What's causing this?

I don't understand "why" SQLiteDB may not respond to "-checkIfDatabaseExists". What's causing this and how do I fix it? (I'm real close to getting this to work, but because I'm a newbie, I am still having problems).

I appreciate any assistance I can get on this. Here is the code:

#import "SQLiteDB.h"

static SQLiteDB *sharedSQLiteDB = nil;  //  makes this a singleton class

@implementation SQLiteDB

@synthesize db, dbPath, databaseKey;


//--------------    check for database or create it    ----------------|
#pragma mark Singleton Methods

+ (SQLiteDB *) sharedSQLiteDB  {

    if(!sharedSQLiteDB)  {
        sharedSQLiteDB = [[SQLiteDB alloc] init];
        [sharedSQLiteDB checkIfDatabaseExists开发者_运维百科];
    }
    return sharedSQLiteDB;
}   

+(id)allocWithZone:(NSZone *)zone  {
    if(!sharedSQLiteDB)  {
        sharedSQLiteDB = [super allocWithZone:zone];
        return  sharedSQLiteDB;
    }
    else {
        return nil;
    }
}   

-(id)copyWithZone:(NSZone *)zone  {
    return self;
}

-(void) release  {
    //  no-op
}


- (void) checkIfDatabaseExists  {
    // Get the path to the database file
    NSArray *searchPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentPath = [searchPaths objectAtIndex:0];
    NSString *databasePath = [documentPath stringByAppendingPathComponent:@"ppcipher.s3db"];

    // Open the database file
    const char *cDatabasePath = [databasePath cStringUsingEncoding:NSUTF8StringEncoding];
    if(sqlite3_open(cDatabasePath, &db) == SQLITE_OK)  //  does it exist?
        return;
    else {  //  create database file here

    }

}
@end

---

I'm not 100% sure about what you've implemented here, but from what I can tell, your header has defined +checkIfDatabaseExists as a class method (although you haven't implemented it yet, hence the "incomplete implementation" and "method definition not found" warnings). However, in your sharedSQLiteDB method, you are calling -checkIfDatabaseExists on an instance of SQLiteDB which refers to a instance method that you have not defined.

Edit: Okay, after seeing the full code, my above answer is obviously not the case. But what does your header look like? Do you have a + instead of a - in front of the checkIfDatabaseExists signature?

---

When you have:

- (void) foo
{
   [self bar];
}

- (void) bar
{ ... }

The compiler hasn't seen the definition of -bar when compiling -foo and, thus, will warn that self may not respond to -bar when compiling -foo.

If that method is intended to be entirely private to the class, then do this at the top of the .m file:

@interface Foo()
- (void) bar;
@end

If it is intended to be called by other classes, add the method declaration to the @interface.