iOS Fundamentals Part 2

Scene & Segues

• Use blocks for communication between scenes (save or cancel)
• typedef returntype(^<#block name#>)(<#arguments#>);
• block properties should always be copy
• Two common styles:
  1. Show: left-to-right navigation
  2. Present Modally: full-screen cover
• Use prepareForSegue: to connect
  • Set the completion handler: insert new quote into models; have table view reload data; dismiss view controller

Data Persistence

1. User Default: NSUserDefaults using key value (like NSDictionary)
2. Save files to the Document folder using plist
3. Use SQLite
4. Use Core Data

Folder to save

• Documents
  • Your application stores its data in Documents, with the exception of NSUserDefaults-based preference settings
• Library
  • NSUserDefaults-based preference settings are stored in the Library/Preferences folder
• tmp
  • Place to store temporary files that will not be backed up by iTunes, but your app has to be responsibility for deleting the files

User Defaults

• No high performance
• No complex structure
• Not searchable

NSString *const kCurrentIndexKey = @"CurrentIndex";
- (void) save{
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:[NSNumber numberWithInt:self.currentIndex] forKey:kCurrentIndexKey];
    [defaults synchronize];
}  

- (NSNumber) read {
  NSNumber *readData = [[NSUserDefaults standardUserDefaults] objectForKey:kCurrentIndexKey];
  return readData;
}

Use of const

1. Prevent mistype
2. Convenience to auto-complete
3. Declare outside of @interface and @implementation

Inside Document Folder

• Accept types:
  • Property List (xml)
  • Text Files
  • Archiving Objects – NSCoding protocol

 NSString *documentsDirPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
 // Create a file name for your file
 NSString *filename = @"flashcards.plist";
 // Generate the full file path
 _filePath = [NSString stringWithFormat:@"%@/%@", documentsDirPath, filename];

 NSLog(@"file path %@", _filePath);

 NSArray *flashcardsFromDocumentsDir = [[NSArray alloc] initWithContentsOfFile:_filePath];

App life cycle

App States

• Not Running
• Inactive (foreground)
• Active (foreground)
• Background
• Suspended

Memory

Two Methods of application memory management

1. Manual retain-release: MRR
2. Automatic Reference Counting: ARC

• Using reference-count
• Invoke dealloc automatically

MRR

Cocoa’s Policy

• You own object you created: alloc new copy mutableCopy
• Take ownership by using retain
• When no longer need, relinquish it using release or autorelease (must relinquish object do not own)
• “Parent” object maintain strong reference to “children”, “children” have weak reference to “parents”

Pratical Memory Management

• Use accessor methods to set property values
• Don’t use accessor methods in initalizer and dealloc
• Use weak reference to avoid retain cycles
• Avoid dealloc object while using
• Don’t use dealloc to manage scarce resources
• Collections own the objects they contain
• Ownership policy is implemented using retain counts

Retain Count

• When create an object, RC (retain count) is 1
• When send a retain message, RC + 1
• When send a release message, RC - 1
• When you send an object a autorelease message, its retain count is decremented by 1 at the end of the current autorelease pool block.
• If RC == 0 -> object dealloc

ARC

Insert retains and releases into code when compile

Web View

WebKit

• Follow MVC framework
  • View: WebView
  • Object: WebFrameView and WebFrame
• App Transport Security force to connect with web service through HTTPS

Example:

Read a pdf file

- (void)viewDidLoad {
[super viewDidLoad];
NSString *path = [[NSBundle mainBundle] pathForResource:@"HIG" ofType:@"pdf"];
if (path){
NSData *pdfData = [NSData dataWithContentsOfFile:path];
[(UIWebView *)self.view loadData:pdfData MIMEType:@"application/pdf"
textEncodingName:@"utf-8" baseURL:nil];
}
}

Read a url

NSURL *url = [NSURL URLWithString:@"https://www.apple.com"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[self.myWebView loadRequest: request];

Cancel a loading request

- (void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
if ([self.myWebView isLoading]){
[self.myWebView stopLoading];
}
// Disconnect the delegate as the webview is hidden
self.myWebView.delegate = nil;
}

Animation loading in WebView

- (void)webViewDidStartLoad:(UIWebView *)webView{
[self.activityIndicator startAnimating];
}
- (void)webViewDidFinishLoad:(UIWebView *)webView{
[self.activityIndicator stopAnimating];
}
- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error{
[self.activityIndicator stopAnimating];
}

Notes

1. A web view automatically converts telephone numbers that appear in web content to Phone links.
2. You should not embed UIWebView or UITableView objects in UIScrollView objects.

Table View Rewind

Modifying Tables

Delete table cells

• Add navigation control
• Enable edit button in viewDidLoad method
• Use the public remove method in the model
• Implement tableView: commitEditingStyle: forRowAtIndexPath method

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source
        [self.model removeFlashcardAtIndex:indexPath.row];
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
    } else if (editingStyle == UITableViewCellEditingStyleInsert) {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
    }   
}