AbstractCursor
public
abstract
class
AbstractCursor
extends Object
implements
CrossProcessCursor
java.lang.Object | |
↳ | android.database.AbstractCursor |
This is an abstract cursor class that handles a lot of the common code that all cursors need to deal with and is provided for convenience reasons.
Summary
Nested classes | |
---|---|
class |
AbstractCursor.SelfContentObserver
Cursors use this class to track changes others make to their URI. |
Inherited constants |
---|
Fields | |
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protected
boolean |
mClosed
This field was deprecated
in API level 23.
Use |
protected
ContentResolver |
mContentResolver
This field was deprecated in API level 23. Do not use. |
protected
int |
mPos
This field was deprecated
in API level 23.
Use |
Public constructors | |
---|---|
AbstractCursor()
|
Public methods | |
---|---|
void
|
close()
Closes the Cursor, releasing all of its resources and making it completely invalid. |
void
|
copyStringToBuffer(int columnIndex, CharArrayBuffer buffer)
Retrieves the requested column text and stores it in the buffer provided. |
void
|
deactivate()
Deactivates the Cursor, making all calls on it fail until |
void
|
fillWindow(int position, CursorWindow window)
Copies cursor data into the window. |
byte[]
|
getBlob(int column)
Returns the value of the requested column as a byte array. |
int
|
getColumnCount()
Return total number of columns |
int
|
getColumnIndex(String columnName)
Returns the zero-based index for the given column name, or -1 if the column doesn't exist. |
int
|
getColumnIndexOrThrow(String columnName)
Returns the zero-based index for the given column name, or throws
|
String
|
getColumnName(int columnIndex)
Returns the column name at the given zero-based column index. |
abstract
String[]
|
getColumnNames()
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. |
abstract
int
|
getCount()
Returns the numbers of rows in the cursor. |
abstract
double
|
getDouble(int column)
Returns the value of the requested column as a double. |
Bundle
|
getExtras()
Returns a bundle of extra values. |
abstract
float
|
getFloat(int column)
Returns the value of the requested column as a float. |
abstract
int
|
getInt(int column)
Returns the value of the requested column as an int. |
abstract
long
|
getLong(int column)
Returns the value of the requested column as a long. |
Uri
|
getNotificationUri()
Return the URI at which notifications of changes in this Cursor's data
will be delivered, as previously set by |
List<Uri>
|
getNotificationUris()
Return the URIs at which notifications of changes in this Cursor's data
will be delivered, as previously set by |
final
int
|
getPosition()
Returns the current position of the cursor in the row set. |
abstract
short
|
getShort(int column)
Returns the value of the requested column as a short. |
abstract
String
|
getString(int column)
Returns the value of the requested column as a String. |
int
|
getType(int column)
Returns data type of the given column's value. |
boolean
|
getWantsAllOnMoveCalls()
onMove() will only be called across processes if this method returns true. |
CursorWindow
|
getWindow()
If the cursor is backed by a |
final
boolean
|
isAfterLast()
Returns whether the cursor is pointing to the position after the last row. |
final
boolean
|
isBeforeFirst()
Returns whether the cursor is pointing to the position before the first row. |
boolean
|
isClosed()
return true if the cursor is closed |
final
boolean
|
isFirst()
Returns whether the cursor is pointing to the first row. |
final
boolean
|
isLast()
Returns whether the cursor is pointing to the last row. |
abstract
boolean
|
isNull(int column)
Returns |
final
boolean
|
move(int offset)
Move the cursor by a relative amount, forward or backward, from the current position. |
final
boolean
|
moveToFirst()
Move the cursor to the first row. |
final
boolean
|
moveToLast()
Move the cursor to the last row. |
final
boolean
|
moveToNext()
Move the cursor to the next row. |
final
boolean
|
moveToPosition(int position)
Move the cursor to an absolute position. |
final
boolean
|
moveToPrevious()
Move the cursor to the previous row. |
boolean
|
onMove(int oldPosition, int newPosition)
This function is called every time the cursor is successfully scrolled to a new position, giving the subclass a chance to update any state it may have. |
void
|
registerContentObserver(ContentObserver observer)
Register an observer that is called when changes happen to the content backing this cursor. |
void
|
registerDataSetObserver(DataSetObserver 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
|
boolean
|
requery()
Performs the query that created the cursor again, refreshing its contents. |
Bundle
|
respond(Bundle extras)
This is an out-of-band way for the user of a cursor to communicate with the cursor. |
void
|
setExtras(Bundle extras)
Sets a |
void
|
setNotificationUri(ContentResolver cr, Uri notifyUri)
Specifies a content URI to watch for changes. |
void
|
setNotificationUris(ContentResolver cr, List<Uri> notifyUris)
Similar to |
void
|
unregisterContentObserver(ContentObserver observer)
Unregister an observer that has previously been registered with this
cursor via |
void
|
unregisterDataSetObserver(DataSetObserver observer)
Unregister an observer that has previously been registered with this
cursor via |
Protected methods | |
---|---|
void
|
checkPosition()
This function throws CursorIndexOutOfBoundsException if the cursor position is out of bounds. |
void
|
finalize()
Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. |
Object
|
getUpdatedField(int columnIndex)
This method was deprecated in API level 15. Always returns null since Cursors do not support updating rows |
boolean
|
isFieldUpdated(int columnIndex)
This method was deprecated in API level 15. Always returns false since Cursors do not support updating rows |
void
|
onChange(boolean selfChange)
Subclasses must call this method when they finish committing updates to notify all observers. |
Inherited methods | |
---|---|
Fields
mClosed
protected boolean mClosed
This field was deprecated
in API level 23.
Use isClosed()
instead.
mContentResolver
protected ContentResolver mContentResolver
This field was deprecated
in API level 23.
Do not use.
Public constructors
Public methods
close
public void close ()
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.
copyStringToBuffer
public void copyStringToBuffer (int columnIndex, CharArrayBuffer buffer)
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
Parameters | |
---|---|
columnIndex |
int : the zero-based index of the target column.
if the target column is null, return buffer
Value is 0 or greater |
buffer |
CharArrayBuffer : the buffer to copy the text into. |
deactivate
public void deactivate ()
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.
fillWindow
public void fillWindow (int position, CursorWindow window)
Copies cursor data into the window.
Clears the window and fills it with data beginning at the requested row position until all of the data in the cursor is exhausted or the window runs out of space.
The filled window uses the same row indices as the original cursor. For example, if you fill a window starting from row 5 from the cursor, you can query the contents of row 5 from the window just by asking it for row 5 because there is a direct correspondence between the row indices used by the cursor and the window.
The current position of the cursor, as returned by Cursor.getPosition()
,
is not changed by this method.
Parameters | |
---|---|
position |
int : The zero-based index of the first row to copy into the window. |
window |
CursorWindow : The window to fill. |
getBlob
public byte[] getBlob (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
byte[] |
the value of that column as a byte array. |
getColumnCount
public int getColumnCount ()
Return total number of columns
Returns | |
---|---|
int |
number of columns Value is 0 or greater |
getColumnIndex
public int getColumnIndex (String columnName)
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(java.lang.String)
instead, which
will make the error more clear.
Parameters | |
---|---|
columnName |
String : the name of the target column. |
Returns | |
---|---|
int |
the zero-based column index for the given column name, or -1 if the column name does not exist. Value is -1 or greater |
getColumnIndexOrThrow
public int getColumnIndexOrThrow (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(java.lang.String)
and check for -1, which
is more efficient than catching the exceptions.
Parameters | |
---|---|
columnName |
String : the name of the target column. |
Returns | |
---|---|
int |
the zero-based column index for the given column name Value is 0 or greater |
getColumnName
public String getColumnName (int columnIndex)
Returns the column name at the given zero-based column index.
Parameters | |
---|---|
columnIndex |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
String |
the column name for the given column index. |
getColumnNames
public abstract String[] getColumnNames ()
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 | |
---|---|
String[] |
the names of the columns returned in this query. |
getCount
public abstract int getCount ()
Returns the numbers of rows in the cursor.
Returns | |
---|---|
int |
the number of rows in the cursor. Value is 0 or greater |
getDouble
public abstract double getDouble (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
double |
the value of that column as a double. |
getExtras
public Bundle getExtras ()
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 | |
---|---|
Bundle |
cursor-defined values, or Bundle.EMPTY if there
are no values. Never null . |
getFloat
public abstract float getFloat (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
float |
the value of that column as a float. |
getInt
public abstract int getInt (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
int |
the value of that column as an int. |
getLong
public abstract long getLong (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
long |
the value of that column as a long. |
getNotificationUri
public Uri getNotificationUri ()
Return the URI at which notifications of changes in this Cursor's data
will be delivered, as previously set by setNotificationUri(ContentResolver, Uri)
.
Returns | |
---|---|
Uri |
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. |
getNotificationUris
public List<Uri> getNotificationUris ()
Return the URIs at which notifications of changes in this Cursor's data
will be delivered, as previously set by setNotificationUris(ContentResolver, List)
.
If this is not implemented, this is equivalent to calling getNotificationUri()
.
Returns | |
---|---|
List<Uri> |
Returns URIs 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. |
getPosition
public final int getPosition ()
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 | |
---|---|
int |
the current cursor position. Value is -1 or greater |
getShort
public abstract short getShort (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
short |
the value of that column as a short. |
getString
public abstract String getString (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
String |
the value of that column as a String. |
getType
public int getType (int column)
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.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
int |
column value type
Value is FIELD_TYPE_NULL , FIELD_TYPE_INTEGER , FIELD_TYPE_FLOAT , FIELD_TYPE_STRING , or FIELD_TYPE_BLOB |
getWantsAllOnMoveCalls
public boolean getWantsAllOnMoveCalls ()
onMove() will only be called across processes if this method returns true.
Returns | |
---|---|
boolean |
whether all cursor movement should result in a call to onMove(). |
getWindow
public CursorWindow getWindow ()
If the cursor is backed by a CursorWindow
, returns a pre-filled
window with the contents of the cursor, otherwise null.
Returns | |
---|---|
CursorWindow |
The pre-filled window that backs this cursor, or null if none. |
isAfterLast
public final boolean isAfterLast ()
Returns whether the cursor is pointing to the position after the last row.
Returns | |
---|---|
boolean |
whether the cursor is after the last result. |
isBeforeFirst
public final boolean isBeforeFirst ()
Returns whether the cursor is pointing to the position before the first row.
Returns | |
---|---|
boolean |
whether the cursor is before the first result. |
isClosed
public boolean isClosed ()
return true if the cursor is closed
Returns | |
---|---|
boolean |
true if the cursor is closed. |
isFirst
public final boolean isFirst ()
Returns whether the cursor is pointing to the first row.
Returns | |
---|---|
boolean |
whether the cursor is pointing at the first entry. |
isLast
public final boolean isLast ()
Returns whether the cursor is pointing to the last row.
Returns | |
---|---|
boolean |
whether the cursor is pointing at the last entry. |
isNull
public abstract boolean isNull (int column)
Returns true
if the value in the indicated column is null.
Parameters | |
---|---|
column |
int : the zero-based index of the target column.
Value is 0 or greater |
Returns | |
---|---|
boolean |
whether the column value is null. |
move
public final boolean move (int offset)
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.
Parameters | |
---|---|
offset |
int : the offset to be applied from the current position. |
Returns | |
---|---|
boolean |
whether the requested move fully succeeded. |
moveToFirst
public final boolean moveToFirst ()
Move the cursor to the first row.
This method will return false if the cursor is empty.
Returns | |
---|---|
boolean |
whether the move succeeded. |
moveToLast
public final boolean moveToLast ()
Move the cursor to the last row.
This method will return false if the cursor is empty.
Returns | |
---|---|
boolean |
whether the move succeeded. |
moveToNext
public final boolean moveToNext ()
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 | |
---|---|
boolean |
whether the move succeeded. |
moveToPosition
public final boolean moveToPosition (int position)
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.
Parameters | |
---|---|
position |
int : the zero-based position to move to.
Value is -1 or greater |
Returns | |
---|---|
boolean |
whether the requested move fully succeeded. |
moveToPrevious
public final boolean moveToPrevious ()
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 | |
---|---|
boolean |
whether the move succeeded. |
onMove
public boolean onMove (int oldPosition, int newPosition)
This function is called every time the cursor is successfully scrolled to a new position, giving the subclass a chance to update any state it may have. If it returns false the move function will also do so and the cursor will scroll to the beforeFirst position.
Parameters | |
---|---|
oldPosition |
int : the position that we're moving from |
newPosition |
int : the position that we're moving to |
Returns | |
---|---|
boolean |
true if the move is successful, false otherwise |
registerContentObserver
public void registerContentObserver (ContentObserver observer)
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.
Parameters | |
---|---|
observer |
ContentObserver : the object that gets notified when the content backing the cursor changes. |
registerDataSetObserver
public void registerDataSetObserver (DataSetObserver 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()
.
Parameters | |
---|---|
observer |
DataSetObserver : the object that gets notified when the cursors data set changes. |
requery
public boolean requery ()
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 | |
---|---|
boolean |
true if the requery succeeded, false if not, in which case the cursor becomes invalid. |
respond
public Bundle respond (Bundle extras)
This is an out-of-band way for 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.
Parameters | |
---|---|
extras |
Bundle : extra values, or Bundle.EMPTY .
Never null . |
Returns | |
---|---|
Bundle |
extra values, or Bundle.EMPTY .
Never null . |
setExtras
public void setExtras (Bundle extras)
Sets a Bundle
that will be returned by getExtras()
.
Parameters | |
---|---|
extras |
Bundle : Bundle to set, or null to set an empty bundle. |
setNotificationUri
public void setNotificationUri (ContentResolver cr, Uri notifyUri)
Specifies a content URI to watch for changes.
Parameters | |
---|---|
cr |
ContentResolver : The content resolver from the caller's context. |
notifyUri |
Uri : The URI to watch for changes. This can be a
specific row URI, or a base URI for a whole class of content. |
setNotificationUris
public void setNotificationUris (ContentResolver cr, List<Uri> notifyUris)
Similar to setNotificationUri(android.content.ContentResolver, android.net.Uri)
, except this version allows
to watch multiple content URIs for changes.
If this is not implemented, this is equivalent to calling
setNotificationUri(android.content.ContentResolver, android.net.Uri)
with the first URI in uris
.
Calling this overrides any previous call to
setNotificationUri(android.content.ContentResolver, android.net.Uri)
.
Parameters | |
---|---|
cr |
ContentResolver : This value cannot be null . |
notifyUris |
List : This value cannot be null . |
unregisterContentObserver
public void unregisterContentObserver (ContentObserver observer)
Unregister an observer that has previously been registered with this
cursor via registerContentObserver(ContentObserver)
.
Parameters | |
---|---|
observer |
ContentObserver : the object to unregister. |
unregisterDataSetObserver
public void unregisterDataSetObserver (DataSetObserver observer)
Unregister an observer that has previously been registered with this
cursor via registerContentObserver(ContentObserver)
.
Parameters | |
---|---|
observer |
DataSetObserver : the object to unregister. |
Protected methods
checkPosition
protected void checkPosition ()
This function throws CursorIndexOutOfBoundsException if the cursor position is out of bounds. Subclass implementations of the get functions should call this before attempting to retrieve data.
Throws | |
---|---|
|
android.database.CursorIndexOutOfBoundsException |
finalize
protected void finalize ()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
A subclass overrides the finalize
method to dispose of
system resources or to perform other cleanup.
The general contract of finalize
is that it is invoked
if and when the Java virtual
machine has determined that there is no longer any
means by which this object can be accessed by any thread that has
not yet died, except as a result of an action taken by the
finalization of some other object or class which is ready to be
finalized. The finalize
method may take any action, including
making this object available again to other threads; the usual purpose
of finalize
, however, is to perform cleanup actions before
the object is irrevocably discarded. For example, the finalize method
for an object that represents an input/output connection might perform
explicit I/O transactions to break the connection before the object is
permanently discarded.
The finalize
method of class Object
performs no
special action; it simply returns normally. Subclasses of
Object
may override this definition.
The Java programming language does not guarantee which thread will
invoke the finalize
method for any given object. It is
guaranteed, however, that the thread that invokes finalize will not
be holding any user-visible synchronization locks when finalize is
invoked. If an uncaught exception is thrown by the finalize method,
the exception is ignored and finalization of that object terminates.
After the finalize
method has been invoked for an object, no
further action is taken until the Java virtual machine has again
determined that there is no longer any means by which this object can
be accessed by any thread that has not yet died, including possible
actions by other objects or classes which are ready to be finalized,
at which point the object may be discarded.
The finalize
method is never invoked more than once by a Java
virtual machine for any given object.
Any exception thrown by the finalize
method causes
the finalization of this object to be halted, but is otherwise
ignored.
getUpdatedField
protected Object getUpdatedField (int columnIndex)
This method was deprecated
in API level 15.
Always returns null since Cursors do not support updating rows
Parameters | |
---|---|
columnIndex |
int |
Returns | |
---|---|
Object |
isFieldUpdated
protected boolean isFieldUpdated (int columnIndex)
This method was deprecated
in API level 15.
Always returns false since Cursors do not support updating rows
Parameters | |
---|---|
columnIndex |
int |
Returns | |
---|---|
boolean |
onChange
protected void onChange (boolean selfChange)
Subclasses must call this method when they finish committing updates to notify all observers.
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Last updated 2024-06-18 UTC.