1. EEC-492/693/793 iPhone Application Development
Lecture 13
Wenbing Zhao & Nigamanth Sridhar
11/15/2018
EEC492/693/793 - iPhone Application Development

2. Outline Basic Data Persistence Assignments: iPhone file system
Property list
Archiving
SQLite
Assignments:
Build the Persistence app
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EEC492/693/793 - iPhone Application Development
EEC492/693/793 - iPhone Application Development 2

3. EEC492/693/793 - iPhone Application Development
iPhone File System
Sand box mechanism
Every app gets its own home directory, and apps are only allowed to read and write from their own home directory
Normally Documents and tmp sub-directories
Better security and easier to cleanup after deleting an app
11/15/2018
EEC492/693/793 - iPhone Application Development

4. App Home Directory Layout
<Application Home>
MyApp.app
MyApp
MainWindow.nib
SomeImage.png
Documents
Library
Caches
Preferences
tmp
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EEC492/693/793 - iPhone Application Development

5. File Paths in Your Application
// Basic directories
NSString *homePath = NSHomeDirectory();
NSString *tmpPath = NSTemporaryDirectory();
// Documents directory
NSArray *paths = NSSearchPathForDirectoriesInDomains
(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0];
// <Application Home>/Documents/foo.plist
NSString *fooPath =
[documentsPath
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EEC492/693/793 - iPhone Application Development

6. Including Writable Files with Your App
Many applications want to include some starter data
But application bundles are code signed
You can’t modify the contents of your app bundle
To include a writable data file with your app...
Build it as part of your app bundle
On first launch, copy it to your Documents directory
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EEC492/693/793 - iPhone Application Development

7. EEC492/693/793 - iPhone Application Development
Property Lists
Convenient way to store a small amount of data
NSArray or NSDictionary of
NSString, NSMutableString, NSNumber, NSDate, NSData, NSMutableData
NSUserDefaults class uses property lists under the hood
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EEC492/693/793 - iPhone Application Development

8. When Not to Use Property Lists
More than a few hundred KB of data
Loading a property list is all-or-nothing
Complex object graphs
Custom object types
Multiple writers (e.g. not thread-safe)
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EEC492/693/793 - iPhone Application Development

9. Reading & Writing Property Lists
NSArray and NSDictionary convenience methods
Operate recursively
// Writing
- (BOOL)writeToFile:(NSString *)aPath atomically:(BOOL)flag;
- (BOOL)writeToURL:(NSURL *)aURL atomically:(BOOL)flag;
// Reading
- (id)initWithContentsOfFile:(NSString *)aPath;
- (id)initWithContentsOfURL:(NSURL *)aURL;
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EEC492/693/793 - iPhone Application Development

10. Writing Array & Dictionary to Disk
NSArray *array = [NSArray
[NSNumber numberWithBool:YES],
[NSDate dateWithTimeIntervalSinceNow:60],
nil];
[array atomically:YES];
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber
[dict atomically:YES];
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EEC492/693/793 - iPhone Application Development

11. EEC492/693/793 - iPhone Application Development
Archiving Objects
Next logical step from property lists
Include arbitrary classes
Complex object graphs
Used by Interface Builder for NIBs
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EEC492/693/793 - iPhone Application Development

12. Making Objects Archivable
Conform to the <NSCoding> protocol
// Encode an object for an archive
- (void)encodeWithCoder:(NSCoder *)coder {
[super encodeWithCoder:coder];
[coder encodeObject:name
[coder encodeInteger:numberOfSides }
// Decode an object from an archive
- (id)initWithCoder:(NSCoder *)coder
self = [super initWithCoder:coder];
// if subclassing NSObject directly, need to check on
// if(self = [super init]) …
name = [[coder retain];
numberOfSides = [coder
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EEC492/693/793 - iPhone Application Development

13. EEC492/693/793 - iPhone Application Development
To Enable Copying
Conform to the <NSCopying> protocol
- (id)copyWithZone:(NSZone *)zone {
MyClass *copy = [[[self class] allocWithZone:zone] init];
copy.foo = [self.foo copyWithZone:zone];
copy.bar = [self.bar copyWithZone:zone];
copy.someInt = self.someInt;
copy.someFloat = self.someFloat;
return copy; }
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EEC492/693/793 - iPhone Application Development

14. Archiving a Data Object
NSMutableData *data = [[NSMutableData alloc] init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc]
initForWritingWithMutableData:data];
[archiver encodeObject:myObject …
[archiver finishEncoding];
BOOL success = [data atomically:YES];
[archiver release];
[data release];
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EEC492/693/793 - iPhone Application Development

15. Unarchiving a Data Object
NSData *data = [[NSData alloc] initWithContentsOfFile:path];
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc]
initForReadingWithData:data];
self.object = [unarchiver …
[unarchiver finishDecoding];
[unarchiver release];
[data release];
The object returned by decodeObjectForKey: is autoreleased
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EEC492/693/793 - iPhone Application Development

16. EEC492/693/793 - iPhone Application Development
SQLite
Complete SQL database in an ordinary file
Simple, compact, fast, reliable
No server
Free/Open Source Software
Great for embedded devices
Included on the iPhone platform
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EEC492/693/793 - iPhone Application Development

17. EEC492/693/793 - iPhone Application Development
When Not to Use SQLite
Multi-gigabyte databases
High concurrency (multiple writers)
Client-server applications
“Appropriate Uses for SQLite”
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EEC492/693/793 - iPhone Application Development

18. EEC492/693/793 - iPhone Application Development
SQLite C API Basics
Open the database
int sqlite3_open(const char *filename, sqlite3 **db);
Execute a SQL statement
int sqlite3_exec(sqlite3 *db, const char *sql,
int (*callback)(void*,int,char**,char**),
void *context, char **error);
// Your callback (when query is returned)
int callback(void *context, int count,
char **values, char **columns);
Close the database
int sqlite3_close(sqlite3 *db);
Book is wrong on sqlite3_exec is used to run any command against SQLite3 that doesn’t return data (i.e., it could only be used for updates, inserts, and deletes). Actually, we can do query, you must handle the returned data in the callback (one callback per row returned)
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EEC492/693/793 - iPhone Application Development

19. Retrieving Data from SQLite3
NSString *query ID, FIELD_DATA FROM FIELDS ORDER BY ROW”;
sqlite3_stmt *statement;
int result = (sqlite3_prepare_v2( database, [query UTF8String],
-1, &statement, nil);
while (sqlite3_step(statement) == SQLITE_ROW) {
int rowNum = sqlite3_column_int(statement, 0);
char *rowData = (char *)sqlite3_column_text(statement, 1);
NSString *fieldValue = [[NSString alloc] initWithUTF8String:rowData];
// Do something with the data here
[fieldValue release]; }
sqlite3_finalize(statement);
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EEC492/693/793 - iPhone Application Development

20. EEC492/693/793 - iPhone Application Development
Bind Variables
Used when inserting into a database
Making sure strings don’t have invalid characters, etc.
char *sql = “insert into foo values (?, ?);”;
sqlite3_stmt *stmt;
if (sqlite3_prepare_v2(database, sql, -1, &stmt, nil) == SQLITE_OK) {
sqlite3_bind_int(stmt, 1, 235);
sqlite3_bind_text(stmt, 2, “Bar”, -1, NULL); }
if (sqlite3_step(stmt) != SQLITE_DONE)
should be real error checking!”);
sqlite3_finalize(stmt);
Sqlite3_bind_text, beyond the first 3 parameters:
The first is the length of the data being passed in the third parameter. In the case of C strings, you can pass
-1 instead of the string’s length, and the function will use the entire string. In all other cases,
you have to tell it the length of the data being passed int.
The final parameter is an optional
function callback in case you need to do any memory cleanup after the statement is executed
11/15/2018
EEC492/693/793 - iPhone Application Development