使用CoreData [1]

最新推荐文章于 2021-10-26 22:17:14 发布

转载最新推荐文章于 2021-10-26 22:17:14 发布 · 86 阅读

本文提供了一个CoreData的入门教程，详细介绍了如何从无开始接触CoreData，包括创建工程、实体、对象操作等基本步骤。通过实践示例，展示了存储、查询、删除和修改对象的方法。

使用CoreData [1]

本篇教程能教你从无开始接触CoreData,包括新建工程,创建出实体,增删改查样样都有,属于使用CoreData最初级教程.

1. 创建带有CoreData的工程项目

2. 添加一个实体类

3. 创建出实体类

4. 创建对象,保存对象,执行代码

以下是验证结果:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    NSLog(@"%@", NSHomeDirectory());
    
    // 实体描述信息
    NSEntityDescription *description = \
        [NSEntityDescription entityForName:@"Student"
                    inManagedObjectContext:[self managedObjectContext]];
    
    // 初始化对象
    Student *student = [[Student alloc] initWithEntity:description
                        insertIntoManagedObjectContext:[self managedObjectContext]];
    student.name     = @"YouXianMing";
    student.age      = [NSNumber numberWithInt:26];
    
    // 保存对象
    [self saveContext];

    return YES;
}

这样就实现了存储对象.

5. 重复上面的步骤存储5个对象.

6. 遍历出所有的对象

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // 设定要查询的实体
    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];
    
    // 取出查询结果
    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];
    
    // 遍历
    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        Student *student = obj;
        NSLog(@"%@ %@", student.age, student.name);
    }];

    return YES;
}

7. 删除一个对象

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // 设定要查询的实体
    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];
    
    // 取出查询结果
    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];
    
    // 遍历
    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        Student *student = obj;

        // 找到匹配的数据,删除之
        if ([student.name isEqualToString:@"QiuLiang"])
        {
            [[self managedObjectContext] deleteObject:student];
        }
    }];
    
    // 存储
    [self saveContext];
    
    // 遍历
    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        Student *student = obj;
        
        NSLog(@"%@ %@", student.age, student.name);
    }];

    return YES;
}

8. 修改一个对象

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // 设定要查询的实体
    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];
    
    // 取出查询结果
    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];
    
    // 遍历
    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        Student *student = obj;

        // 找到匹配的数据,修改之
        if ([student.name isEqualToString:@"YouXianMing"])
        {
            student.age = [NSNumber numberWithInt:100];
        }
    }];
    
    // 存储
    [self saveContext];
    
    // 遍历
    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        Student *student = obj;
        
        NSLog(@"%@ %@", student.age, student.name);
    }];

    return YES;
}