreated(Bundle) tells the fragment that its activity has completed its own Activity.onCreaate.

onStart() makes the fragment visible to the user (based on its containing activity being started).

onResume() makes the fragment interacting with the user (based on its containing activity being resumed).

http://developer.android.com/reference/android/app/Fragment.html












http://developer.android.com/reference/android/app/Activity.html





Fragment methods

(callback functions)

As a fragment is no longer being used, it goes through a reverse series of callbacks:

onPause() fragment is no longer interacting with the user either because its activity is being paused or a fragment operation is modifying it in the activity.

onStop() fragment is no longer visible to the user either because its activity is being stopped or a fragment operation is modifying it in the activity.

onDestroyView() allows the fragment to clean up resources associated with its View.

onDestroy() called to do final cleanup of the fragment's state.

onDetach() called immediately prior to the fragment no longer being associated with its activity.











Fragments and their UI

Most fragments will have a UI

You must implement the onCreateView() callback

method, which the Android system calls when it's

time for the fragment to draw its layout.

Your implementation of this method must return a

View that is the root of your fragment's layout.



http://developer.android.com/reference/android/view/View.html

FRAGMENT SUB CLASSES

There are three subclasses of fragments:

DialogFragment : Displays a floating dialog

ListFragment : Displays a list of items that are

managed by an adapter

PreferenceFragment : Displays a hierarchy

of Preference objects as a list

http://developer.android.com/reference/android/preference/Preference.html

Fragment Application

Using Eclipse, create a new Android project and

name it Fragments.

In the res/layout folder, add a new file and name it

fragment1.xml. Populate it with the following:

<?xml version=”1.0” encoding=”utf-8”?>

<LinearLayout

xmlns:android=”http://schemas.android.com/apk/res/android”

android:orientation=”vertical”

android:layout_width=”fill_parent”

android:layout_height=”fill_parent”

android:background=”#00FF00”>


Also in the res/layout folder, add another new file and name it fragment2.xml. Populate it as follows:


<LinearLayout


android:orientation=”vertical”



android:background=”#FFFE00”>


In main.xml, add the following code.


<LinearLayout




android:orientation=”horizontal” >

<fragment

android:name=”com.example.Fragments.Fragment1”

android:id=”@+id/fragment1”

android:layout_weight=”1”

android:layout_width=”0px”

android:layout_height=”match_parent” />


Add two Java class files and name them Fragment1.java and Fragment2.java

public class Fragment1 extends Fragment {

@Override

public View onCreateView(LayoutInflater inflater,

ViewGroup container, Bundle savedInstanceState) {

//---Inflate the layout for this fragment---

return inflater.inflate(

R.layout.fragment1, container, false);

}

}


public class Fragment2 extends Fragment {

@Override

public View onCreateView(LayoutInflater inflater,

ViewGroup container, Bundle savedInstanceState) {

//---Inflate the layout for this fragment---

return inflater.inflate(

R.layout.fragment2, container, false);

}

}


return inflater.inflate( R.layout.fragment1, container, false)

How It Works

A fragment behaves very much like an activity — it has a Java

class and it loads its UI from an XML file.

The Java class for a fragment needs to extend the Fragment

base class.

To draw the UI for a fragment, you override the onCreateView()

method. This method needs to return a View object.

Use a LayoutInflater object to inflate the UI from the specified

XML file.

The container argument refers to the parent ViewGroup, which

is the activity in which you are trying to embed the fragment.

The savedInstanceState argument enables you to restore the

fragment to its previously saved state.

Note that each fragment needs a unique identifier. You can

assign one via the android:id or android:tag attribute.

Adding Fragments

Dynamically

Fragments enable to compartmentalize UI into various

configurable parts.

The real power of fragments is realized when you add them

dynamically to activities during runtime.

It is much more useful to create fragments and add them to

activities during runtime.

This enables you to create a customizable user interface for

your application.

For example, if the application is running on a smartphone, you

might fill an activity with a single fragment; if the application is

running on a tablet, you might then fill the activity with two or

more fragments, as the tablet has much more screen real

estate compared to a smartphone.

Adding Fragments

DynamicallyUsing the same project created in the previous section, modify the main.xml file by

commenting out the two <fragment> elements:

Adding Fragments

DynamicallyAdd the following code in bold to the FragmentsActivity.java file.

public class FragmentsActivity extends Activity {

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

android.app.FragmentManager fragmentManager =

getFragmentManager();

FragmentTransaction fragmentTransaction =

fragmentManager.beginTransaction();

WindowManager wm = getWindowManager();

Display d = wm.getDefaultDisplay();

Adding Fragments

Dynamically

Point size = new Point();

d.getSize(size);

int width = size.x;

int height = size.y;

if (width > height)

{

//---landscape mode---

Fragment1 fragment1 = new Fragment1();

// android.R.id.content refers to the content

// view of the activity

fragmentTransaction.replace(android.R.id.content, fragment1);

}

Adding Fragments

Dynamically

else

{

//---portrait mode---

Fragment2 fragment2 = new Fragment2();

fragmentTransaction.replace(android.R.id.content,

fragment2);

}

fragmentTransaction.commit();

}

}

Adding Fragments

Dynamically

THE END

activities, fragments, and intents · 2016-09-21 · fragments fragments were added to the android...

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