Question

这是我的代码我只得到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

问题是你在while语句的循环中实例化一个新的可变数组。您希望在循环之前实例化它一次，而在循环内部仅addObject实例化它。

NSString *sql = [NSString stringWithFormat:@"SELECT * FROM district_details"];
sqlite3_stmt *statement;

if (sqlite3_prepare_v2(db, [sql UTF8String], -1, &statement, nil)==SQLITE_OK) {
    myarray = [[NSMutableArray alloc] initWithObjects:@"--select the value--",nil];
    while (sqlite3_step(statement)==SQLITE_ROW) {
        char *field2 = (char *)sqlite3_column_text(statement, 1);
        field2Str = [[NSString alloc] initWithUTF8String:field2];
        [myarray addObject:field2Str];
    }
    sqlite3_finalize(statement);  // remember to finalize to prevent SQLite leak    
}

Answer 2

在使用它之前启动一次数组对象，如果你在循环中启动它，就像你这样做会丢失先前添加的对象并在堆内存中进行新的分配。

只需将此代码放在viewDidLoad方法中，然后从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);

如何检索sqlite列值并将其存储到目标c中的数组？

2 个答案: