Package icyllis.modernui.widget

Class PagerAdapter

java.lang.Object
icyllis.modernui.widget.PagerAdapter
public abstract class PagerAdapter extends Object
Base class providing the adapter to populate pages inside a ViewPager.

When you implement a PagerAdapter, you must override the following methods at minimum:

PagerAdapter is more general than the adapters used for AdapterViews. Instead of providing a View recycling mechanism directly ViewPager uses callbacks to indicate the steps taken during an update. A PagerAdapter may implement a form of View recycling if desired or use a more sophisticated method of managing page Views such as Fragment transactions where each page is represented by its own Fragment.

ViewPager associates each page with a key Object instead of working with Views directly. This key is used to track and uniquely identify a given page independent of its position in the adapter. A call to the PagerAdapter method startUpdate(ViewGroup) indicates that the contents of the ViewPager are about to change. One or more calls to instantiateItem(ViewGroup, int) and/or destroyItem(ViewGroup, int, Object) will follow, and the end of an update will be signaled by a call to finishUpdate(ViewGroup). By the time finishUpdate returns the views associated with the key objects returned by instantiateItem should be added to the parent ViewGroup passed to these methods and the views associated with the keys passed to destroyItem should be removed. The method isViewFromObject(View, Object) identifies whether a page View is associated with a given key object.

A very simple PagerAdapter may choose to use the page Views themselves as key objects, returning them from instantiateItem(ViewGroup, int) after creation and adding them to the parent ViewGroup. A matching destroyItem(ViewGroup, int, Object) implementation would remove the View from the parent ViewGroup and isViewFromObject(View, Object) could be implemented as return view == object;.

PagerAdapter supports data set changes. Data set changes must occur on the main thread and must end with a call to notifyDataSetChanged() similar to AdapterView adapters derived from BaseAdapter. A data set change may involve pages being added, removed, or changing position. The ViewPager will keep the current page active provided the adapter implements the method getItemPosition(Object).

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    POSITION_NONE
     
    static final int
    POSITION_UNCHANGED
     

  • Constructor Summary

    Constructors
    Constructor
    Description
    PagerAdapter()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    abstract void
    destroyItem(ViewGroup container, int position, Object object)
    Remove a page for the given position.
    The adapter is responsible for removing the view from its container, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).
    void
    finishUpdate(ViewGroup container)
    Called when a change in the shown pages has been completed.
    At this point you must ensure that all of the pages have actually been added or removed from the container as appropriate.
    abstract int
    getCount()
    Return the number of views available.
    int
    getItemPosition(Object object)
    Called when the host view is attempting to determine if an item's position has changed.
    CharSequence
    getPageTitle(int position)
    This method may be called by the ViewPager to obtain a title string to describe the specified page.
    float
    getPageWidth(int position)
    Returns the proportional width of a given page as a percentage of the ViewPager's measured width from (0.f-1.f]
    abstract Object
    instantiateItem(ViewGroup container, int position)
    Create the page for the given position.
    The adapter is responsible for adding the view to the container given here, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).
    abstract boolean
    isViewFromObject(View view, Object object)
    Determines whether a page View is associated with a specific key object as returned by instantiateItem(ViewGroup, int).
    void
    notifyDataSetChanged()
    This method should be called by the application if the data backing this adapter has changed and associated views should update.
    void
    registerDataSetObserver(DataSetObserver observer)
    Register an observer to receive callbacks related to the adapter's data changing.
    void
    restoreState(Parcelable state, ClassLoader loader)
    Restore any instance state associated with this adapter and its pages that was previously saved by saveState().
    Parcelable
    saveState()
    Save any instance state associated with this adapter and its pages that should be restored if the current UI state needs to be reconstructed.
    void
    setPrimaryItem(ViewGroup container, int position, Object object)
    Called to inform the adapter of which item is currently considered to be the "primary", that is the one show to the user as the current page.
    void
    startUpdate(ViewGroup container)
    Called when a change in the shown pages is going to start being made.
    void
    unregisterDataSetObserver(DataSetObserver observer)
    Unregister an observer from callbacks related to the adapter's data changing.

    Methods inherited from class java.lang.Object

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

  • Field Details

  • Constructor Details

    • PagerAdapter

      public PagerAdapter()

  • Method Details

    • getCount

      public abstract int getCount()
      Return the number of views available.

    • startUpdate

      public void startUpdate(@NonNull ViewGroup container)
      Called when a change in the shown pages is going to start being made.
      Parameters:
      container - The containing View which is displaying this adapter's page views.

    • instantiateItem

      @NonNull public abstract Object instantiateItem(@NonNull ViewGroup container, int position)
      Create the page for the given position.
      The adapter is responsible for adding the view to the container given here, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).
      Parameters:
      container - The containing View in which the page will be shown.
      position - The page position to be instantiated.
      Returns:
      Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

    • destroyItem

      public abstract void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object)
      Remove a page for the given position.
      The adapter is responsible for removing the view from its container, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).
      Parameters:
      container - The containing View from which the page will be removed.
      position - The page position to be removed.
      object - The same object that was returned by instantiateItem(ViewGroup, int).

    • setPrimaryItem

      public void setPrimaryItem(@NonNull ViewGroup container, int position, @NonNull Object object)
      Called to inform the adapter of which item is currently considered to be the "primary", that is the one show to the user as the current page. This method will not be invoked when the adapter contains no items.
      Parameters:
      container - The containing View from which the page will be removed.
      position - The page position that is now the primary.
      object - The same object that was returned by instantiateItem(ViewGroup, int).

    • finishUpdate

      public void finishUpdate(@NonNull ViewGroup container)
      Called when a change in the shown pages has been completed.
      At this point you must ensure that all of the pages have actually been added or removed from the container as appropriate.
      Parameters:
      container - The containing View which is displaying this adapter's page views.

    • isViewFromObject

      public abstract boolean isViewFromObject(@NonNull View view, @NonNull Object object)
      Determines whether a page View is associated with a specific key object as returned by instantiateItem(ViewGroup, int). This method is required for a PagerAdapter to function properly.
      Parameters:
      view - Page View to check for association with object
      object - Object to check for association with view
      Returns:
      true if view is associated with the key object object

    • saveState

      @Nullable public Parcelable saveState()
      Save any instance state associated with this adapter and its pages that should be restored if the current UI state needs to be reconstructed.
      Returns:
      Saved state for this adapter

    • restoreState

      public void restoreState(@Nullable Parcelable state, @Nullable ClassLoader loader)
      Restore any instance state associated with this adapter and its pages that was previously saved by saveState().
      Parameters:
      state - State previously saved by a call to saveState()
      loader - A ClassLoader that should be used to instantiate any restored objects

    • getItemPosition

      public int getItemPosition(@NonNull Object object)
      Called when the host view is attempting to determine if an item's position has changed. Returns POSITION_UNCHANGED if the position of the given item has not changed or POSITION_NONE if the item is no longer present in the adapter.

      The default implementation assumes that items will never change position and always returns POSITION_UNCHANGED.

      Parameters:
      object - Object representing an item, previously returned by a call to instantiateItem(ViewGroup, int).
      Returns:
      object's new position index from [0, getCount()), POSITION_UNCHANGED if the object's position has not changed, or POSITION_NONE if the item is no longer present.

    • notifyDataSetChanged

      public void notifyDataSetChanged()
      This method should be called by the application if the data backing this adapter has changed and associated views should update.

    • registerDataSetObserver

      public void registerDataSetObserver(@NonNull DataSetObserver observer)
      Register an observer to receive callbacks related to the adapter's data changing.
      Parameters:
      observer - The DataSetObserver which will receive callbacks.

    • unregisterDataSetObserver

      public void unregisterDataSetObserver(@NonNull DataSetObserver observer)
      Unregister an observer from callbacks related to the adapter's data changing.
      Parameters:
      observer - The DataSetObserver which will be unregistered.

    • getPageTitle

      @Nullable public CharSequence getPageTitle(int position)
      This method may be called by the ViewPager to obtain a title string to describe the specified page. This method may return null indicating no title for this page. The default implementation returns null.
      Parameters:
      position - The position of the title requested
      Returns:
      A title for the requested page

    • getPageWidth

      public float getPageWidth(int position)
      Returns the proportional width of a given page as a percentage of the ViewPager's measured width from (0.f-1.f]
      Parameters:
      position - The position of the page requested
      Returns:
      Proportional width for the given page position