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.Config;
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 = new MyDataSetObserver();
    /**
     * 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;

    /**
     * Constructor. The adapter will call requery() on the cursor whenever
     * it changes so that the most recent data is always displayed.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     */
    public CursorAdapter(Context context, Cursor c) {
        init(context, c, true);
    }

    /**
     * Constructor
     * @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.
     */
    public CursorAdapter(Context context, Cursor c, boolean autoRequery) {
        init(context, c, autoRequery);
    }

    protected void init(Context context, Cursor c, boolean autoRequery) {
        boolean cursorPresent = c != null;
        mAutoRequery = autoRequery;
        mCursor = c;
        mDataValid = cursorPresent;
        mContext = context;
        mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;
        mChangeObserver = new ChangeObserver();
        if (cursorPresent) {
            c.registerContentObserver(mChangeObserver);
            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) {
        if (cursor == mCursor) {
            return;
        }
        if (mCursor != null) {
            mCursor.unregisterContentObserver(mChangeObserver);
            mCursor.unregisterDataSetObserver(mDataSetObserver);
            mCursor.close();
        }
        mCursor = cursor;
        if (cursor != null) {
            cursor.registerContentObserver(mChangeObserver);
            cursor.registerDataSetObserver(mDataSetObserver);
            mRowIDColumn = cursor.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();
        }
    }

    /**
     * <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)
     * @hide pending API Council approval
     */
    protected void onContentChanged() {
        if (mAutoRequery && mCursor != null && !mCursor.isClosed()) {
            if (Config.LOGV) 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();
        }
    }

}