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/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.internal.widget;
import android.database.DataSetObservable;
import android.database.DataSetObserver;
import android.os.Parcelable;
import android.view.View;
import android.view.ViewGroup;
/**
* Base class providing the adapter to populate pages inside of
* a {@link android.support.v4.view.ViewPager}. You will most likely want to use a more
* specific implementation of this, such as
* {@link android.support.v4.app.FragmentPagerAdapter} or
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*
* When you implement a PagerAdapter, you must override the following methods
* at minimum:
*
* - {@link #instantiateItem(android.view.ViewGroup, int)}
* - {@link #destroyItem(android.view.ViewGroup, int, Object)}
* - {@link #getCount()}
* - {@link #isViewFromObject(android.view.View, Object)}
*
*
* PagerAdapter is more general than the adapters used for
* {@link android.widget.AdapterView 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
* {@link #startUpdate(android.view.ViewGroup)} indicates that the contents of the ViewPager
* are about to change. One or more calls to {@link #instantiateItem(android.view.ViewGroup, int)}
* and/or {@link #destroyItem(android.view.ViewGroup, int, Object)} will follow, and the end
* of an update will be signaled by a call to {@link #finishUpdate(android.view.ViewGroup)}.
* By the time {@link #finishUpdate(android.view.ViewGroup) finishUpdate} returns the views
* associated with the key objects returned by
* {@link #instantiateItem(android.view.ViewGroup, int) instantiateItem} should be added to
* the parent ViewGroup passed to these methods and the views associated with
* the keys passed to {@link #destroyItem(android.view.ViewGroup, int, Object) destroyItem}
* should be removed. The method {@link #isViewFromObject(android.view.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 {@link #instantiateItem(android.view.ViewGroup, int)}
* after creation and adding them to the parent ViewGroup. A matching
* {@link #destroyItem(android.view.ViewGroup, int, Object)} implementation would remove the
* View from the parent ViewGroup and {@link #isViewFromObject(android.view.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 {@link #notifyDataSetChanged()} similar
* to AdapterView adapters derived from {@link android.widget.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 {@link #getItemPosition(Object)}.
*/
public abstract class PagerAdapter {
private DataSetObservable mObservable = new DataSetObservable();
public static final int POSITION_UNCHANGED = -1;
public static final int POSITION_NONE = -2;
/**
* Return the number of views available.
*/
public abstract int getCount();
/**
* Called when a change in the shown pages is going to start being made.
* @param container The containing View which is displaying this adapter's
* page views.
*/
public void startUpdate(ViewGroup container) {
startUpdate((View) container);
}
/**
* 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
* {@link #finishUpdate(android.view.ViewGroup)}.
*
* @param container The containing View in which the page will be shown.
* @param position The page position to be instantiated.
* @return Returns an Object representing the new page. This does not
* need to be a View, but can be some other container of the page.
*/
public Object instantiateItem(ViewGroup container, int position) {
return instantiateItem((View) container, position);
}
/**
* 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 {@link #finishUpdate(android.view.ViewGroup)}.
*
* @param container The containing View from which the page will be removed.
* @param position The page position to be removed.
* @param object The same object that was returned by
* {@link #instantiateItem(android.view.View, int)}.
*/
public void destroyItem(ViewGroup container, int position, Object object) {
destroyItem((View) container, position, 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.
*
* @param container The containing View from which the page will be removed.
* @param position The page position that is now the primary.
* @param object The same object that was returned by
* {@link #instantiateItem(android.view.View, int)}.
*/
public void setPrimaryItem(ViewGroup container, int position, Object object) {
setPrimaryItem((View) container, position, object);
}
/**
* Called when the 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.
* @param container The containing View which is displaying this adapter's
* page views.
*/
public void finishUpdate(ViewGroup container) {
finishUpdate((View) container);
}
/**
* Called when a change in the shown pages is going to start being made.
* @param container The containing View which is displaying this adapter's
* page views.
*
* @deprecated Use {@link #startUpdate(android.view.ViewGroup)}
*/
public void startUpdate(View container) {
}
/**
* 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
* {@link #finishUpdate(android.view.ViewGroup)}.
*
* @param container The containing View in which the page will be shown.
* @param position The page position to be instantiated.
* @return Returns an Object representing the new page. This does not
* need to be a View, but can be some other container of the page.
*
* @deprecated Use {@link #instantiateItem(android.view.ViewGroup, int)}
*/
public Object instantiateItem(View container, int position) {
throw new UnsupportedOperationException(
"Required method instantiateItem was not overridden");
}
/**
* 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 {@link #finishUpdate(android.view.View)}.
*
* @param container The containing View from which the page will be removed.
* @param position The page position to be removed.
* @param object The same object that was returned by
* {@link #instantiateItem(android.view.View, int)}.
*
* @deprecated Use {@link #destroyItem(android.view.ViewGroup, int, Object)}
*/
public void destroyItem(View container, int position, Object object) {
throw new UnsupportedOperationException("Required method destroyItem was not overridden");
}
/**
* 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.
*
* @param container The containing View from which the page will be removed.
* @param position The page position that is now the primary.
* @param object The same object that was returned by
* {@link #instantiateItem(android.view.View, int)}.
*
* @deprecated Use {@link #setPrimaryItem(android.view.ViewGroup, int, Object)}
*/
public void setPrimaryItem(View container, int position, Object object) {
}
/**
* Called when the 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.
* @param container The containing View which is displaying this adapter's
* page views.
*
* @deprecated Use {@link #finishUpdate(android.view.ViewGroup)}
*/
public void finishUpdate(View container) {
}
/**
* Determines whether a page View is associated with a specific key object
* as returned by {@link #instantiateItem(android.view.ViewGroup, int)}. This method is
* required for a PagerAdapter to function properly.
*
* @param view Page View to check for association with object
* @param object Object to check for association with view
* @return true if view is associated with the key object object
*/
public abstract boolean isViewFromObject(View view, Object object);
/**
* Save any instance state associated with this adapter and its pages that should be
* restored if the current UI state needs to be reconstructed.
*
* @return Saved state for this adapter
*/
public Parcelable saveState() {
return null;
}
/**
* Restore any instance state associated with this adapter and its pages
* that was previously saved by {@link #saveState()}.
*
* @param state State previously saved by a call to {@link #saveState()}
* @param loader A ClassLoader that should be used to instantiate any restored objects
*/
public void restoreState(Parcelable state, ClassLoader loader) {
}
/**
* Called when the host view is attempting to determine if an item's position
* has changed. Returns {@link #POSITION_UNCHANGED} if the position of the given
* item has not changed or {@link #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 {@link #POSITION_UNCHANGED}.
*
* @param object Object representing an item, previously returned by a call to
* {@link #instantiateItem(android.view.View, int)}.
* @return object's new position index from [0, {@link #getCount()}),
* {@link #POSITION_UNCHANGED} if the object's position has not changed,
* or {@link #POSITION_NONE} if the item is no longer present.
*/
public int getItemPosition(Object object) {
return POSITION_UNCHANGED;
}
/**
* This method should be called by the application if the data backing this adapter has changed
* and associated views should update.
*/
public void notifyDataSetChanged() {
mObservable.notifyChanged();
}
/**
* Register an observer to receive callbacks related to the adapter's data changing.
*
* @param observer The {@link android.database.DataSetObserver} which will receive callbacks.
*/
public void registerDataSetObserver(DataSetObserver observer) {
mObservable.registerObserver(observer);
}
/**
* Unregister an observer from callbacks related to the adapter's data changing.
*
* @param observer The {@link android.database.DataSetObserver} which will be unregistered.
*/
public void unregisterDataSetObserver(DataSetObserver observer) {
mObservable.unregisterObserver(observer);
}
/**
* 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.
*
* @param position The position of the title requested
* @return A title for the requested page
*/
public CharSequence getPageTitle(int position) {
return null;
}
/**
* Returns the proportional width of a given page as a percentage of the
* ViewPager's measured width from (0.f-1.f]
*
* @param position The position of the page requested
* @return Proportional width for the given page position
*/
public float getPageWidth(int position) {
return 1.f;
}
}