RootViewController.m
/* |
File: RootViewController.m |
Abstract: The table view controller responsible for displaying information about a book. |
The user can also edit the information. When editing starts, the root view controller |
creates an undo manager to record changes. The undo manager supports up to three levels |
of and redo. When the user taps Done, changes are considered to be committed and the |
undo manager is disposed of. |
Version: 1.2 |
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*/ |
#import "RootViewController.h" |
#import "EditingViewController.h" |
#import "Book.h" |
@interface RootViewController () |
@property (nonatomic, strong) NSDateFormatter *dateFormatter; |
@property (nonatomic, strong) NSUndoManager *undoManager; |
@end |
@implementation RootViewController |
// Must explicitly synthesize this. |
@synthesize undoManager; |
#pragma mark - View lifecycle |
// ------------------------------------------------------------------------------- |
// viewDidLoad |
// ------------------------------------------------------------------------------- |
- (void)viewDidLoad |
{ |
[super viewDidLoad]; |
// UIViewController provides a pre-configured edit button that toggles its |
// title and associated state between Edit and Done. |
// -setEditing:animated: will be called when the user taps this button. |
self.navigationItem.rightBarButtonItem = self.editButtonItem; |
} |
// ------------------------------------------------------------------------------- |
// viewWillAppear: |
// ------------------------------------------------------------------------------- |
- (void)viewWillAppear:(BOOL)animated |
{ |
[super viewWillAppear:animated]; |
// Redisplay the data. |
[self.tableView reloadData]; |
} |
// ------------------------------------------------------------------------------- |
// viewDidAppear: |
// ------------------------------------------------------------------------------- |
- (void)viewDidAppear:(BOOL)animated |
{ |
[super viewDidAppear:animated]; |
// We must be the first responder to receive shake events for undo. |
[self becomeFirstResponder]; |
} |
// ------------------------------------------------------------------------------- |
// viewWillDisappear: |
// ------------------------------------------------------------------------------- |
- (void)viewWillDisappear:(BOOL)animated |
{ |
[super viewWillDisappear:animated]; |
// You should resign first responder status when exiting the screen. |
[self resignFirstResponder]; |
} |
// ------------------------------------------------------------------------------- |
// didReceiveMemoryWarning |
// ------------------------------------------------------------------------------- |
- (void)didReceiveMemoryWarning |
{ |
[super didReceiveMemoryWarning]; |
// Release any properties that can be recreated lazily. |
self.dateFormatter = nil; |
} |
#pragma mark - Rotation |
#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_6_0 |
// ------------------------------------------------------------------------------- |
// shouldAutorotateToInterfaceOrientation: |
// Disable rotation on iOS 5.x and earlier. Note, for iOS 6.0 and later all you |
// need is "UISupportedInterfaceOrientations" defined in your Info.plist |
// ------------------------------------------------------------------------------- |
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation |
{ |
return (interfaceOrientation == UIInterfaceOrientationPortrait); |
} |
#endif |
#pragma mark - UITableViewDataSource |
// Standard table view data source and delegate methods to display a table view |
// containing a single section with three rows showing different properties of the |
// book. |
// ------------------------------------------------------------------------------- |
// tableView:numberOfRowsInSection: |
// There are three rows, corresponding to the three pieces of information |
// the user can edit for a Book object. |
// ------------------------------------------------------------------------------- |
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section |
{ |
return 3; |
} |
// ------------------------------------------------------------------------------- |
// tableView:cellForRowAtIndexPath: |
// ------------------------------------------------------------------------------- |
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath |
{ |
static NSString *CellIdentifier = @"Cell"; |
// Dequeue and then configure a table cell for each attribute of the book. |
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; |
switch (indexPath.row) { |
case 0: // Title |
cell.textLabel.text = @"Title"; |
cell.detailTextLabel.text = self.book.title; |
break; |
case 1: // Author |
cell.textLabel.text = @"Author"; |
cell.detailTextLabel.text = self.book.author; |
break; |
case 2: // Copyright |
cell.textLabel.text = @"Copyright"; |
cell.detailTextLabel.text = [self.dateFormatter stringFromDate:self.book.copyright]; |
break; |
} |
return cell; |
} |
// ------------------------------------------------------------------------------- |
// tableView:editingStyleForRowAtIndexPath: |
// This optional UITableViewDelegate method is overridden to disallow rows to be |
// deleted when in editing mode. |
// ------------------------------------------------------------------------------- |
- (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath |
{ |
return UITableViewCellEditingStyleNone; |
} |
// ------------------------------------------------------------------------------- |
// tableView:shouldIndentWhileEditingRowAtIndexPath: |
// This optional UITableViewDelegate method is overridden to prevent rows from |
// being indented while in editing mode. |
// ------------------------------------------------------------------------------- |
- (BOOL)tableView:(UITableView *)tableView shouldIndentWhileEditingRowAtIndexPath:(NSIndexPath *)indexPath |
{ |
return NO; |
} |
// ------------------------------------------------------------------------------- |
// prepareForSegue:sender: |
// Called when a row is selected. Configures the destination |
// EditingViewController to edit the property of book corresponding to the |
// selected row in the table view. |
// ------------------------------------------------------------------------------- |
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender |
{ |
if ([segue.identifier isEqualToString:@"EditBook"]) { |
// sender will always be a UITableViewCell |
UITableViewCell *cell = (UITableViewCell*)sender; |
// Lookup the cell's index path so we know which row was selected. |
NSIndexPath *selectedIndexPath = [self.tableView indexPathForCell:cell]; |
// Configure the destination EditingViewController. |
EditingViewController *editingController = (EditingViewController*)segue.destinationViewController; |
editingController.sourceController = self; |
editingController.editedObject = self.book; |
switch (selectedIndexPath.row) { |
case 0: // Title |
editingController.editedPropertyKey = @"title"; |
editingController.editedPropertyDisplayName = NSLocalizedString(@"title", @"display name for title"); |
editingController.editingDate = NO; |
break; |
case 1: // Author |
editingController.editedPropertyKey = @"author"; |
editingController.editedPropertyDisplayName = NSLocalizedString(@"author", @"display name for author"); |
editingController.editingDate = NO; |
break; |
case 2: // Copyright |
editingController.editedPropertyKey = @"copyright"; |
editingController.editedPropertyDisplayName = NSLocalizedString(@"copyright", @"display name for copyright"); |
editingController.editingDate = YES; |
break; |
} |
} |
} |
#pragma mark - Editing |
// ------------------------------------------------------------------------------- |
// setValue:forEditedProperty: (Declared in the PropertyEditing protocol) |
// Method to update a value in the book, and at the same time register the |
// undo/redo operation with the undo manager. |
// The implementation uses an invocation since the method requires two arguments. |
// This method is invoked by the editing view controller if the user taps Save. |
// ------------------------------------------------------------------------------- |
- (void)setValue:(id)newValue forEditedProperty:(NSString *)field |
{ |
// prepareWithInvocationTarget: pushes a new undo item onto the undo stack |
// (or onto the redop stack if this method is invoked during an undo operation). |
// If the user chooses undo, then the undo manager sends the target (self) |
// setValue:forEditedProperty: message with the arguments |
// currentValueforEditedProperty and field. |
id currentValueforEditedProperty = [self.book valueForKey:field]; |
[[self.undoManager prepareWithInvocationTarget:self] setValue:currentValueforEditedProperty forEditedProperty:field]; |
// Update the book's property to the new value. |
[self.book setValue:newValue forKey:field]; |
// Set the action name (which appears in the undo button title) to the |
// user-visible name of the field. |
if (![self.undoManager isUndoing]) |
[self.undoManager setActionName:NSLocalizedString(field, @"string provided dynamically")]; |
} |
// ------------------------------------------------------------------------------- |
// setEditing:animated |
// This method is called when the view controller should transition in or out |
// of the editing state in response to the user tapping the edit button. |
// ------------------------------------------------------------------------------- |
- (void)setEditing:(BOOL)editing animated:(BOOL)animated |
{ |
// This method is originally declared in UIViewController. We must invoke |
// its implementation. |
[super setEditing:editing animated:animated]; |
// Respond to change in editing state: |
// If editing begins, create and set an undo manager to track edits. Then |
// register as an observer of undo manager change notifications, so that if an |
// undo or redo operation is performed, the table view can be reloaded. |
// If editing ends, de-register from the notification center and remove the |
// undo manager. |
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter]; |
if (editing) { |
// Create a new undo manager. |
NSUndoManager *anUndoManager = [[NSUndoManager alloc] init]; |
self.undoManager = anUndoManager; |
// 3 levels of undo is somewhat arbitrary. It happens here to coincide |
// with the number of properties that can be edited, but in general you |
// need to consider the memory overhead of maintaining a large number of |
// undo actions, and the user interaction (how easy will it be for the user |
// to backtrack through a dozen or more actions). |
[self.undoManager setLevelsOfUndo:3]; |
// Listen for undo or redo notifications to we know when to reload the |
// table view to display the change. |
[nc addObserver:self selector:@selector(undoManagerDidUndo:) name:NSUndoManagerDidUndoChangeNotification object:self.undoManager]; |
[nc addObserver:self selector:@selector(undoManagerDidRedo:) name:NSUndoManagerDidRedoChangeNotification object:self.undoManager]; |
} |
else { |
// Tear down the undo manager. |
[nc removeObserver:self name:NSUndoManagerDidUndoChangeNotification object:self.undoManager]; |
[nc removeObserver:self name:NSUndoManagerDidRedoChangeNotification object:self.undoManager]; |
self.undoManager = nil; |
} |
} |
#pragma mark - Undo support |
// ------------------------------------------------------------------------------- |
// undoManagerDidUndo: |
// Handler for the NSUndoManagerDidUndoChangeNotification. Redisplays the table |
// view to reflect the changed value. |
// See also: -setEditing:animated: |
// ------------------------------------------------------------------------------- |
- (void)undoManagerDidUndo:(NSNotification *)notification |
{ |
[self.tableView reloadData]; |
} |
// ------------------------------------------------------------------------------- |
// undoManagerDidRedo: |
// Handler for the NSUndoManagerDidRedoChangeNotification. Redisplays the table |
// view to reflect the changed value. |
// See also: -setEditing:animated: |
// ------------------------------------------------------------------------------- |
- (void)undoManagerDidRedo:(NSNotification *)notification |
{ |
[self.tableView reloadData]; |
} |
// ------------------------------------------------------------------------------- |
// canBecomeFirstResponder |
// The view controller must be first responder in order to be able to receive |
// shake events for undo. |
// ------------------------------------------------------------------------------- |
- (BOOL)canBecomeFirstResponder |
{ |
return YES; |
} |
#pragma mark - Date formatter |
// ------------------------------------------------------------------------------- |
// dateFormatter |
// Custom implementation of the getter for the dateFormatter property. This |
// method lazily creates and configures an NSDateFormatter if one does not |
// presently exist. |
// ------------------------------------------------------------------------------- |
- (NSDateFormatter *)dateFormatter |
{ |
if (_dateFormatter == nil) { |
_dateFormatter = [[NSDateFormatter alloc] init]; |
[_dateFormatter setDateStyle:NSDateFormatterMediumStyle]; |
[_dateFormatter setTimeStyle:NSDateFormatterNoStyle]; |
} |
return _dateFormatter; |
} |
@end |
Copyright © 2013 Apple Inc. All Rights Reserved. Terms of Use | Privacy Policy | Updated: 2013-05-03