objective-c - 如何使 FMDB 的数据库成为单例

Question

我已经使用 SQLite 一段时间了，并决定去 FMDB。我需要使它成为一个单例。下面是我的代码；为了让 FMDB 访问单例 d/b，我需要进行哪些更改？

#pragma mark Singleton Methods

+ (SQLiteDB *) sharedSQLiteDB  {

    if(!sharedSQLiteDB)  {
        sharedSQLiteDB = [[SQLiteDB alloc] init];
        [sharedSQLiteDB openCreateDB];  //  check to see if d/b exists
    }
    return sharedSQLiteDB;
}   

这是我使用 FMDB 初始化 d/b 的代码：

//-----------------------    checkIfDatabaseExists    -----------------|
    - (void) openCreateDB  {

        searchPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);  // Get the path to the database file
        documentPath = [searchPaths objectAtIndex:0];
        databasePath = [documentPath stringByAppendingPathComponent:@"ppcipher.s3db"];
        cDatabasePath = [databasePath cStringUsingEncoding:NSUTF8StringEncoding];
        NSLog(@"d/b path: /%@", databasePath);

        NSString *sqlCommand = @"CREATE TABLE CardData (card_id TEXT PRIMARY KEY NOT NULL, card_name TEXT NOT NULL, "
            @"card_type TEXT, code_val TEXT, create_date TEXT DEFAULT CURRENT_DATE, user_notes TEXT, gps_loc TEXT)"; 
        char * errmsg = nil;   

        NSFileManager *fileManager = [NSFileManager defaultManager];
        [fileManager removeItemAtPath:databasePath error:NULL];  //  <------------  delete d/b  TESTING ONLY! 

        BOOL fileExists = [fileManager fileExistsAtPath:databasePath];
        if(!fileExists)  {
            FMDatabase* db = [FMDatabase databaseWithPath: databasePath]; 

            if (![db open]) {
                NSLog(@"Could not open/create database");
            }

            [db executeUpdate:@"CREATE TABLE CardData (card_id TEXT PRIMARY KEY NOT NULL, card_name TEXT NOT NULL, "
             @"card_type TEXT, code_val TEXT, create_date TEXT DEFAULT CURRENT_DATE, user_notes TEXT, gps_loc TEXT)"];

            if(errmsg != nil)
                NSLog(@"error: %s", errmsg);  //  DEBUGGING ONLY!  (REMOVE when done!)
        }
        return;
    }

Answer 1

您的 SQLiteDB 类将需要维护对 FMDatabase 的引用，以便您的其他方法能够共享同一个数据库。

@interface SQLiteDB : NSObject //Or whatever base class
{
    FMDatabase *_database;
}

@end

//implementation

- (void) openCreateDB  {
   ...
   if(!fileExists)  {
      _database = [[FMDatabase databaseWithPath: databasePath] retain];
   ...
   }
}