ios - 不确定为什么 NSUserdefaults 不保存结果？

Question

我正在尝试将选中的表格单元格保存并删除未选中的表格单元格到 NSUserdefaults 中，但它似乎忽略了它，因为 for 循环中的 NSLog 永远不会被调用不知道为什么，这段代码有问题吗？ (一切都显示正确，单元格得到正确检查和取消检查)

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    //setting up nsUser
    userDefaults = [NSUserDefaults standardUserDefaults];

    //current row text
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    NSString *cellName = cell.textLabel.text;

    // Check if current row is selected
    Boolean isNowChecked = NO;
    if([tableView cellForRowAtIndexPath:indexPath].accessoryType == UITableViewCellAccessoryCheckmark)
    {
        isNowChecked = YES;
    }

    if(isNowChecked)
    {
        NSLog(@"UNCHECKING");
        [tableView cellForRowAtIndexPath:indexPath].accessoryType = UITableViewCellAccessoryNone;

        //takes away highlight from selection
        [tableView deselectRowAtIndexPath:indexPath animated:YES];

        //retrieve from nsdefaults
        NSMutableArray *arrayOfCategories = [userDefaults objectForKey:@"categories"];

        NSMutableArray *categoriesSelected;

        //remove from nsuserdefaults
        //add to nsuserdefaults
        for (NSString* o in arrayOfCategories)
        {
            NSLog(@"%@",o);
            if([o isEqualToString:cellName]) {

            } else {
                [categoriesSelected addObject:o];
            }

        }
        //set for nsdefaults
        [userDefaults setObject:categoriesSelected forKey:@"categories"];
        [userDefaults synchronize];


            }
    else
    {
        NSLog(@"CHECKING");
        [tableView cellForRowAtIndexPath:indexPath].accessoryType = UITableViewCellAccessoryCheckmark;

        //takes away highlight from selection
        [tableView deselectRowAtIndexPath:indexPath animated:YES];

        NSMutableArray *categoriesSelected;

        //add to array
        [categoriesSelected addObject:cellName];

        //retrieve from nsdefaults
        NSMutableArray *arrayOfCategories = [userDefaults objectForKey:@"categories"];

        //add to nsuserdefaults
        for (NSString* o in arrayOfCategories)
        {
            NSLog(@"%@",o);
            [categoriesSelected addObject:o];

        }
        //set for nsdefaults
        [userDefaults setObject:categoriesSelected forKey:@"categories"];
        [userDefaults synchronize];


    }
}

Answer 1

改变这一行，否则你有一个未初始化的数组:

NSMutableArray *categoriesSelected;

到:

NSMutableArray *categoriesSelected = [[NSMutableArray alloc] init];

更新:在查看您的代码后，实际上有很多地方需要改进。

1. 您应该在 viewDidLoad 中加载一次检查类别列表，并将列表保存在实例变量中。
2. 通过查看单元格的附件类型来检查单元格当前是否被选中不是一个好主意。您的数据模型应该告诉您检查了哪些行。
3. 您有很多重复代码来切换单元格的选中状态。
4. 使用集合而不是数组来跟踪选中的单元格。

尝试以下更改:

在你的类中添加一个 NSMutableSet 实例变量:

NSMutableSet *_checkedCategories;

在viewDidLoad中，加载集合:

NSArray *checkedCategories = [[NSUserDefault standardUserDefaults] objectForKey:@"categories"];
if (checkedCategories) {
    _checkedCategories = [[NSMutableSet alloc] initWithArray:checkedCategories];
} else {
    _checkedCategories = [[NSMutableSet alloc] init];
}

现在更新您的 didSelectRow 方法:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *cellName = ...; // get the cell name from your data model, not the cell

    BOOL isChecked = [_checkedCategories containsObject:cellName];

    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    if (isChecked) {
        [_checkedCategories removeObject:cellName]; // no longer checked
        cell.accessoryType = UITableViewCellAccessoryNone;
    } else {
        [_checkedCategories addObject:cellName]; // now checked
        cell.accessoryType = UITableViewCellAccessoryCheckmark;
    }

    [tableView deselectRowAtIndexPath:indexPath animated:YES];

    [[NSUserDefaults standardUserDefaults] setObject:[_checkedCategories allObjects] forKey:@"categories"];
    [[NSUserDefaults standardUserDefaults] synchronize];
}