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UITableView(Inserting and Deleting Rows and Sections)

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InsertingandDeletingRowsandSections

Atableviewhasaneditingmodeaswellasitsnormal(selection)mode.Whenatableviewgoesintoeditingmode,itdisplaystheeditingandreorderingcontrolsassociatedwithitsrows.Theeditingcontrols,whichareintheleftsideoftherow,allowthe
usertoinsertanddeleterowsinthetableview.Theeditingcontrolshavedistinctiveappearances:

	Deletioncontrol
	Insertioncontrol

Whenatableviewenterseditingmodeandwhenusersclickaneditingcontrol,thetableviewsendsaseriesofmessagestoitsdatasourceanddelegate,butonlyiftheyimplementthesemethods.
Thesemethodsallowthedatasourceanddelegatetorefinetheappearanceandbehaviorofrowsinthetableview;themessagesalsoenablethemtocarryoutthedeletionorinsertionoperation.

Evenifatableviewisnotineditingmode,youcaninsertordeleteanumberofrowsorsectionsasagroupandhavethoseoperationsanimated.

Thefirstsectionbelowshowsyouhow,whenatableisineditingmode,toinsertnewrowsanddeleteexistingrowsinatableviewinresponsetouseractions.Thesecondsection,“Batch
Insertion,Deletion,andReloadingofRowsandSections,”discusseshowyoucaninsertanddeletemultiplesectionsandrowsanimatedasagroup.

Note:Theprocedureforreorderingrowswhenineditingmodeisdescribedin“Managing
theReorderingofRows.”

InsertingandDeletingRowsinEditingMode

WhenaTableViewisEdited

Atableviewgoesintoeditingmodewhenitreceivesa

setEditing:animated:

message.
Typically(butnotnecessarily)themessageoriginatesasanactionmessagesentwhentheusertapsanEditbuttoninthenavigationbar.Ineditingmode,atableviewdisplaysanyediting(andreordering)controlsthatitsdelegatehas
assignedtoeachrow.Thedelegateassignsthecontrolsasaresultofreturningtheeditingstyleforarowinthe

tableView:editingStyleForRowAtIndexPath:

method.

Note:Ifa

UIViewController

object
ismanagingthetableview,itautomaticallyreceivesa

setEditing:animated:

messagewhentheEditbuttonistapped.Initsimplementationofthismessage,itcanupdatebutton
stateordoanyotherkindoftaskbeforeinvokingthetableview’sversionofthemethod.

Whenthetableviewreceives

setEditing:animated:

,
itsendsthesamemessagetothe

UITableViewCell

object
foreachvisiblerow.Thenitsendsasuccessionofmessagestoitsdatasourceanditsdelegate(iftheyimplementthemethods)asdepictedinthediagraminFigure
7-1.
Figure7-1Callingsequencefor
insertingordeletingrowsinatableview

Afterresending

setEditing:animated:

to
thecellscorrespondingtothevisiblerows,thesequenceofmessagesisasfollows:

Thetableviewinvokesthe

tableView:canEditRowAtIndexPath:

method
ifitsdatasourceimplementsit.Thismethodallowstheapplicationtoexcluderowsinthetableviewfrombeingeditedevenwhentheircell’s

editingStyle

property
indicatesotherwise.Mostapplicationsdonotneedtoimplementthismethod.

Thetableviewinvokesthe

tableView:editingStyleForRowAtIndexPath:

method
ifitsdelegateimplementsit.Thismethodallowstheapplicationtospecifyarow’seditingstyleandthustheeditingcontrolthattherowdisplays.
Atthispoint,thetableviewisfullyineditingmode.Itdisplaystheinsertionordeletioncontrolforeacheligiblerow.

Theusertapsaneditingcontrol(eitherthedeletioncontrolortheinsertioncontrol).Ifheorshetapsadeletioncontrol,aDeletebuttonisdisplayedontherow.Theuserthentapsthat
buttontoconfirmthedeletion.

Thetableviewsendsthe

tableView:commitEditingStyle:forRowAtIndexPath:

message
tothedatasource.Althoughthisprotocolmethodismarkedasoptional,thedatasourcemustimplementitifitwantstoinsertordeletearow.Itmustdotwothings:

Send

deleteRowsAtIndexPaths:withRowAnimation:

insertRowsAtIndexPaths:withRowAnimation:

to
thetableviewtodirectittoadjustitspresentation.

Updatethecorrespondingdata-modelarraybyeitherdeletingthereferenceditemfromthearrayoraddinganitemtothearray.

WhentheuserswipesacrossarowtodisplaytheDeletebuttonforthatrow,thereisavariationinthecallingsequencediagrammedinFigure
7-1.Whentheuserswipesarowtodeleteit,thetableviewfirstcheckstoseeifitsdatasourcehasimplementedthe

tableView:commitEditingStyle:forRowAtIndexPath:

method;
ifthatisso,itsends

setEditing:animated:

to
itselfandenterseditingmode.Inthis“swipetodelete”mode,thetableviewdoesnotdisplaytheeditingandreorderingcontrols.Becausethisisauser-drivenevent,italsobracketsthemessagestothedelegateinsideoftwoothermessages:

tableView:willBeginEditingRowAtIndexPath:

and

tableView:didEndEditingRowAtIndexPath:

.
Byimplementingthesemethods,thedelegatecanupdatetheappearanceofthetableviewappropriately.

Note:Thedatasourceshouldnotcall

setEditing:animated:

fromwithinitsimplementationof

tableView:commitEditingStyle:forRowAtIndexPath:

.
Ifforsomereasonitmust,itshouldinvokeitafteradelaybyusingthe

performSelector:withObject:afterDelay:

method.

Althoughyoucanuseaninsertioncontrolasthetriggertoinsertanewrowinatableview,analternativeapproachistohaveanAdd(orplussign)buttoninthenavigationbar.Tappingthebuttonsendsan
actionmessagetotheviewcontroller,whichoverlaysthetableviewwithamodalviewforenteringthenewitem.Oncetheitemisentered,thecontrolleraddsittothedata-modelarrayandreloadsthetable.“An
ExampleofAddingaTable-ViewRow”discussesthisapproach.

AnExampleofDeletingaTable-ViewRow

Thissectiongivesaguidedtourthroughthepartsofaprojectthatworktogethertosetupatableviewforeditingmodeanddeleterowsfromit.Thisprojectusesthenavigationcontrollerandview
controllerarchitecturetomanageitstableviews.Inits

loadView

method,
thecustomviewcontrollercreatesthetableviewandsetsitselftobethedatasourceanddelegate.ItalsosetstherightitemofthenavigationbartobethestandardEditbutton.

self.navigationItem.rightBarButtonItem=self.editButtonItem;

Thisbuttonispreconfiguredtosend

setEditing:animated:

to
theviewcontrollerwhentapped;ittogglesthebuttontitle(betweenEditandDone)andtheBooleaneditingparameteronalternatingtaps.Initsimplementationofthemethod,asshowninListing
7-1,theviewcontrollerinvokesthesuperclassinvocationofthemethod,sendsthesamemessagetothetableview,andupdatestheenabledstateoftheotherbuttoninthenavigationbar(aplus-signbutton,foraddingitems).

Listing7-1Viewcontrollerrespondingto

setEditing:animated:

-(void)setEditing:(BOOL)editinganimated:(BOOL)animated{

[supersetEditing:editinganimated:animated];

[tableViewsetEditing:editinganimated:YES];

if(editing){

addButton.enabled=NO;

}else{

addButton.enabled=YES;

Whenitstableviewenterseditingmode,theviewcontrollerspecifiesadeletioncontrolforeveryrowexceptthelast,whichhasaninsertioncontrol.Itdoesthisinitsimplementationofthe

tableView:editingStyleForRowAtIndexPath:

method
(Listing7-2).

Listing7-2Customizingtheeditingstyleofrows

-(UITableViewCellEditingStyle)tableView:(UITableView*)tableVieweditingStyleForRowAtIndexPath:(NSIndexPath*)indexPath{

SimpleEditableListAppDelegate*controller=(SimpleEditableListAppDelegate*)[[UIApplicationsharedApplication]delegate];

if(indexPath.row==[controllercountOfList]-1){

returnUITableViewCellEditingStyleInsert;

}else{

returnUITableViewCellEditingStyleDelete;

Theusertapsthedeletioncontrolinarowandtheviewcontrollerreceivesa

tableView:commitEditingStyle:forRowAtIndexPath:

message
fromthetableview.AsshowninListing7-3,ithandlesthismessagebyremovingtheitemcorrespondingtotherowfromamodelarray
andsending

deleteRowsAtIndexPaths:withRowAnimation:

to
thetableview.

Listing7-3Updatingthedata-modelarrayanddeletingtherow

-(void)tableView:(UITableView*)tableViewcommitEditingStyle:(UITableViewCellEditingStyle)editingStyleforRowAtIndexPath:(NSIndexPath*)indexPath{

//Ifrowisdeleted,removeitfromthelist.

if(editingStyle==UITableViewCellEditingStyleDelete){

SimpleEditableListAppDelegate*controller=(SimpleEditableListAppDelegate*)[[UIApplicationsharedApplication]delegate];

[controllerremoveObjectFromListAtIndex:indexPath.row];

[tableViewdeleteRowsAtIndexPaths:[NSArrayarrayWithObject:indexPath]withRowAnimation:UITableViewRowAnimationFade];

AnExampleofAddingaTable-ViewRow

Thissectionshowsprojectcodethatinsertsarowinatableview.Insteadofusingtheinsertioncontrolasthetriggerforinsertingarow,itusesanAddbutton(visuallyaplussign)inthenavigationbar
abovethetableview.Thiscodealsoisbasedonthenavigationcontrollerandviewcontrollerarchitecture.Inits

loadView

method
implementation,theviewcontrollerassignstheAddbuttonastheright-sideitemofthenavigationbarusingthecodeshowninListing7-4.

Listing7-4AddinganAddbuttontothenavigationbar

addButton=[[UIBarButtonItemalloc]initWithBarButtonSystemItem:UIBarButtonSystemItemAddtarget:selfaction:@selector(addItem:)];

self.navigationItem.rightBarButtonItem=addButton;

Notethattheviewcontrollersetsthecontrolstatesforthetitleaswellastheactionselectorandthetargetobject.WhentheusertapstheAdd
button,the

addItem:

messageissenttothetarget(theviewcontroller).ItrespondsasshowninListing
7-5.Itcreatesanavigationcontrollerwithasingleviewcontrollerwhoseviewisputonscreenmodally—itanimatesupwardtooverlaythetableview.The

presentModalViewController:animated:

method
todothis.

Listing7-5RespondingtoatapontheAddbutton

-(void)addItem:sender{

if(itemInputController==nil){

itemInputController=[[ItemInputControlleralloc]init];

UINavigationController*navigationController=[[UINavigationControlleralloc]initWithRootViewController:itemInputController];

[[selfnavigationController]presentModalViewController:navigationControlleranimated:YES];

[navigationControllerrelease];

Themodal,oroverlay,viewconsistsofasinglecustomtextfield.Theuserenterstextforthenewtable-viewitemandthentapsaSavebutton.Thisbuttonsendsa

save:

action
messagetoitstarget:theviewcontrollerforthemodalview.AsshowninListing7-6,theviewcontrollerextractsthestringvalue
fromthetextfieldandupdatestheapplication’sdata-modelarraywithit.

Listing7-6Addingthenewitemtothedata-modelarray

-(void)save:sender{

UITextField*textField=[(EditableTableViewTextField*)[tableViewcellForRowAtIndexPath:[NSIndexPathindexPathForRow:0inSection:0]]textField];

SimpleEditableListAppDelegate*controller=(SimpleEditableListAppDelegate*)[[UIApplicationsharedApplication]delegate];

NSString*newItem=textField.text;

if(newItem!=nil){

[controllerinsertObject:newIteminListAtIndex:[controllercountOfList]];

[selfdismissModalViewControllerAnimated:YES];

Afterthemodalviewisdismissedthetableviewisreloaded,anditnowreflectstheaddeditem.

BatchInsertion,Deletion,andReloadingofRowsandSections

The

UITableView

class
allowsyoutoinsert,delete,andreloadagroupofrowsorsectionsatonetime,animatingtheoperationssimultaneouslyinspecifiedways.TheeightmethodsshowninListing
7-7pertaintobatchinsertionanddeletion.Notethatyoucancalltheseinsertionanddeletionmethodsoutsideofananimationblock(asyoudointhedatasourcemethod

tableView:commitEditingStyle:forRowAtIndexPath:

as
discussedin“Inserting
andDeletingRowsinEditingMode”).

Listing7-7Batchinsertionanddeletionmethods

-(void)beginUpdates;

-(void)endUpdates;

-(void)insertSections:(NSIndexSet*)sectionswithRowAnimation:(UITableViewRowAnimation)animation;

-(void)deleteSections:(NSIndexSet*)sectionswithRowAnimation:(UITableViewRowAnimation)animation;

-(void)reloadSections:(NSIndexSet*)sectionswithRowAnimation:(UITableViewRowAnimation)animation;

-(void)insertRowsAtIndexPaths:(NSArray*)indexPathswithRowAnimation:(UITableViewRowAnimation)animation;

-(void)deleteRowsAtIndexPaths:(NSArray*)indexPathswithRowAnimation:(UITableViewRowAnimation)animation;

-(void)reloadRowsAtIndexPaths:(NSArray*)indexPathswithRowAnimation:(UITableViewRowAnimation)animation;

Note:The

reloadSections:withRowAnimation:

and

reloadRowsAtIndexPaths:withRowAnimation:

methods,
whichwereintroducediniOS3.0,allowyoutorequestthetableviewtoreloadthedataforspecificsectionsandrowsinsteadofloadingtheentirevisibletableviewbycalling

reloadData

.

Toanimateabatchinsertion,deletion,andreloadingofrowsandsections,callthecorrespondingmethodswithinananimationblockdefinedbysuccessivecallsto

beginUpdates

and

endUpdates

.
Ifyoudon’tcalltheinsertion,deletion,andreloadingmethodswithinthisblock,rowandsectionindexesmaybeinvalid.Callsto

beginUpdates

and

endUpdates

can
benested;allindexesaretreatedasiftherewereonlytheouterupdateblock.
Attheconclusionofablock—thatis,after

endUpdates

returns—thetableviewqueriesitsdata
sourceanddelegateasusualforrowandsectiondata.Thusthecollectionobjectsbackingthetableviewshouldbeupdatedtoreflecttheneworremovedrowsorsections.

AnExampleofBatchedInsertionandDeletionOperations

Toinsertanddeleteagroupofrowsandsectionsinatableview,firstpreparethearray(orarrays)thatarethesourceofdataforthesectionsandrows.Afterrowsandsectionsaredeletedandinserted,
theresultingrowsandsectionsarepopulatedfromthisdatastore.
Next,callthe

beginUpdates

method,
followedbyinvocationsof

insertRowsAtIndexPaths:withRowAnimation:

deleteRowsAtIndexPaths:withRowAnimation:

insertSections:withRowAnimation:

,
or

deleteSections:withRowAnimation:

.
Concludetheanimationblockbycalling

endUpdates

.Listing
7-8illustratesthisprocedure.

Listing7-8Insertinganddeletingablockofrowsinatableview

-(IBAction)insertAndDeleteRows:(id)sender{

//originalrows:Arizona,California,Delaware,NewJersey,Washington

[statesremoveObjectAtIndex:4];//Washington

[statesremoveObjectAtIndex:2];//Delaware

[statesinsertObject:@"Alaska"atIndex:0];

[statesinsertObject:@"Georgia"atIndex:3];

[statesinsertObject:@"Virginia"atIndex:5];

NSArray*deleteIndexPaths=[NSArrayarrayWithObjects:

[NSIndexPathindexPathForRow:2inSection:0],

[NSIndexPathindexPathForRow:4inSection:0],

nil];

NSArray*insertIndexPaths=[NSArrayarrayWithObjects:

[NSIndexPathindexPathForRow:0inSection:0],

[NSIndexPathindexPathForRow:3inSection:0],

[NSIndexPathindexPathForRow:5inSection:0],

nil];

UITableView*tv=(UITableView*)self.view;

[tvbeginUpdates];

[tvinsertRowsAtIndexPaths:insertIndexPathswithRowAnimation:UITableViewRowAnimationRight];

[tvdeleteRowsAtIndexPaths:deleteIndexPathswithRowAnimation:UITableViewRowAnimationFade];

[tvendUpdates];

//endingrows:Alaska,Arizona,California,Georgia,NewJersey,Virginia

Thisexampleremovestwostringsfromanarray(andtheircorrespondingrows)andinsertsthreestringsintothearray(alongwiththeircorrespondingrows).Thenextsection,“Ordering
ofOperationsandIndexPaths,”explainsparticularaspectsoftherow(orsection)insertionanddeletionbehavior.

OrderingofOperationsandIndexPaths

YoumighthavenoticedsomethinginthecodeshowninListing7-8thatseemspeculiar.
Thecodecallsthe

deleteRowsAtIndexPaths:withRowAnimation:

method
afteritcalls

insertRowsAtIndexPaths:withRowAnimation:

.
However,thisisnottheorderinwhich

UITableView

completes
theoperations.Itdefersanyinsertionsofrowsorsectionsuntilafterithashandledthedeletionsofrowsorsections.Thetableviewbehavesthesamewaywithreloadingmethodscalledinsideanupdateblock—thereloadtakesplacewithrespecttotheindexes
ofrowsandsectionsbeforetheanimationblockisexecuted.Thisbehaviorhappensregardlessoftheorderingoftheinsertion,deletion,andreloadingmethodcalls.
Deletionandreloadingoperationswithinananimationblockspecifywhichrowsandsectionsintheoriginaltableshouldberemovedorreloaded;insertionsspecifywhichrowsandsectionsshouldbeaddedtothe
resultingtable.Theindexpathsusedtoidentifysectionsandrowsfollowthismodel.Insertingorremovinganiteminamutablearray,ontheotherhand,mayaffectthearrayindexusedforthesuccessiveinsertionorremovaloperation;forexample,ifyou
insertanitematacertainindex,theindexesofallsubsequentitemsinthearrayareincremented.
Anexampleisusefulhere.Sayyouhaveatableviewwiththreesections,eachwiththreerows.Thenyouimplementthefollowinganimationblock:

Beginupdates.

Deleterowatindex1ofsectionatindex0.

Deletesectionatindex1.

Insertrowatindex1ofsectionatindex1.

Endupdates.

Figure7-2illustrateswhattakesplaceaftertheanimationblockconcludes.
Figure7-2Deletionofsectionandrowand
insertionofrow

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