universum.studios.android.pager.adapter

Class FragmentStatePagerAdapter

java.lang.Object

androidx.viewpager.widget.PagerAdapter

universum.studios.android.pager.adapter.FragmentStatePagerAdapter

public abstract class FragmentStatePagerAdapter
extends androidx.viewpager.widget.PagerAdapter

A PagerAdapter implementation that represents each page as a Fragment. This pager adapter also handles saving and restoring state of its fragments.

This version of the pager adapter is more useful when there are a large number of pages, working more like a list view. When pages are not visible to a user, their entire fragment may be destroyed, only keeping the saved state of that fragment. This allows to the pager to hold on to much less memory associated with each visited page as compared to FragmentPagerAdapter at the cost of potentially more overhead when switching between pages.

Note, that when using FragmentStatePagerAdapter, the host ViewPager must have a valid ID set, otherwise this adapter implementation will throw an exception.

The inheritance hierarchies only need to implement getItem(int) and PagerAdapter.getCount() to become a fully working adapters.

Not persistent data set

If this adapter is used with not-persistent data set like Cursor it is essential to override also getItemId(int) and provide item id for the requested position as this adapter tracks and stores its created fragments by theirs associated item ids. Item ids are also used to store states of the adapter's fragments. Also note, that PagerAdapter.getItemPosition(Object) method should be implemented in a way which can properly resolve whether a fragment should be still visible at its current position, moved to a different position or to be completely removed due to changes in the data set.

Since:

1.0

Author:

Martin Albedinsky

Field Summary

Fields

Modifier and Type	Field and Description
static long	NO_ID Constant used to identify unspecified id.
static int	NO_POSITION Constant used to identify unspecified position.

Fields inherited from class androidx.viewpager.widget.PagerAdapter

POSITION_NONE, POSITION_UNCHANGED

Constructor Summary

Constructors

Constructor and Description
FragmentStatePagerAdapter(androidx.fragment.app.FragmentManager fragmentManager) Creates a new instance of FragmentStatePagerAdapter with the specified fragmentManager.

Method Summary

Modifier and Type	Method and Description
void	destroyItem(android.view.ViewGroup container, int position, Object object)
void	finishUpdate(android.view.ViewGroup container)
abstract androidx.fragment.app.Fragment	getItem(int position) Instantiates a new Fragment associated with the specified position.
long	getItemId(int position) Returns a unique identifier for the item at the specified position.
androidx.fragment.app.Fragment	getPrimaryFragment() Returns the fragment instance that has been set as primary item via setPrimaryItem(ViewGroup, int, Object).
int	getPrimaryPosition() Returns position of the current primary item.
Object	instantiateItem(android.view.ViewGroup container, int position)
boolean	isViewFromObject(android.view.View view, Object object)
protected String	makeItemTag(int containerId, long itemId) Makes a tag for an item with the given itemId.
void	restoreState(android.os.Parcelable state, ClassLoader loader)
android.os.Parcelable	saveState()
protected void	setMakeItemTags(boolean makeItemTags) Sets a boolean flag indicating whether this pager adapter should make tags for its items or not.
void	setPrimaryItem(android.view.ViewGroup container, int position, Object object)
void	startUpdate(android.view.ViewGroup container)

Methods inherited from class androidx.viewpager.widget.PagerAdapter

destroyItem, finishUpdate, getCount, getItemPosition, getPageTitle, getPageWidth, instantiateItem, notifyDataSetChanged, registerDataSetObserver, setPrimaryItem, startUpdate, unregisterDataSetObserver

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

NO_POSITION

public static final int NO_POSITION

Constant used to identify unspecified position.

See Also:

Constant Field Values

NO_ID

public static final long NO_ID

Constant used to identify unspecified id.

See Also:

Constant Field Values

Constructor Detail

FragmentStatePagerAdapter

public FragmentStatePagerAdapter(@NonNull
                                 androidx.fragment.app.FragmentManager fragmentManager)

Creates a new instance of FragmentStatePagerAdapter with the specified fragmentManager.

Parameters:

fragmentManager - The manager used to manage fragments provided by the pager adapter.

Method Detail

startUpdate

public void startUpdate(@NonNull
                        android.view.ViewGroup container)

Overrides:

startUpdate in class androidx.viewpager.widget.PagerAdapter

instantiateItem

@NonNull
public Object instantiateItem(@NonNull
                                       android.view.ViewGroup container,
                                       int position)

Overrides:

instantiateItem in class androidx.viewpager.widget.PagerAdapter

setMakeItemTags

protected final void setMakeItemTags(boolean makeItemTags)

Sets a boolean flag indicating whether this pager adapter should make tags for its items or not.

This feature is by default enabled.

Parameters:

makeItemTags - True to enable making of item tags, false otherwise.

See Also:

makeItemTag(int, long)

makeItemTag

@Nullable
protected String makeItemTag(@IdRes
                                       int containerId,
                                       long itemId)

Makes a tag for an item with the given itemId.

By default making of item tags is disabled and the default implementation makes tag in the following format:

 "android:pager:CONTAINER_ID:ITEM_ID"
 

This feature may be enabled/disabled via setMakeItemTags(boolean).

Parameters:

containerId - Id of the associated view pager container.

itemId - Id of the item for which to create its corresponding tag.

Returns:

Item's tag or null if this adapter does not create tags for its items.

getItemId

public long getItemId(int position)

Returns a unique identifier for the item at the specified position.

The default implementation returns the given position. The inheritance hierarchies should override this method if they have better way to uniquely identify their items.

Note that this method may be called also from destroyItem(ViewGroup, int, Object) when, possibly, the data set of this adapter may be already invalid. In such case it is safe to return NO_ID.

Parameters:

position - Position from the range of size of items of this adapter.

Returns:

Unique identifier for the item at the requested position.

getItem

@NonNull
public abstract androidx.fragment.app.Fragment getItem(int position)

Instantiates a new Fragment associated with the specified position.

See Also:

instantiateItem(ViewGroup, int)

setPrimaryItem

public void setPrimaryItem(@NonNull
                           android.view.ViewGroup container,
                           int position,
                           @Nullable
                           Object object)

Overrides:

setPrimaryItem in class androidx.viewpager.widget.PagerAdapter

getPrimaryFragment

@Nullable
public androidx.fragment.app.Fragment getPrimaryFragment()

Returns the fragment instance that has been set as primary item via setPrimaryItem(ViewGroup, int, Object).

Returns:

Currently primary fragment. May be null if no primary item has been set yet.

See Also:

getPrimaryPosition()

getPrimaryPosition

public int getPrimaryPosition()

Returns position of the current primary item.

Returns:

Primary item's position or NO_POSITION if no primary item has been specified yet.

See Also:

getPrimaryFragment(), setPrimaryItem(ViewGroup, int, Object)

isViewFromObject

public boolean isViewFromObject(@NonNull
                                android.view.View view,
                                @NonNull
                                Object object)

Specified by:

isViewFromObject in class androidx.viewpager.widget.PagerAdapter

destroyItem

public void destroyItem(@NonNull
                        android.view.ViewGroup container,
                        int position,
                        @NonNull
                        Object object)

Overrides:

destroyItem in class androidx.viewpager.widget.PagerAdapter

finishUpdate

public void finishUpdate(@NonNull
                         android.view.ViewGroup container)

Overrides:

finishUpdate in class androidx.viewpager.widget.PagerAdapter

saveState

public android.os.Parcelable saveState()

Overrides:

saveState in class androidx.viewpager.widget.PagerAdapter

restoreState

public void restoreState(@Nullable
                         android.os.Parcelable state,
                         @Nullable
                         ClassLoader loader)

Overrides:

restoreState in class androidx.viewpager.widget.PagerAdapter