ios - 数据库类的使用及其在 Objective C iOS 中的方法

Question

我正在尝试在 iOS 中使用数据库 SQLite。我在下面的代码中有几个问题。

#import "DBManager.h"

static DBManager *sharedInstance = nil;
static sqlite3 *database = nil;
static sqlite3_stmt *statement = nil;


@implementation DBManager

+(DBManager*)getSharedInstance{
    if (!sharedInstance) {
        sharedInstance = [[     super allocWithZone:NULL]init];
        [sharedInstance createDB];
    }
    return sharedInstance;
}

-(BOOL)createDB{
    NSString *docsDir;
    NSArray *dirPaths;
    // Get the documents directory
    dirPaths = NSSearchPathForDirectoriesInDomains
    (NSDocumentDirectory, NSUserDomainMask, YES);
    docsDir = dirPaths[0];
    // Build the path to the database file
    databasePath = [[NSString alloc] initWithString:
                    [docsDir stringByAppendingPathComponent: @"calc.db"]];
    BOOL isSuccess = YES;
    NSFileManager *filemgr = [NSFileManager defaultManager];
    if ([filemgr fileExistsAtPath: databasePath ] == NO)
    {
        const char *dbpath = [databasePath UTF8String];
        if (sqlite3_open(dbpath, &database) == SQLITE_OK)
        {
            char *errMsg;
            const char *sql_stmt =
            "create table if not exists resultDetail (results integer)";
            if (sqlite3_exec(database, sql_stmt, NULL, NULL, &errMsg)
                != SQLITE_OK)
            {
                isSuccess = NO;
                NSLog(@"Failed to create table");
            }
            sqlite3_close(database);
            return  isSuccess;
        }
        else {
            isSuccess = NO;
            NSLog(@"Failed to open/create database");
        }
    }
    return isSuccess;
}


- (BOOL) saveData:(int)resultValue ;
{
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *insertSQL = [NSString stringWithFormat:@"insert into resultDetail (results) values (\"%d\")",resultValue];
        const char *insert_stmt = [insertSQL UTF8String];
        sqlite3_prepare_v2(database, insert_stmt,-1, &statement, NULL);
            if (sqlite3_step(statement) == SQLITE_DONE)
            {
                sqlite3_reset(statement);
                return YES;
            }
            else
            {
                return NO;
            }
         //   sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return NO;
}


- (int) findResult:(int)resultValue
{
    int n=0;
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *querySQL = [NSString stringWithFormat:@"select results from resultDetail where results=\"%d\"",resultValue];

   //     NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];
        const char *query_stmt = [querySQL UTF8String];
    //    NSMutableArray *resultArray = [[NSMutableArray alloc]init];
        if (sqlite3_prepare_v2(database,
                               query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {
         /*  if (sqlite3_step(statement) == SQLITE_ROW)
            {
                int n = sqlite3_column_int(statement, 0);
                NSLog(@"%d let's see",n);
                sqlite3_reset(statement);
                return n;
            }
            else{
                NSLog(@"Not found");
                return 0;
            }    */
           while(sqlite3_step(statement) == SQLITE_ROW){
                n = sqlite3_column_int(statement, 0);
                NSLog(@"%d is the value",n);

            }
            return n;
         //   sqlite3_reset(statement);
        }
        sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return 0;
}

-(BOOL)isEmpty{
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];

        //     NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];
        const char *query_stmt = [querySQL UTF8String];
        //    NSMutableArray *resultArray = [[NSMutableArray alloc]init];
        if (sqlite3_prepare_v2(database,
                               query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {

            if(sqlite3_step(statement) == SQLITE_ROW){
               sqlite3_reset(statement);
                NSLog(@"Not Empty");
                return NO;
            }
        }
        sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return YES;
}

-(BOOL)isDuplicate:(int)resultValue{
    BOOL n=NO;
    const char *dbpath = [databasePath UTF8String];
    if (sqlite3_open(dbpath, &database) == SQLITE_OK)
    {
        NSString *querySQL = [NSString stringWithFormat:@"select results from resultDetail where results=\"%d\"",resultValue];

        //     NSString *querySQL = [NSString stringWithFormat:@"select * from resultDetail"];
        const char *query_stmt = [querySQL UTF8String];
        //    NSMutableArray *resultArray = [[NSMutableArray alloc]init];
        if (sqlite3_prepare_v2(database,
                               query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {
            if(sqlite3_step(statement) == SQLITE_ROW){
                sqlite3_reset(statement);
                n = YES;
            }
            sqlite3_reset(statement);
            return n;
            //   sqlite3_reset(statement);
        }
        sqlite3_reset(statement);
    }
    sqlite3_reset(statement);
    return NO;
}
@end

---

在上面的代码中，这是什么

static sqlite3 *database = nil;
static sqlite3_stmt *statement = nil;

这是类还是方法？

---

我们为什么要创建 getSharedInstance 以及它的用途是什么？

+(DBManager*)getSharedInstance{
    if (!sharedInstance) {
        sharedInstance = [[     super allocWithZone:NULL]init];
        [sharedInstance createDB];
    }
    return sharedInstance;
}

---

这里的 NULL 参数是什么，我们实际上要如何处理它们？

sqlite3_exec(database, sql_stmt, NULL, NULL, &errMsg)
                != SQLITE_OK

---

我是ios新手，所以如果我问的有什么问题请纠正我。感谢您抽出时间(:

Answer 1

答案太长，所以请阅读本教程，您可以了解 SQLite 如何在 iOS 中工作

http://www.appcoda.com/sqlite-database-ios-app-tutorial/