https://source.android.com/ 
/*
 * 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.database;

import android.content.ContentResolver;
import android.net.Uri;
import android.os.Bundle;

import java.io.Closeable;


This interface provides random read-write access to the result set returned
by a database query.


Cursor implementations are not required to be synchronized so code using a Cursor from multiple
threads should perform its own synchronization when using the Cursor.

 Implementations should subclass AbstractCursor. 


/**
 * This interface provides random read-write access to the result set returned
 * by a database query.
 * <p>
 * Cursor implementations are not required to be synchronized so code using a Cursor from multiple
 * threads should perform its own synchronization when using the Cursor.
 * </p><p>
 * Implementations should subclass {@link AbstractCursor}.
 * </p>
 */
public interface Cursor extends Closeable {
    /*
     * Values returned by {@link #getType(int)}.
     * These should be consistent with the corresponding types defined in CursorWindow.h
     */
    
Value returned by getType(int) if the specified column is null 
/** Value returned by {@link #getType(int)} if the specified column is null */
    static final int FIELD_TYPE_NULL = 0;

    
Value returned by getType(int) if the specified column type is integer 
/** Value returned by {@link #getType(int)} if the specified  column type is integer */
    static final int FIELD_TYPE_INTEGER = 1;

    
Value returned by getType(int) if the specified column type is float 
/** Value returned by {@link #getType(int)} if the specified column type is float */
    static final int FIELD_TYPE_FLOAT = 2;

    
Value returned by getType(int) if the specified column type is string 
/** Value returned by {@link #getType(int)} if the specified column type is string */
    static final int FIELD_TYPE_STRING = 3;

    
Value returned by getType(int) if the specified column type is blob 
/** Value returned by {@link #getType(int)} if the specified column type is blob */
    static final int FIELD_TYPE_BLOB = 4;

    
Returns the numbers of rows in the cursor.

Returns:the number of rows in the cursor.
/**
     * Returns the numbers of rows in the cursor.
     *
     * @return the number of rows in the cursor.
     */
    int getCount();

    
Returns the current position of the cursor in the row set.
The value is zero-based. When the row set is first returned the cursor
will be at positon -1, which is before the first row. After the
last row is returned another call to next() will leave the cursor past
the last entry, at a position of count().

Returns:the current cursor position.
/**
     * Returns the current position of the cursor in the row set.
     * The value is zero-based. When the row set is first returned the cursor
     * will be at positon -1, which is before the first row. After the
     * last row is returned another call to next() will leave the cursor past
     * the last entry, at a position of count().
     *
     * @return the current cursor position.
     */
    int getPosition();

    
Move the cursor by a relative amount, forward or backward, from the
current position. Positive offsets move forwards, negative offsets move
backwards. If the final position is outside of the bounds of the result
set then the resultant position will be pinned to -1 or count() depending
on whether the value is off the front or end of the set, respectively.

This method will return true if the requested destination was
reachable, otherwise, it returns false. For example, if the cursor is at
currently on the second entry in the result set and move(-5) is called,
the position will be pinned at -1, and false will be returned.

Params:
  • offset – the offset to be applied from the current position.
Returns:whether the requested move fully succeeded.
/**
     * Move the cursor by a relative amount, forward or backward, from the
     * current position. Positive offsets move forwards, negative offsets move
     * backwards. If the final position is outside of the bounds of the result
     * set then the resultant position will be pinned to -1 or count() depending
     * on whether the value is off the front or end of the set, respectively.
     *
     * <p>This method will return true if the requested destination was
     * reachable, otherwise, it returns false. For example, if the cursor is at
     * currently on the second entry in the result set and move(-5) is called,
     * the position will be pinned at -1, and false will be returned.
     *
     * @param offset the offset to be applied from the current position.
     * @return whether the requested move fully succeeded.
     */
    boolean move(int offset);

    
Move the cursor to an absolute position. The valid
range of values is -1 <= position <= count.

This method will return true if the request destination was reachable, 
otherwise, it returns false.

Params:
  • position – the zero-based position to move to.
Returns:whether the requested move fully succeeded.
/**
     * Move the cursor to an absolute position. The valid
     * range of values is -1 &lt;= position &lt;= count.
     *
     * <p>This method will return true if the request destination was reachable, 
     * otherwise, it returns false.
     *
     * @param position the zero-based position to move to.
     * @return whether the requested move fully succeeded.
     */
    boolean moveToPosition(int position);

    
Move the cursor to the first row.

This method will return false if the cursor is empty.

Returns:whether the move succeeded.
/**
     * Move the cursor to the first row.
     *
     * <p>This method will return false if the cursor is empty.
     *
     * @return whether the move succeeded.
     */
    boolean moveToFirst();

    
Move the cursor to the last row.

This method will return false if the cursor is empty.

Returns:whether the move succeeded.
/**
     * Move the cursor to the last row.
     *
     * <p>This method will return false if the cursor is empty.
     *
     * @return whether the move succeeded.
     */
    boolean moveToLast();

    
Move the cursor to the next row.

This method will return false if the cursor is already past the
last entry in the result set.

Returns:whether the move succeeded.
/**
     * Move the cursor to the next row.
     *
     * <p>This method will return false if the cursor is already past the
     * last entry in the result set.
     *
     * @return whether the move succeeded.
     */
    boolean moveToNext();

    
Move the cursor to the previous row.

This method will return false if the cursor is already before the
first entry in the result set.

Returns:whether the move succeeded.
/**
     * Move the cursor to the previous row.
     *
     * <p>This method will return false if the cursor is already before the
     * first entry in the result set.
     *
     * @return whether the move succeeded.
     */
    boolean moveToPrevious();

    
Returns whether the cursor is pointing to the first row.

Returns:whether the cursor is pointing at the first entry.
/**
     * Returns whether the cursor is pointing to the first row.
     *
     * @return whether the cursor is pointing at the first entry.
     */
    boolean isFirst();

    
Returns whether the cursor is pointing to the last row.

Returns:whether the cursor is pointing at the last entry.
/**
     * Returns whether the cursor is pointing to the last row.
     *
     * @return whether the cursor is pointing at the last entry.
     */
    boolean isLast();

    
Returns whether the cursor is pointing to the position before the first
row.

Returns:whether the cursor is before the first result.
/**
     * Returns whether the cursor is pointing to the position before the first
     * row.
     *
     * @return whether the cursor is before the first result.
     */
    boolean isBeforeFirst();

    
Returns whether the cursor is pointing to the position after the last
row.

Returns:whether the cursor is after the last result.
/**
     * Returns whether the cursor is pointing to the position after the last
     * row.
     *
     * @return whether the cursor is after the last result.
     */
    boolean isAfterLast();

    
Returns the zero-based index for the given column name, or -1 if the column doesn't exist. If you expect the column to exist use getColumnIndexOrThrow(String) instead, which will make the error more clear. 
Params:
  • columnName – the name of the target column.
See Also:
Returns:the zero-based column index for the given column name, or -1 if
the column name does not exist.
/**
     * Returns the zero-based index for the given column name, or -1 if the column doesn't exist.
     * If you expect the column to exist use {@link #getColumnIndexOrThrow(String)} instead, which
     * will make the error more clear.
     *
     * @param columnName the name of the target column.
     * @return the zero-based column index for the given column name, or -1 if
     * the column name does not exist.
     * @see #getColumnIndexOrThrow(String)
     */
    int getColumnIndex(String columnName);

    
Returns the zero-based index for the given column name, or throws IllegalArgumentException if the column doesn't exist. If you're not sure if a column will exist or not use getColumnIndex(String) and check for -1, which is more efficient than catching the exceptions. 
Params:
  • columnName – the name of the target column.
Throws:
See Also:
Returns:the zero-based column index for the given column name
/**
     * Returns the zero-based index for the given column name, or throws
     * {@link IllegalArgumentException} if the column doesn't exist. If you're not sure if
     * a column will exist or not use {@link #getColumnIndex(String)} and check for -1, which
     * is more efficient than catching the exceptions.
     *
     * @param columnName the name of the target column.
     * @return the zero-based column index for the given column name
     * @see #getColumnIndex(String)
     * @throws IllegalArgumentException if the column does not exist
     */
    int getColumnIndexOrThrow(String columnName) throws IllegalArgumentException;

    
Returns the column name at the given zero-based column index.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the column name for the given column index.
/**
     * Returns the column name at the given zero-based column index.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the column name for the given column index.
     */
    String getColumnName(int columnIndex);

    
Returns a string array holding the names of all of the columns in the
result set in the order in which they were listed in the result.

Returns:the names of the columns returned in this query.
/**
     * Returns a string array holding the names of all of the columns in the
     * result set in the order in which they were listed in the result.
     *
     * @return the names of the columns returned in this query.
     */
    String[] getColumnNames();

    
Return total number of columns

Returns:number of columns
/**
     * Return total number of columns
     * @return number of columns 
     */
    int getColumnCount();
    
    
Returns the value of the requested column as a byte array.

The result and whether this method throws an exception when the
column value is null or the column type is not a blob type is
implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as a byte array.
/**
     * Returns the value of the requested column as a byte array.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null or the column type is not a blob type is
     * implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as a byte array.
     */
    byte[] getBlob(int columnIndex);

    
Returns the value of the requested column as a String.

The result and whether this method throws an exception when the
column value is null or the column type is not a string type is
implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as a String.
/**
     * Returns the value of the requested column as a String.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null or the column type is not a string type is
     * implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as a String.
     */
    String getString(int columnIndex);
    
    
Retrieves the requested column text and stores it in the buffer provided.
If the buffer size is not sufficient, a new char buffer will be allocated 
and assigned to CharArrayBuffer.data

Params:
  • columnIndex – the zero-based index of the target column.
       if the target column is null, return buffer
  • buffer – the buffer to copy the text into.
/**
     * Retrieves the requested column text and stores it in the buffer provided.
     * If the buffer size is not sufficient, a new char buffer will be allocated 
     * and assigned to CharArrayBuffer.data
     * @param columnIndex the zero-based index of the target column.
     *        if the target column is null, return buffer
     * @param buffer the buffer to copy the text into. 
     */
    void copyStringToBuffer(int columnIndex, CharArrayBuffer buffer);
    
    
Returns the value of the requested column as a short.

The result and whether this method throws an exception when the
column value is null, the column type is not an integral type, or the
integer value is outside the range [Short.MIN_VALUE,
Short.MAX_VALUE] is implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as a short.
/**
     * Returns the value of the requested column as a short.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null, the column type is not an integral type, or the
     * integer value is outside the range [<code>Short.MIN_VALUE</code>,
     * <code>Short.MAX_VALUE</code>] is implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as a short.
     */
    short getShort(int columnIndex);

    
Returns the value of the requested column as an int.

The result and whether this method throws an exception when the
column value is null, the column type is not an integral type, or the
integer value is outside the range [Integer.MIN_VALUE,
Integer.MAX_VALUE] is implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as an int.
/**
     * Returns the value of the requested column as an int.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null, the column type is not an integral type, or the
     * integer value is outside the range [<code>Integer.MIN_VALUE</code>,
     * <code>Integer.MAX_VALUE</code>] is implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as an int.
     */
    int getInt(int columnIndex);

    
Returns the value of the requested column as a long.

The result and whether this method throws an exception when the
column value is null, the column type is not an integral type, or the
integer value is outside the range [Long.MIN_VALUE,
Long.MAX_VALUE] is implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as a long.
/**
     * Returns the value of the requested column as a long.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null, the column type is not an integral type, or the
     * integer value is outside the range [<code>Long.MIN_VALUE</code>,
     * <code>Long.MAX_VALUE</code>] is implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as a long.
     */
    long getLong(int columnIndex);

    
Returns the value of the requested column as a float.

The result and whether this method throws an exception when the
column value is null, the column type is not a floating-point type, or the
floating-point value is not representable as a float value is
implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as a float.
/**
     * Returns the value of the requested column as a float.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null, the column type is not a floating-point type, or the
     * floating-point value is not representable as a <code>float</code> value is
     * implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as a float.
     */
    float getFloat(int columnIndex);

    
Returns the value of the requested column as a double.

The result and whether this method throws an exception when the
column value is null, the column type is not a floating-point type, or the
floating-point value is not representable as a double value is
implementation-defined.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:the value of that column as a double.
/**
     * Returns the value of the requested column as a double.
     *
     * <p>The result and whether this method throws an exception when the
     * column value is null, the column type is not a floating-point type, or the
     * floating-point value is not representable as a <code>double</code> value is
     * implementation-defined.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return the value of that column as a double.
     */
    double getDouble(int columnIndex);

    
Returns data type of the given column's value. The preferred type of the column is returned but the data may be converted to other types as documented in the get-type methods such as getInt(int), getFloat(int) etc. 

Returned column types are





Params:
  • columnIndex – the zero-based index of the target column.
Returns:column value type
/**
     * Returns data type of the given column's value.
     * The preferred type of the column is returned but the data may be converted to other types
     * as documented in the get-type methods such as {@link #getInt(int)}, {@link #getFloat(int)}
     * etc.
     *<p>
     * Returned column types are
     * <ul>
     *   <li>{@link #FIELD_TYPE_NULL}</li>
     *   <li>{@link #FIELD_TYPE_INTEGER}</li>
     *   <li>{@link #FIELD_TYPE_FLOAT}</li>
     *   <li>{@link #FIELD_TYPE_STRING}</li>
     *   <li>{@link #FIELD_TYPE_BLOB}</li>
     *</ul>
     *</p>
     *
     * @param columnIndex the zero-based index of the target column.
     * @return column value type
     */
    int getType(int columnIndex);

    
Returns true if the value in the indicated column is null.

Params:
  • columnIndex – the zero-based index of the target column.
Returns:whether the column value is null.
/**
     * Returns <code>true</code> if the value in the indicated column is null.
     *
     * @param columnIndex the zero-based index of the target column.
     * @return whether the column value is null.
     */
    boolean isNull(int columnIndex);

    
Deactivates the Cursor, making all calls on it fail until requery is called. Inactive Cursors use fewer resources than active Cursors. Calling requery will make the cursor active again. 
Deprecated:Since requery() is deprecated, so too is this.
/**
     * Deactivates the Cursor, making all calls on it fail until {@link #requery} is called.
     * Inactive Cursors use fewer resources than active Cursors.
     * Calling {@link #requery} will make the cursor active again.
     * @deprecated Since {@link #requery()} is deprecated, so too is this.
     */
    @Deprecated
    void deactivate();

    
Performs the query that created the cursor again, refreshing its contents. This may be done at any time, including after a call to deactivate. Since this method could execute a query on the database and potentially take a while, it could cause ANR if it is called on Main (UI) thread. A warning is printed if this method is being executed on Main thread. 
Returns:true if the requery succeeded, false if not, in which case the
        cursor becomes invalid.
Deprecated:Don't use this. Just request a new cursor, so you can do this
asynchronously and update your list view once the new cursor comes back.
/**
     * Performs the query that created the cursor again, refreshing its 
     * contents. This may be done at any time, including after a call to {@link
     * #deactivate}.
     *
     * Since this method could execute a query on the database and potentially take
     * a while, it could cause ANR if it is called on Main (UI) thread.
     * A warning is printed if this method is being executed on Main thread.
     *
     * @return true if the requery succeeded, false if not, in which case the
     *         cursor becomes invalid.
     * @deprecated Don't use this. Just request a new cursor, so you can do this
     * asynchronously and update your list view once the new cursor comes back.
     */
    @Deprecated
    boolean requery();

    
Closes the Cursor, releasing all of its resources and making it completely invalid. Unlike deactivate() a call to requery() will not make the Cursor valid again. 
/**
     * Closes the Cursor, releasing all of its resources and making it completely invalid.
     * Unlike {@link #deactivate()} a call to {@link #requery()} will not make the Cursor valid
     * again.
     */
    void close();

    
return true if the cursor is closed

Returns:true if the cursor is closed.
/**
     * return true if the cursor is closed
     * @return true if the cursor is closed.
     */
    boolean isClosed();
    
    
Register an observer that is called when changes happen to the content backing this cursor. Typically the data set won't change until requery() is called. 
Params:
  • observer – the object that gets notified when the content backing the cursor changes.
See Also:
/**
     * Register an observer that is called when changes happen to the content backing this cursor.
     * Typically the data set won't change until {@link #requery()} is called.
     *
     * @param observer the object that gets notified when the content backing the cursor changes.
     * @see #unregisterContentObserver(ContentObserver)
     */
    void registerContentObserver(ContentObserver observer);

    
Unregister an observer that has previously been registered with this cursor via registerContentObserver. 
Params:
  • observer – the object to unregister.
See Also:
/**
     * Unregister an observer that has previously been registered with this
     * cursor via {@link #registerContentObserver}.
     *
     * @param observer the object to unregister.
     * @see #registerContentObserver(ContentObserver)
     */
    void unregisterContentObserver(ContentObserver observer);
    
    
Register an observer that is called when changes happen to the contents of the this cursors data set, for example, when the data set is changed via requery(), deactivate(), or close(). 
Params:
  • observer – the object that gets notified when the cursors data set changes.
See Also:
/**
     * Register an observer that is called when changes happen to the contents
     * of the this cursors data set, for example, when the data set is changed via
     * {@link #requery()}, {@link #deactivate()}, or {@link #close()}.
     *
     * @param observer the object that gets notified when the cursors data set changes.
     * @see #unregisterDataSetObserver(DataSetObserver)
     */
    void registerDataSetObserver(DataSetObserver observer);

    
Unregister an observer that has previously been registered with this cursor via registerContentObserver. 
Params:
  • observer – the object to unregister.
See Also:
/**
     * Unregister an observer that has previously been registered with this
     * cursor via {@link #registerContentObserver}.
     *
     * @param observer the object to unregister.
     * @see #registerDataSetObserver(DataSetObserver)
     */
    void unregisterDataSetObserver(DataSetObserver observer);

    
Register to watch a content URI for changes. This can be the URI of a specific data row (for 
example, "content://my_provider_type/23"), or a a generic URI for a content type.

Params:
  • cr – The content resolver from the caller's context. The listener attached to 
this resolver will be notified.
  • uri – The content URI to watch.
/**
     * Register to watch a content URI for changes. This can be the URI of a specific data row (for 
     * example, "content://my_provider_type/23"), or a a generic URI for a content type.
     * 
     * @param cr The content resolver from the caller's context. The listener attached to 
     * this resolver will be notified.
     * @param uri The content URI to watch.
     */
    void setNotificationUri(ContentResolver cr, Uri uri);

    
Return the URI at which notifications of changes in this Cursor's data will be delivered, as previously set by setNotificationUri. 
Returns:Returns a URI that can be used with 
ContentResolver.registerContentObserver to find out about changes to this Cursor's data. May be null if no notification URI has been set.
/**
     * Return the URI at which notifications of changes in this Cursor's data
     * will be delivered, as previously set by {@link #setNotificationUri}.
     * @return Returns a URI that can be used with
     * {@link ContentResolver#registerContentObserver(android.net.Uri, boolean, ContentObserver)
     * ContentResolver.registerContentObserver} to find out about changes to this Cursor's
     * data.  May be null if no notification URI has been set.
     */
    Uri getNotificationUri();

    
onMove() will only be called across processes if this method returns true.

Returns:whether all cursor movement should result in a call to onMove().
/**
     * onMove() will only be called across processes if this method returns true.
     * @return whether all cursor movement should result in a call to onMove().
     */
    boolean getWantsAllOnMoveCalls();

    
Sets a Bundle that will be returned by getExtras(). 
Params:
  • extras – Bundle to set, or null to set an empty bundle.
/**
     * Sets a {@link Bundle} that will be returned by {@link #getExtras()}.
     *
     * @param extras {@link Bundle} to set, or null to set an empty bundle.
     */
    void setExtras(Bundle extras);

    
Returns a bundle of extra values. This is an optional way for cursors to provide out-of-band
metadata to their users. One use of this is for reporting on the progress of network requests
that are required to fetch data for the cursor.

These values may only change when requery is called.

Returns:cursor-defined values, or Bundle.EMPTY if there are no values. Never null.
/**
     * Returns a bundle of extra values. This is an optional way for cursors to provide out-of-band
     * metadata to their users. One use of this is for reporting on the progress of network requests
     * that are required to fetch data for the cursor.
     *
     * <p>These values may only change when requery is called.
     * @return cursor-defined values, or {@link android.os.Bundle#EMPTY Bundle.EMPTY} if there
     *         are no values. Never <code>null</code>.
     */
    Bundle getExtras();

    
This is an out-of-band way for the the user of a cursor to communicate with the cursor. The
structure of each bundle is entirely defined by the cursor.

One use of this is to tell a cursor that it should retry its network request after it
reported an error.

Params:
Returns:extra values, or Bundle.EMPTY. Never null.
/**
     * This is an out-of-band way for the the user of a cursor to communicate with the cursor. The
     * structure of each bundle is entirely defined by the cursor.
     *
     * <p>One use of this is to tell a cursor that it should retry its network request after it
     * reported an error.
     * @param extras extra values, or {@link android.os.Bundle#EMPTY Bundle.EMPTY}.
     *         Never <code>null</code>.
     * @return extra values, or {@link android.os.Bundle#EMPTY Bundle.EMPTY}.
     *         Never <code>null</code>.
     */
    Bundle respond(Bundle extras);
}