[__NSCFString objectForKey:]: unrecognized selector sent to instance 0xa6a2750 - ios

Question

I converted my database value to JSON format. It's showing in URL as JSON. Then i'm fetching value from JSON URL then store to local database. But i'm getting below error: [__NSCFString objectForKey:]: unrecognized selector sent to instance 0xa6a2750 and *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString objectForKey:]: unrecognized selector sent to instance 0xa6a2750'
JSON value in URL:
[{"cat_id":"196","category_name":"Performance Parts"},{"cat_id":"212","category_name":"Car Care"}]
Getting value and insert to local:
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:#"Mdb.sqlite"];
NSLog(#"filepath %#",path);
//NSDictionary *jsonDict = [stringFromFileAtURL JSONValue];
//array
NSArray *userData = [str JSONValue];
// NSLog(#"userData is %#", userData);
BOOL notExist = TRUE;
sqlite3_stmt *statement, *addStmt;
for (NSArray *skarray in userData) {
NSLog(#"test");
for (NSDictionary *tuser in skarray) {
NSLog(#"test1");
//write all this in the table
//if already exists in data base id then overwrite the name
//category table
//NSLog(#"CategoryId is %#",[tuser objectForKey:#"cat_id"]);
//NSLog(#"CategoryName is %#",[tuser objectForKey:#"cat_name"]);
if (sqlite3_open([path UTF8String], &database) == SQLITE_OK) {
NSLog(#"test2");
const char *sql = [[NSString stringWithFormat:#"SELECT cat_id FROM categories where cat_id = '%#'",[tuser objectForKey:#"cat_id"]] cStringUsingEncoding:NSUTF8StringEncoding];
NSLog(#"test3");
NSLog(#"check category is %s", sql);
if (sqlite3_prepare_v2(database, sql, -1, &statement, NULL) == SQLITE_OK) {
notExist = TRUE;
while (sqlite3_step(statement) == SQLITE_ROW) {
notExist = FALSE;
}
}
if(notExist){
//NSLog(#"cat id does not exist");
const char *sqlInsert = [[NSString stringWithFormat:#"insert into categories (cat_id, category_name) values ('%#', '%#')", [tuser objectForKey:#"cat_id"], [tuser objectForKey:#"category_name"]] cStringUsingEncoding:NSUTF8StringEncoding];
NSLog(#"Insert category is %s", sqlInsert);
if(sqlite3_prepare_v2(database, sqlInsert, -1, &addStmt, NULL) != SQLITE_OK)
NSAssert1(0, #"Error while creating add statement. '%s'", sqlite3_errmsg(database));
if(SQLITE_DONE != sqlite3_step(addStmt))
NSAssert1(0, #"Error while inserting data. '%s'", sqlite3_errmsg(database));
}
}
}
}

Answer 1

Remove for (NSArray *skarray in userData) { loop and use
for (NSDictionary *tuser in userData) {
NSLog(#"test1");
if (sqlite3_open([path UTF8String], &database) == SQLITE_OK) {
const char *sql = [[NSString stringWithFormat:#"SELECT cat_id FROM categories where cat_id = '%#'",[tuser objectForKey:#"cat_id"]] cStringUsingEncoding:NSUTF8StringEncoding];
if (sqlite3_prepare_v2(database, sql, -1, &statement, NULL) == SQLITE_OK) {
notExist = TRUE;
while (sqlite3_step(statement) == SQLITE_ROW) {
notExist = FALSE;
}
}

Answer 2

You're trying to get data from NSDictionary (or mutable) but in your case, somehow it converts to NSString (NSCFString) and which don't have objectForKey property. Take a look into steps you're compiling where you using objectForKey.