core/java/android/widget/CursorAdapter.java

/*
 * Copyright (C) 2006 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 android.widget;

import android.content.Context;
import android.database.ContentObserver;
import android.database.Cursor;
import android.database.DataSetObserver;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;

/**
 * Adapter that exposes data from a {@link android.database.Cursor Cursor} to a 
 * {@link android.widget.ListView ListView} widget. The Cursor must include 
 * a column named "_id" or this class will not work.
 */
public abstract class CursorAdapter extends BaseAdapter implements Filterable,
        CursorFilter.CursorFilterClient {
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected boolean mDataValid;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected boolean mAutoRequery;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected Cursor mCursor;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected Context mContext;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected int mRowIDColumn;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected ChangeObserver mChangeObserver;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected DataSetObserver mDataSetObserver;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected CursorFilter mCursorFilter;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected FilterQueryProvider mFilterQueryProvider;

    /**
     * If set the adapter will call requery() on the cursor whenever a content change
     * notification is delivered. Implies {@link #FLAG_REGISTER_CONTENT_OBSERVER}.
     *
     * @deprecated This option is discouraged, as it results in Cursor queries
     * being performed on the application's UI thread and thus can cause poor
     * responsiveness or even Application Not Responding errors.  As an alternative,
     * use {@link android.app.LoaderManager} with a {@link android.content.CursorLoader}.
     */
    @Deprecated
    public static final int FLAG_AUTO_REQUERY = 0x01;

    /**
     * If set the adapter will register a content observer on the cursor and will call
     * {@link #onContentChanged()} when a notification comes in.  Be careful when
     * using this flag: you will need to unset the current Cursor from the adapter
     * to avoid leaks due to its registered observers.  This flag is not needed
     * when using a CursorAdapter with a
     * {@link android.content.CursorLoader}.
     */
    public static final int FLAG_REGISTER_CONTENT_OBSERVER = 0x02;

    /**
     * Constructor that always enables auto-requery.
     *
     * @deprecated This option is discouraged, as it results in Cursor queries
     * being performed on the application's UI thread and thus can cause poor
     * responsiveness or even Application Not Responding errors.  As an alternative,
     * use {@link android.app.LoaderManager} with a {@link android.content.CursorLoader}.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     */
    @Deprecated
    public CursorAdapter(Context context, Cursor c) {
        init(context, c, FLAG_AUTO_REQUERY);
    }

    /**
     * Constructor that allows control over auto-requery.  It is recommended
     * you not use this, but instead {@link #CursorAdapter(Context, Cursor, int)}.
     * When using this constructor, {@link #FLAG_REGISTER_CONTENT_OBSERVER}
     * will always be set.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     * @param autoRequery If true the adapter will call requery() on the
     *                    cursor whenever it changes so the most recent
     *                    data is always displayed.  Using true here is discouraged.
     */
    public CursorAdapter(Context context, Cursor c, boolean autoRequery) {
        init(context, c, autoRequery ? FLAG_AUTO_REQUERY : FLAG_REGISTER_CONTENT_OBSERVER);
    }

    /**
     * Recommended constructor.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     * @param flags Flags used to determine the behavior of the adapter; may
     * be any combination of {@link #FLAG_AUTO_REQUERY} and
     * {@link #FLAG_REGISTER_CONTENT_OBSERVER}.
     */
    public CursorAdapter(Context context, Cursor c, int flags) {
        init(context, c, flags);
    }

    /**
     * @deprecated Don't use this, use the normal constructor.  This will
     * be removed in the future.
     */
    @Deprecated
    protected void init(Context context, Cursor c, boolean autoRequery) {
        init(context, c, autoRequery ? FLAG_AUTO_REQUERY : FLAG_REGISTER_CONTENT_OBSERVER);
    }

    void init(Context context, Cursor c, int flags) {
        if ((flags & FLAG_AUTO_REQUERY) == FLAG_AUTO_REQUERY) {
            flags |= FLAG_REGISTER_CONTENT_OBSERVER;
            mAutoRequery = true;
        } else {
            mAutoRequery = false;
        }
        boolean cursorPresent = c != null;
        mCursor = c;
        mDataValid = cursorPresent;
        mContext = context;
        mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;
        if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) {
            mChangeObserver = new ChangeObserver();
            mDataSetObserver = new MyDataSetObserver();
        } else {
            mChangeObserver = null;
            mDataSetObserver = null;
        }

        if (cursorPresent) {
            if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);
        }
    }

    /**
     * Returns the cursor.
     * @return the cursor.
     */
    public Cursor getCursor() {
        return mCursor;
    }

    /**
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        if (mDataValid && mCursor != null) {
            return mCursor.getCount();
        } else {
            return 0;
        }
    }
    
    /**
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        if (mDataValid && mCursor != null) {
            mCursor.moveToPosition(position);
            return mCursor;
        } else {
            return null;
        }
    }

    /**
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        if (mDataValid && mCursor != null) {
            if (mCursor.moveToPosition(position)) {
                return mCursor.getLong(mRowIDColumn);
            } else {
                return 0;
            }
        } else {
            return 0;
        }
    }
    
    @Override
    public boolean hasStableIds() {
        return true;
    }

    /**
     * @see android.widget.ListAdapter#getView(int, View, ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(position)) {
            throw new IllegalStateException("couldn't move cursor to position " + position);
        }
        View v;
        if (convertView == null) {
            v = newView(mContext, mCursor, parent);
        } else {
            v = convertView;
        }
        bindView(v, mContext, mCursor);
        return v;
    }

    @Override
    public View getDropDownView(int position, View convertView, ViewGroup parent) {
        if (mDataValid) {
            mCursor.moveToPosition(position);
            View v;
            if (convertView == null) {
                v = newDropDownView(mContext, mCursor, parent);
            } else {
                v = convertView;
            }
            bindView(v, mContext, mCursor);
            return v;
        } else {
            return null;
        }
    }
    
    /**
     * Makes a new view to hold the data pointed to by cursor.
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     * @param parent The parent to which the new view is attached to
     * @return the newly created view.
     */
    public abstract View newView(Context context, Cursor cursor, ViewGroup parent);

    /**
     * Makes a new drop down view to hold the data pointed to by cursor.
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     * @param parent The parent to which the new view is attached to
     * @return the newly created view.
     */
    public View newDropDownView(Context context, Cursor cursor, ViewGroup parent) {
        return newView(context, cursor, parent);
    }

    /**
     * Bind an existing view to the data pointed to by cursor
     * @param view Existing view, returned earlier by newView
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     */
    public abstract void bindView(View view, Context context, Cursor cursor);
    
    /**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     * 
     * @param cursor The new cursor to be used
     */
    public void changeCursor(Cursor cursor) {
        Cursor old = swapCursor(cursor);
        if (old != null) {
            old.close();
        }
    }

    /**
     * Swap in a new Cursor, returning the old Cursor.  Unlike
     * {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>
     * closed.
     *
     * @param newCursor The new cursor to be used.
     * @return Returns the previously set Cursor, or null if there wasa not one.
     * If the given new Cursor is the same instance is the previously set
     * Cursor, null is also returned.
     */
    public Cursor swapCursor(Cursor newCursor) {
        if (newCursor == mCursor) {
            return null;
        }
        Cursor oldCursor = mCursor;
        if (oldCursor != null) {
            if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver);
            if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver);
        }
        mCursor = newCursor;
        if (newCursor != null) {
            if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver);
            mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
            mDataValid = true;
            // notify the observers about the new cursor
            notifyDataSetChanged();
        } else {
            mRowIDColumn = -1;
            mDataValid = false;
            // notify the observers about the lack of a data set
            notifyDataSetInvalidated();
        }
        return oldCursor;
    }

    /**
     * <p>Converts the cursor into a CharSequence. Subclasses should override this
     * method to convert their results. The default implementation returns an
     * empty String for null values or the default String representation of
     * the value.</p>
     *
     * @param cursor the cursor to convert to a CharSequence
     * @return a CharSequence representing the value
     */
    public CharSequence convertToString(Cursor cursor) {
        return cursor == null ? "" : cursor.toString();
    }

    /**
     * Runs a query with the specified constraint. This query is requested
     * by the filter attached to this adapter.
     *
     * The query is provided by a
     * {@link android.widget.FilterQueryProvider}.
     * If no provider is specified, the current cursor is not filtered and returned.
     *
     * After this method returns the resulting cursor is passed to {@link #changeCursor(Cursor)}
     * and the previous cursor is closed.
     *
     * This method is always executed on a background thread, not on the
     * application's main thread (or UI thread.)
     * 
     * Contract: when constraint is null or empty, the original results,
     * prior to any filtering, must be returned.
     *
     * @param constraint the constraint with which the query must be filtered
     *
     * @return a Cursor representing the results of the new query
     *
     * @see #getFilter()
     * @see #getFilterQueryProvider()
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     */
    public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
        if (mFilterQueryProvider != null) {
            return mFilterQueryProvider.runQuery(constraint);
        }

        return mCursor;
    }

    public Filter getFilter() {
        if (mCursorFilter == null) {
            mCursorFilter = new CursorFilter(this);
        }
        return mCursorFilter;
    }

    /**
     * Returns the query filter provider used for filtering. When the
     * provider is null, no filtering occurs.
     *
     * @return the current filter query provider or null if it does not exist
     *
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public FilterQueryProvider getFilterQueryProvider() {
        return mFilterQueryProvider;
    }

    /**
     * Sets the query filter provider used to filter the current Cursor.
     * The provider's
     * {@link android.widget.FilterQueryProvider#runQuery(CharSequence)}
     * method is invoked when filtering is requested by a client of
     * this adapter.
     *
     * @param filterQueryProvider the filter query provider or null to remove it
     *
     * @see #getFilterQueryProvider()
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public void setFilterQueryProvider(FilterQueryProvider filterQueryProvider) {
        mFilterQueryProvider = filterQueryProvider;
    }

    /**
     * Called when the {@link ContentObserver} on the cursor receives a change notification.
     * The default implementation provides the auto-requery logic, but may be overridden by
     * sub classes.
     * 
     * @see ContentObserver#onChange(boolean)
     */
    protected void onContentChanged() {
        if (mAutoRequery && mCursor != null && !mCursor.isClosed()) {
            if (false) Log.v("Cursor", "Auto requerying " + mCursor + " due to update");
            mDataValid = mCursor.requery();
        }
    }

    private class ChangeObserver extends ContentObserver {
        public ChangeObserver() {
            super(new Handler());
        }

        @Override
        public boolean deliverSelfNotifications() {
            return true;
        }

        @Override
        public void onChange(boolean selfChange) {
            onContentChanged();
        }
    }

    private class MyDataSetObserver extends DataSetObserver {
        @Override
        public void onChanged() {
            mDataValid = true;
            notifyDataSetChanged();
        }

        @Override
        public void onInvalidated() {
            mDataValid = false;
            notifyDataSetInvalidated();
        }
    }

}