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我有带有核心数据的 iOS 应用程序，在我的一个功能中，我加载信息以通过这种方式显示我的应用程序的一个视图：

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription 
                               entityForName:@"MyDate" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];

NSError *error;

NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:fetchRequest error:&error];

for (NSManagedObject *info in fetchedObjects) {

    if ([[[info valueForKey:@"status"] description] isEqualToString:@"Done"]) {

        NSArray *allTask = [[info valueForKey:@"taskes"] allObjects];
        for (NSManagedObject *task in allTask) {
            NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
            [dateFormatter setDateFormat:@"yyyy-MM-dd"];

            if (IsDateBetweenInclusive([task valueForKey:@"firstDate"], fromDate, toDate)) {

                [taskArray addObject:task];
            }
        }
    }
}

所以我迭代所有数据库以查找信息然后显示它，当我的数据库中的信息很少时，上面的方法很快，但是当我的数据库中的信息更多时，在我的 3GS 上需要几秒钟来显示该视图，而不是模拟器中的速度很快，所以我的问题是，有一种快速的方法可以从核心日期获取信息吗？我不知道有一个快速调用属性和我想从核心数据中检索的值？

谢谢

4

2 回答 2

2

使用 NSPredicate，见https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html

以下代码将仅获取状态字段设置为“完成”的值

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"MyDate" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"status == 'Done'"]];

NSError *error;

NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
于 2012-04-17T13:33:36.557 回答
0

创建database：

NSString *docsDir; NSArray *dirPaths;

dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

docsDir = [dirPaths objectAtIndex:0];
databasePath = [[NSString alloc] initWithString: [docsDir stringByAppendingPathComponent: @"newapp.sqlite"]];

NSFileManager *filemgr = [NSFileManager defaultManager];

if ([filemgr fileExistsAtPath: databasePath ] == NO)
{
    const char *dbpath = [databasePath UTF8String];

    if (sqlite3_open(dbpath, &contactDB) == SQLITE_OK)
    {
        char *errMsg;
        const char *sql_stmt = "CREATE TABLE IF NOT EXISTS LIST (id VARCHAR, title VARCHAR , description VARCHAR ,date VARCHAR)";


        if ((sqlite3_exec(contactDB, sql_stmt, NULL, NULL, &errMsg) != SQLITE_OK) )
        {
            UIAlertView *alert=[[UIAlertView alloc]initWithTitle:@"Warning" message:@"Failed to create table" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alert show];
                        }

        sqlite3_close(contactDB);

    } else {
        UIAlertView *alert=[[UIAlertView alloc]initWithTitle:@"Warning" message:@"Failed to open/create database" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];

    }
}

插入值

NSString *id_str=@"21"; NSString *title=@"notisa"; NSString *description=@"新应用"; NSString *date=@"21/4/30";

const char *dbpath = [databasePath UTF8String];

if (sqlite3_open(dbpath, &contactDB) == SQLITE_OK){
    // error handling...
}
// Construct the query and empty prepared statement.
const char *sql = "INSERT INTO `LIST` (`id`,`title`,`description`,`date`) VALUES (?, ?, ?, ?)";
sqlite3_stmt *statement;

   // UIImage *image = [UIImage imageWithData:imgdata];
//NSData *imageData=UIImagePNGRepresentation(image);

// Prepare the statement.
if (sqlite3_prepare_v2(contactDB, sql, -1, &statement, NULL) == SQLITE_OK) {
    // Bind the parameters (note that these use a 1-based index, not 0).


    sqlite3_bind_text(statement,1, [id_str UTF8String], -1, SQLITE_TRANSIENT);
    sqlite3_bind_text(statement,2, [title UTF8String], -1, SQLITE_TRANSIENT);
    sqlite3_bind_text(statement,3, [description UTF8String], -1, SQLITE_TRANSIENT);
    sqlite3_bind_text(statement,4, [date UTF8String], -1, SQLITE_TRANSIENT);

        }

// Execute the statement.
if (sqlite3_step(statement) != SQLITE_DONE) {
    // error handling...
    UIAlertView *alert=[[UIAlertView alloc]initWithTitle:@"Warning" message:@"Failed to Save" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
       }
else
{
    UIAlertView *alert=[[UIAlertView alloc]initWithTitle:@"Database" message:@"Stored Successfully" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
     }
// Clean up and delete the resources used by the prepared statement.
sqlite3_finalize(statement);
sqlite3_close(contactDB);

选择数据库： const char *dbpath = [databasePath UTF8String]; sqlite3_stmt *语句；

if (sqlite3_open(dbpath, &contactDB) == SQLITE_OK)
{
    NSString *querySQL = [NSString stringWithFormat: @"SELECT id,title,description,date FROM LIST"];

    const char *query_stmt = [querySQL UTF8String];

    if (sqlite3_prepare_v2(contactDB, query_stmt, -1, &statement, NULL) == SQLITE_OK)
    {
        while(sqlite3_step(statement) == SQLITE_ROW)
        {
            NSLog(@"ROW-->%d",SQLITE_ROW);

            const char* policyNo  = (const char *)sqlite3_column_text(statement, 1);
            NSString *PolicyNumber = policyNo == NULL ? nil : [[NSString alloc]initWithUTF8String:policyNo];


            NSLog(@"PolicyNumber:%@",PolicyNumber);

            const char* start  = (const char *)sqlite3_column_text(statement, 2);
            NSString *startDate = start == NULL ? nil : [[NSString alloc]initWithUTF8String:start];

            const char* end  = (const char *)sqlite3_column_text(statement, 3);
            NSString *endDate = end == NULL ? nil : [[NSString alloc]initWithUTF8String:end];


                   }
        sqlite3_finalize(statement);
    }
    sqlite3_close(contactDB);
}

删除 ：

const char *dbpath = [databasePath UTF8String]; sqlite3_stmt *语句；

if (sqlite3_open(dbpath, &contactDB) == SQLITE_OK)
{
    NSString *querySQL = [NSString stringWithFormat: @"DELETE id,title,description,date FROM LIST"];

    const char *query_stmt = [querySQL UTF8String];

    if (sqlite3_prepare_v2(contactDB, query_stmt, -1, &statement, NULL) == SQLITE_OK)
    {
        while(sqlite3_step(statement) == SQLITE_ROW)
        {
            NSLog(@"ROW-->%d",SQLITE_ROW);

            const char* policyNo  = (const char *)sqlite3_column_text(statement, 1);
            NSString *PolicyNumber = policyNo == NULL ? nil : [[NSString alloc]initWithUTF8String:policyNo];


            NSLog(@"PolicyNumber:%@",PolicyNumber);

            const char* start  = (const char *)sqlite3_column_text(statement, 2);
            NSString *startDate = start == NULL ? nil : [[NSString alloc]initWithUTF8String:start];

            const char* end  = (const char *)sqlite3_column_text(statement, 3);
            NSString *endDate = end == NULL ? nil : [[NSString alloc]initWithUTF8String:end];


        }
        sqlite3_finalize(statement);
    }
    sqlite3_close(contactDB);
}
于 2013-10-24T06:41:54.043 回答