如果没有返回行，iPhone SQLite 查询会崩溃

Question

我的 iPhone 项目中有以下功能，效果很好......除非查询返回任何内容，然后应用程序崩溃。在没有任何断点被激活的情况下进行调试是一件痛苦的事情!

我知道这是有效的，因为我传入数据库中的静态内容并返回一个值。

-(NSString *)getSomeText:(NSString *)toPass {
    sqlite3 *database;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:@"sf.sqlite"];

    int strLength = 0;
    strLength = [toPass length];

    if (strLength <3)
        return @"Unknown";


    NSString *MIDstr;
    NSMutableString * toPass Copy = [NSMutableString stringWithString:toPass];
    MIDstr = [toPassCopy substringWithRange:NSMakeRange(0, 3)];


    // Open the database from the users filessytem
    if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {
        // Setup the SQL Statement and compile it for faster access
        NSString *BaseSQL = [NSString stringWithFormat:@"select * from MIDS where MID = '%@'",MIDstr];
        NSLog(BaseSQL);

        const char *sqlStatement = [BaseSQL UTF8String];
        //NSLog(BaseSQL);
        sqlite3_stmt *compiledStatement;
        if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
            // Loop through the results and add them to the feeds array

            while(sqlite3_step(compiledStatement) == SQLITE_ROW) {


                    NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];
                    NSString *returnString = [NSString stringWithFormat:@"%@",aName];
                    return returnString;                

            }
        }
        // Release the compiled statement from memory
        sqlite3_finalize(compiledStatement);

    }
    sqlite3_close(database);

}

Answer 1

A.如果 sqlite3_step 不返回任何行，则会崩溃，因为您已声明要返回 NSString，但是当没有行时，您不会返回任何内容。 调用者将尝试从堆栈中读取 NSString，从而最终取消引用垃圾。

要快速解决问题，请编写:

    sqlite3_close(database);
    return nil;
}

并确保调用者处理nil结果。

B/如果您确实有数据，您的代码永远不会调用sqlite3_finalize和sqlite3_close，因为您提前返回:

while(sqlite3_step(compiledStatement) == SQLITE_ROW) {
    [..]
    return returnString;