UIImage对象意外返回null，但未返回NSData

Question

i have created a sqlite db.

and i have insert a few datas in my db..

UIImage * imagee=[UIImage imageNamed:@"image.png"];
NSData *mydata=[NSData dataWithData:UIImagePNGRepresentation(imagee)];
const char *dbpath = [databasePath UTF8String];

NSString *insertSQL=[NSString stringWithFormat:@"insert into CONTACTS values(\"%@\",\"%@\")",@"Mathan",mydata];

NSLog(@"mydata %@",mydata);

sqlite3_stmt *addStatement;

const char *insert_stmt=[insertSQL UTF8String];
if (sqlite3_open(dbpath,&contactDB)==SQLITE_OK) {
    sqlite3_prepare_v2(contactDB,insert_stmt,-1,&addStatement,NULL);

    if (sqlite3_step(addStatement)==SQLITE_DONE) {

        sqlite3_bind_blob(addStatement,1, [mydata bytes], [mydata length], SQLITE_TRANSIENT);
        NSLog(@"Data saved");

    }
    else{

        NSLog(@"Some Error occured");
    }

    sqlite3_close(contactDB);
}
else{
    NSLog(@"Failure");
}

have written some codes to retrive the data

sqlite3_stmt *statement;
if (sqlite3_open([databasePath UTF8String], &contactDB) == SQLITE_OK) {
    NSString *sql = [NSString stringWithFormat:@"SELECT * FROM contacts"];

    if (sqlite3_prepare_v2( contactDB, [sql UTF8String], -1, &statement, nil) == SQLITE_OK) {
        while (sqlite3_step(statement) == SQLITE_ROW)
        {
            char *field1 = (char *) sqlite3_column_text(statement, 0);
            NSString *field1Str = [[NSString alloc] initWithUTF8String: field1];
            NSLog(@"UserName %@",field1Str);

            NSData *data = [[NSData alloc] initWithBytes:sqlite3_column_blob(statement, 1) length:sqlite3_column_bytes(statement, 1)];

            UIImage *newImage = [[UIImage alloc]initWithData:data];

            NSLog(@"Image OBJ %@",newImage);
            NSLog(@"Image Data  %@",data);
        }
        sqlite3_close(contactDB);
    }
}

sqlite3_finalize(statement);

the problem is

in log, inserted NSData object and retrieved NSData objects are different (printing in log gives different stream)

moreover Image OBJ is printed null in log..

Have seen similar questions in stackoverflow. But nothing seems to help.

Answer 1

When you do this:

NSData *data = [[NSData alloc] initWithBytes:sqlite3_column_blob(statement, 1) length:sqlite3_column_bytes(statement, 1)];
UIImage *newImage = [[UIImage alloc]initWithData:data];

You are telling the compiler that the two objects are different, so when you print them, they will always be different. Guaranteed. Since they aren't the same object.

I'm not sure why newImage would display null though since you just allocated the object.

Answer 2

You should perform sqlite3_step after sqlite3_bind_blob , not before. You're inserting before you tell it what to insert!

Checking results of sqlite_prepare_v2 and sqlite3_bind_blob would be prudent, too.

I'd also suggest (unrelated to your question) sqlite3_finalize before you sqlite3_close in both snippets of code. And if you have an error, sqlite3_errmsg is a life saver, telling you precisely what went wrong, rather than guessing.

Answer 3

There is not a major difference but you can try with this and also you can get the image length in console to detect image is properly responding from database or not:

const void *ptr = sqlite3_column_blob(stmt, 1);
int size = sqlite3_column_bytes(stmt, 1);
NSLog(@"%d",size);
data = [[NSData alloc] initWithBytes:ptr length:size];