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我想更改此属性列表中的值profileData.plist：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>profiles</key>
    <array>
        <dict>
            <key>Name</key>
            <string>Default Profile</string>
            <key>size</key>
            <integer>0</integer>
        </dict>
    </array>
    <key>settings</key>
    <dict>
        <key>length</key>
        <string>cm</string>
    </dict>
</dict>
</plist>

我想将键的整数设置size为1. 我已经这样做了：

// reading Property List as described in Property List Programming Guide
NSError *error = nil;
NSPropertyListFormat format;
NSString *plistPath;
NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                     NSUserDomainMask, YES) objectAtIndex:0];
plistPath = [rootPath stringByAppendingPathComponent:@"profileData.plist"];
if (![[NSFileManager defaultManager] fileExistsAtPath:plistPath]) {
    plistPath = [[NSBundle mainBundle] pathForResource:@"profileData" ofType:@"plist"];
}
NSData *plistXML = [[NSFileManager defaultManager] contentsAtPath:plistPath];
NSMutableDictionary *temp = (NSMutableDictionary *)[NSPropertyListSerialization
                                      propertyListWithData:plistXML
                                      options:NSPropertyListMutableContainersAndLeaves
                                      format:&format
                                      error:&error];
if (!temp) {
    DNSLog(@"Error reading plist: %@, format: %ld", error, (long)format);
}

// getting the right dictionary
NSMutableArray *profiles = [temp objectForKey:@"profiles"];
NSMutableDictionary profile0 = [profiles objectAtIndex:0];

// Setting new integer
[profile0 setObject:[NSNumber numberWithInt:1] forKey:@"size"];

// saving objects in reverse
[profiles replaceObjectAtIndex:0 withObject:profile0];
[temp setObject:profiles forKey:@"profiles"];

// writing property list
[temp writeToFile:plistPath atomically:YES];

此代码有效。

我的问题：这是最好的方法吗？从磁盘读取属性列表是可以的。但是是否有必要将属性列表的所有“级别”保存在单独的可变对象中，然后将所有这些对象反向设置到属性列表的最高级别？

对我来说，以这种方式执行此操作似乎有点复杂，即使我想象一个具有更多级别的属性列表。如果可以以这种方式做到这一点，那就太好了：

[temp setObject:[NSNumber numberWithInt:1] forKeyPath:@"profiles.0.size"];
4

1 回答 1

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/*The nature of using a plist or XML in XCode requires you to load the entire contents of the file into memory before doing anything with it (unless you're using a 3rd-party DOM parser for XML), just as you've done here. NSArray & NSDictionary then have the `writeToFile: atomically:` method you're already using to write changes back to disk. 

Of course you can access and change the temp NSMutableDictionary at whichever level you like, but if you want to save the changes then this is pretty much how you have to do it. 

As you imagined, this can be bad for larger/complex data or if you're saving changes all the time. 

I'd suggest you refactor this into multiple methods - right now you're loading the data, making the changes, AND writing back out to file all in the same place, which means you have to do all of that each time.

Break things up so you can do these tasks independently:

 - load plist from disk 
 - create temp copy of plist data as @property
 - make a change to tempdata @property (passing in whatever argument you need); 
 - write changes to disk

This would allow you to make multiple changes to the temp data as needed & only update the data model on disk when you have a bunch to do at once or need to ensure it's up to date (say, before the app goes into the background). This would cut the # of read/writes, but requires you to consider how fresh you need your data model to be & when's the best time to update the changes. 

If you're not stuck w/using plists, you could also look into using JSON, which is faster & lighter, and XCode now has pretty good native support, but writing to a file is the exact same process. For persisting larger, more complex data sets and making easier changes to individual items you might want to consider CoreData.   

..................................
1 other note ... In these lines: 

    NSMutableArray *profiles = [temp objectForKey:@"profiles"];
    NSMutableDictionary profile0 = [self.profiles objectAtIndex:0];

You're declaring `*profiles` within the method, not as a property of the object, so you shouldn't refer to it as `self.profiles`. Surprised this works w/o causing an error (unless you have both? In that case it won't work as expected). After refactoring to separate methods an @property is what you'll want.*/

根据以下评论进行编辑：

我明白了-在这种情况下，您上面的建议似乎很接近，但是方法名称是setValue:(id) forKeyPath:(NSString *), not setObject...。此外，您可以对 NSNumber 使用 Obj-C 文字语法。

也许尝试类似： [temp setValue:@1 forKeyPath:@"temp.profiles.0.size"];

（注意：尚未对此进行测试。不确定您是否需要包含temp在 keyPath 中的完整路径）。请参阅 Apple 的KVC 编程指南和KVC 协议参考

我认为这种方法不会对速度或性能产生明显影响，但我还没有测试过。这也假设您正在访问的对象绝对是带有这些特定键的字典。如果结构或键发生变化，则此处没有自省或错误处理。您的初始方法的一个好处是您可以明确了解他们可以访问的对象类型和方法/属性，而这是一种开放式的。

于 2014-07-17T16:51:29.690 回答