NSPredicate在NSDictionary [英] NSPredicate on NSDictionary

问题描述

我正在尝试根据字母在表视图中创建节，并在这些节下按字母顺序对条目进行排序.

I'm trying to make sections in a table view based on the alphabet and sort my entries alphabetically under these sections.

我已经在bandsArrayIndex中的bandsArray的每个条目中收集了第一个字母，现在我正尝试使用NSPredicate来计算每个字母中有多少个.

I have collected the first letter in every entry of bandsArray in bandsArrayIndex and I'm now trying to use NSPredicate to count how many of each letter there are.

我正在按照本指南进行操作.

他们正在使用NSArray，而我正在使用NSDictionary，似乎无法使其正常工作.有人可以帮我吗?

They are using an NSArray and I'm using an NSDictionary and can't seem to get it to work. Can anyone help me out?

尝试在其中显示带有表格视图的视图时，应用程序崩溃. 在调试器控制台中，显示以下错误:

The application crashes when trying to show the view with the table view in it. In Debugger Console the following error is shown:

* 由于未捕获的异常而终止应用程序 "NSInvalidArgumentException"，原因: '无法使用 不是字符串的东西

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Can't do a substring operation with something that isn't a string

这是我的代码

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSString *alphabet = [bandsArrayIndex objectAtIndex:section];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] %@", alphabet];
    NSArray *letters = [bandsArray filteredArrayUsingPredicate:predicate];

    return [letters count];
}

这是我的bandsArray.

This is my bandsArray.

标题

NSMutableArray *bandsArray;

@property (nonatomic, retain) NSMutableArray* bandsArray;

实施

// set array from plist
NSString *path = [[NSBundle mainBundle] pathForResource:@"Bands" ofType:@"plist"];
NSMutableArray* tmpArray = [[NSMutableArray alloc] initWithContentsOfFile:path];

self.bandsArray = tmpArray;

// sort array after name ascending
NSSortDescriptor *nameSorter = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES selector:@selector(caseInsensitiveCompare:)];
[bandsArray sortUsingDescriptors:[NSArray arrayWithObject:nameSorter]];

推荐答案

您是说bandsArray是一个字典数组吗?如果是这样，并假设每个词典都有一个name键，则您应该可以将谓词更改为类似@"SELF.name beginswith[c] %@"的谓词.

Do you mean that bandsArray is an array of dictionaries? If so, and assuming each dictionary has a name key, you should be able to change the predicate to something like @"SELF.name beginswith[c] %@".

反之，如果bandsArray实际上是字典本身，那么也许您想做[[bandsArray allKeys] filteredArrayUsingPredicate...].

If, on the other hand, bandsArray is actually a dictionary itself, maybe you want to do [[bandsArray allKeys] filteredArrayUsingPredicate...].

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