objective-c - 如何检索sqlite列值并将其存储到 objective-c 中的数组中？

Question

这是我的代码，我只获取数组中数据库的最后一个值，但我需要数组中的整个列值...

//select the values from the db
NSString *sql = [NSString stringWithFormat:@"SELECT * FROM district_details"];
sqlite3_stmt *statement;

if (sqlite3_prepare_v2(db, [sql UTF8String], -1, &statement, nil)==SQLITE_OK)
{
    while (sqlite3_step(statement)==SQLITE_ROW)
    {
        char *field2 = (char *)sqlite3_column_text(statement, 1);
        field2Str = [[NSString alloc]initWithUTF8String:field2];
        str = [NSString stringWithFormat:@"%@", field2Str];           NSLog(@"the value from thr field1 from the district name is %@...",field2Str);
        myarray =[[NSMutableArray alloc]initWithObjects:@"--select the value--",nil];
        [myarray addObject:field2Str];
        NSLog(@"the value of the myarray is......%@",myarray);
    }

}

Answer 1

在使用数组对象之前，先初始化一次数组对象，如果像在do那样在while循环内部初始化它，它将丢失先前添加的对象，并在堆内存中进行新分配。

只需将这段代码放入viewDidLoad方法中并从while循环中删除：

- (void)viewDidLoad {
    [super viewDidLoad];
    // mutable array allocation do once here  
    myarray =[[NSMutableArray alloc]initWithObjects:@"--select the value--",nil];
}

现在使用下面的代码从数据库中获取整个列：

//select the values from the db
NSString *sql = [NSString stringWithFormat:@"SELECT * FROM district_details"];
sqlite3_stmt *statement;

if (sqlite3_prepare_v2(db, [sql UTF8String], -1, &statement, nil)==SQLITE_OK)
{
    while (sqlite3_step(statement)==SQLITE_ROW)
    {
        char *field2 = (char *)sqlite3_column_text(statement, 1);
        field2Str = [[NSString alloc]initWithUTF8String:field2];

        // --------- myarray allocation removed from here -----------

        [myarray addObject:field2Str];
        NSLog(@"the value of the myarray is......%@",myarray);
    }
    sqlite3_finalize(statement);
}
sqlite3_close(db);