core/java/android/widget/SimpleCursorAdapter.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.Cursor;
import android.net.Uri;
import android.view.View;
import android.view.ViewGroup;

/**
 * An easy adapter to map columns from a cursor to TextViews or ImageViews
 * defined in an XML file. You can specify which columns you want, which
 * views you want to display the columns, and the XML file that defines
 * the appearance of these views.
 *
 * Binding occurs in two phases. First, if a
 * {@link android.widget.SimpleCursorAdapter.ViewBinder} is available,
 * {@link ViewBinder#setViewValue(android.view.View, android.database.Cursor, int)}
 * is invoked. If the returned value is true, binding has occured. If the
 * returned value is false and the view to bind is a TextView,
 * {@link #setViewText(TextView, String)} is invoked. If the returned value
 * is false and the view to bind is an ImageView,
 * {@link #setViewImage(ImageView, String)} is invoked. If no appropriate
 * binding can be found, an {@link IllegalStateException} is thrown.
 *
 * If this adapter is used with filtering, for instance in an
 * {@link android.widget.AutoCompleteTextView}, you can use the
 * {@link android.widget.SimpleCursorAdapter.CursorToStringConverter} and the
 * {@link android.widget.FilterQueryProvider} interfaces
 * to get control over the filtering process. You can refer to
 * {@link #convertToString(android.database.Cursor)} and
 * {@link #runQueryOnBackgroundThread(CharSequence)} for more information.
 */
public class SimpleCursorAdapter extends ResourceCursorAdapter {
    /**
     * A list of columns containing the data to bind to the UI.
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected int[] mFrom;
    /**
     * A list of View ids representing the views to which the data must be bound.
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected int[] mTo;

    private int mStringConversionColumn = -1;
    private CursorToStringConverter mCursorToStringConverter;
    private ViewBinder mViewBinder;
    private String[] mOriginalFrom;

    /**
     * Constructor.
     * 
     * @param context The context where the ListView associated with this
     *            SimpleListItemFactory is running
     * @param layout resource identifier of a layout file that defines the views
     *            for this list item. Thelayout file should include at least
     *            those named views defined in "to"
     * @param c The database cursor.  Can be null if the cursor is not available yet.
     * @param from A list of column names representing the data to bind to the UI.  Can be null 
     *            if the cursor is not available yet.
     * @param to The views that should display column in the "from" parameter.
     *            These should all be TextViews. The first N views in this list
     *            are given the values of the first N columns in the from
     *            parameter.  Can be null if the cursor is not available yet.
     */
    public SimpleCursorAdapter(Context context, int layout, Cursor c, String[] from, int[] to) {
        super(context, layout, c);
        mTo = to;
        mOriginalFrom = from;
        findColumns(from);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        return generateViewHolder(super.newView(context, cursor, parent));
    }

    @Override
    public View newDropDownView(Context context, Cursor cursor, ViewGroup parent) {
        return generateViewHolder(super.newDropDownView(context, cursor, parent));
    }

    private View generateViewHolder(View v) {
        final int[] to = mTo;
        final int count = to.length;
        final View[] holder = new View[count];

        for (int i = 0; i < count; i++) {
            holder[i] = v.findViewById(to[i]);
        }
        v.setTag(holder);

        return v;
    }

    /**
     * Binds all of the field names passed into the "to" parameter of the
     * constructor with their corresponding cursor columns as specified in the
     * "from" parameter.
     *
     * Binding occurs in two phases. First, if a
     * {@link android.widget.SimpleCursorAdapter.ViewBinder} is available,
     * {@link ViewBinder#setViewValue(android.view.View, android.database.Cursor, int)}
     * is invoked. If the returned value is true, binding has occured. If the
     * returned value is false and the view to bind is a TextView,
     * {@link #setViewText(TextView, String)} is invoked. If the returned value is
     * false and the view to bind is an ImageView,
     * {@link #setViewImage(ImageView, String)} is invoked. If no appropriate
     * binding can be found, an {@link IllegalStateException} is thrown.
     *
     * @throws IllegalStateException if binding cannot occur
     * 
     * @see android.widget.CursorAdapter#bindView(android.view.View,
     *      android.content.Context, android.database.Cursor)
     * @see #getViewBinder()
     * @see #setViewBinder(android.widget.SimpleCursorAdapter.ViewBinder)
     * @see #setViewImage(ImageView, String)
     * @see #setViewText(TextView, String)
     */
    @Override
    public void bindView(View view, Context context, Cursor cursor) {
        final View[] holder = (View[]) view.getTag();
        final ViewBinder binder = mViewBinder;
        final int count = mTo.length;
        final int[] from = mFrom;

        for (int i = 0; i < count; i++) {
            final View v = holder[i];
            if (v != null) {
                boolean bound = false;
                if (binder != null) {
                    bound = binder.setViewValue(v, cursor, from[i]);
                }

                if (!bound) {
                    String text = cursor.getString(from[i]);
                    if (text == null) {
                        text = "";
                    }

                    if (v instanceof TextView) {
                        setViewText((TextView) v, text);
                    } else if (v instanceof ImageView) {
                        setViewImage((ImageView) v, text);
                    } else {
                        throw new IllegalStateException(v.getClass().getName() + " is not a " +
                                " view that can be bounds by this SimpleCursorAdapter");
                    }
                }
            }
        }
    }

    /**
     * Returns the {@link ViewBinder} used to bind data to views.
     *
     * @return a ViewBinder or null if the binder does not exist
     *
     * @see #bindView(android.view.View, android.content.Context, android.database.Cursor)
     * @see #setViewBinder(android.widget.SimpleCursorAdapter.ViewBinder)
     */
    public ViewBinder getViewBinder() {
        return mViewBinder;
    }

    /**
     * Sets the binder used to bind data to views.
     *
     * @param viewBinder the binder used to bind data to views, can be null to
     *        remove the existing binder
     *
     * @see #bindView(android.view.View, android.content.Context, android.database.Cursor)
     * @see #getViewBinder()
     */
    public void setViewBinder(ViewBinder viewBinder) {
        mViewBinder = viewBinder;
    }

    /**
     * Called by bindView() to set the image for an ImageView but only if
     * there is no existing ViewBinder or if the existing ViewBinder cannot
     * handle binding to an ImageView.
     *
     * By default, the value will be treated as an image resource. If the
     * value cannot be used as an image resource, the value is used as an
     * image Uri.
     *
     * Intended to be overridden by Adapters that need to filter strings
     * retrieved from the database.
     *
     * @param v ImageView to receive an image
     * @param value the value retrieved from the cursor
     */
    public void setViewImage(ImageView v, String value) {
        try {
            v.setImageResource(Integer.parseInt(value));
        } catch (NumberFormatException nfe) {
            v.setImageURI(Uri.parse(value));
        }
    }

    /**
     * Called by bindView() to set the text for a TextView but only if
     * there is no existing ViewBinder or if the existing ViewBinder cannot
     * handle binding to an TextView.
     *
     * Intended to be overridden by Adapters that need to filter strings
     * retrieved from the database.
     * 
     * @param v TextView to receive text
     * @param text the text to be set for the TextView
     */    
    public void setViewText(TextView v, String text) {
        v.setText(text);
    }

    /**
     * Return the index of the column used to get a String representation
     * of the Cursor.
     *
     * @return a valid index in the current Cursor or -1
     *
     * @see android.widget.CursorAdapter#convertToString(android.database.Cursor)
     * @see #setStringConversionColumn(int) 
     * @see #setCursorToStringConverter(android.widget.SimpleCursorAdapter.CursorToStringConverter)
     * @see #getCursorToStringConverter()
     */
    public int getStringConversionColumn() {
        return mStringConversionColumn;
    }

    /**
     * Defines the index of the column in the Cursor used to get a String
     * representation of that Cursor. The column is used to convert the
     * Cursor to a String only when the current CursorToStringConverter
     * is null.
     *
     * @param stringConversionColumn a valid index in the current Cursor or -1 to use the default
     *        conversion mechanism
     *
     * @see android.widget.CursorAdapter#convertToString(android.database.Cursor)
     * @see #getStringConversionColumn()
     * @see #setCursorToStringConverter(android.widget.SimpleCursorAdapter.CursorToStringConverter)
     * @see #getCursorToStringConverter()
     */
    public void setStringConversionColumn(int stringConversionColumn) {
        mStringConversionColumn = stringConversionColumn;
    }

    /**
     * Returns the converter used to convert the filtering Cursor
     * into a String.
     *
     * @return null if the converter does not exist or an instance of
     *         {@link android.widget.SimpleCursorAdapter.CursorToStringConverter}
     *
     * @see #setCursorToStringConverter(android.widget.SimpleCursorAdapter.CursorToStringConverter)
     * @see #getStringConversionColumn()
     * @see #setStringConversionColumn(int)
     * @see android.widget.CursorAdapter#convertToString(android.database.Cursor)
     */
    public CursorToStringConverter getCursorToStringConverter() {
        return mCursorToStringConverter;
    }

    /**
     * Sets the converter  used to convert the filtering Cursor
     * into a String.
     *
     * @param cursorToStringConverter the Cursor to String converter, or
     *        null to remove the converter
     *
     * @see #setCursorToStringConverter(android.widget.SimpleCursorAdapter.CursorToStringConverter) 
     * @see #getStringConversionColumn()
     * @see #setStringConversionColumn(int)
     * @see android.widget.CursorAdapter#convertToString(android.database.Cursor)
     */
    public void setCursorToStringConverter(CursorToStringConverter cursorToStringConverter) {
        mCursorToStringConverter = cursorToStringConverter;
    }

    /**
     * Returns a CharSequence representation of the specified Cursor as defined
     * by the current CursorToStringConverter. If no CursorToStringConverter
     * has been set, the String conversion column is used instead. If the
     * conversion column is -1, the returned String is empty if the cursor
     * is null or Cursor.toString().
     *
     * @param cursor the Cursor to convert to a CharSequence
     *
     * @return a non-null CharSequence representing the cursor
     */
    @Override
    public CharSequence convertToString(Cursor cursor) {
        if (mCursorToStringConverter != null) {
            return mCursorToStringConverter.convertToString(cursor);
        } else if (mStringConversionColumn > -1) {
            return cursor.getString(mStringConversionColumn);
        }

        return super.convertToString(cursor);
    }

    /**
     * Create a map from an array of strings to an array of column-id integers in mCursor.
     * If mCursor is null, the array will be discarded.
     * 
     * @param from the Strings naming the columns of interest
     */
    private void findColumns(String[] from) {
        if (mCursor != null) {
            int i;
            int count = from.length;
            if (mFrom == null || mFrom.length != count) {
                mFrom = new int[count];
            }
            for (i = 0; i < count; i++) {
                mFrom[i] = mCursor.getColumnIndexOrThrow(from[i]);
            }
        } else {
            mFrom = null;
        }
    }

    @Override
    public void changeCursor(Cursor c) {
        super.changeCursor(c);
        // rescan columns in case cursor layout is different
        findColumns(mOriginalFrom);
    }
    
    /**
     * Change the cursor and change the column-to-view mappings at the same time.
     *  
     * @param c The database cursor.  Can be null if the cursor is not available yet.
     * @param from A list of column names representing the data to bind to the UI.  Can be null 
     *            if the cursor is not available yet.
     * @param to The views that should display column in the "from" parameter.
     *            These should all be TextViews. The first N views in this list
     *            are given the values of the first N columns in the from
     *            parameter.  Can be null if the cursor is not available yet.
     */
    public void changeCursorAndColumns(Cursor c, String[] from, int[] to) {
        mOriginalFrom = from;
        mTo = to;
        super.changeCursor(c);        
        findColumns(mOriginalFrom);
    }

    /**
     * This class can be used by external clients of SimpleCursorAdapter
     * to bind values fom the Cursor to views.
     *
     * You should use this class to bind values from the Cursor to views
     * that are not directly supported by SimpleCursorAdapter or to
     * change the way binding occurs for views supported by
     * SimpleCursorAdapter.
     *
     * @see SimpleCursorAdapter#bindView(android.view.View, android.content.Context, android.database.Cursor)
     * @see SimpleCursorAdapter#setViewImage(ImageView, String) 
     * @see SimpleCursorAdapter#setViewText(TextView, String)
     */
    public static interface ViewBinder {
        /**
         * Binds the Cursor column defined by the specified index to the specified view.
         *
         * When binding is handled by this ViewBinder, this method must return true.
         * If this method returns false, SimpleCursorAdapter will attempts to handle
         * the binding on its own.
         *
         * @param view the view to bind the data to
         * @param cursor the cursor to get the data from
         * @param columnIndex the column at which the data can be found in the cursor
         *
         * @return true if the data was bound to the view, false otherwise
         */
        boolean setViewValue(View view, Cursor cursor, int columnIndex);
    }

    /**
     * This class can be used by external clients of SimpleCursorAdapter
     * to define how the Cursor should be converted to a String.
     *
     * @see android.widget.CursorAdapter#convertToString(android.database.Cursor)
     */
    public static interface CursorToStringConverter {
        /**
         * Returns a CharSequence representing the specified Cursor.
         *
         * @param cursor the cursor for which a CharSequence representation
         *        is requested
         *
         * @return a non-null CharSequence representing the cursor
         */
        CharSequence convertToString(Cursor cursor);
    }

}