NSArrayController没有将大型数据集加载到数组中 [英] NSArrayController without loading a large dataset into an array

问题描述

我想使用NSArrayController向NSTableView提供数据。我面临的问题是，我不想预先加载所有的数据到数组，然后使用数组控制器 setContent：方法。我的数据模型是一个大型的现有代码库，管理着数百万条记录。它包含有效地返回一组数据行的方法。

我发现了一个限制NSArrayController中对象数量的例子，我试图子类化NSArrayController并覆盖 arrangeObjects：方法返回一个数组代理类我写的。数组代理类提供了 count：和 objectAtIndex：方法。 objectAtIndex：返回的对象是NSDictionary。当我尝试从 arrangeObjects：方法返回我的数组代理 count：和 objectAtIndex： 得到调用，但我也得到一个无法识别的选择器错误在我的数组代理类 _valueForKeyPath：ofObjectAtIndex：。这看起来像一个私有方法，所以我没有继续沿着这条路。

我还想到从 arrangeObjects：返回一个较小的数据数组，确定NSTableView尝试显示哪些行。

是一个数据源是正确的方式与我现有的数据模型接口，还是有一些方法使NSArrayController工作？

< NSArrayController已经工作，代理和索引，延迟加载和整个shabang。你试过只是使用它是什么？如果之后你觉得需要微管理数据加载，请使用NSFetchRequest。子类NSArrayController，并沿着这些行添加一个初始化器：

  +（id）arrayControllerWithEntityName：（NSString *）entityName error： *）error 
 {
 id newInstance = [[[self alloc] initWithContent：nil] autorelease]; 
 
 [newInstance setManagedObjectContext：[[NSApp delegate] managedObjectContext]]; 
 [newInstance setEntityName：entityName]; 
 
 [newInstance setAutomaticallyPreparesContent：YES]; 
 [newInstance setSelectsInsertedObjects：YES]; 
 [newInstance setAvoidsEmptySelection：YES]; 
 [newInstance setAlwaysUsesMultipleValuesMarker：YES]; 
 
 NSFetchRequest * dontGobbleRequest = [[[NSFetchRequest alloc] init] autorelease]; 
 //使用fetchLimit和fetchOffset配置请求所有
 NSError * err; 
 if（[newInstance fetchWithRequest：dontGobbleRequest merge：YES error：& err] == NO）{
 //更好地检查文档是否合并：YES是你想要的
 if &&&& err）{
 * error = err; 
} 
 return nil; 
} 
 
 return newInstance; 
} 
  

您必须对各种可能性和配置进行一些研究，你得到的图片。

I would like to use an NSArrayController to provide data to an NSTableView. The problem I am facing is that I do not want to pre-load all my data into an array and then use the array controllers setContent: method. My data model is a large existing code base that manages millions of records. It contains methods to efficiently return a set of data rows.

Following an example I found on limiting the number of objects in an NSArrayController, I tried subclassing NSArrayController and overriding the arrangedObjects: method to return an array proxy class I wrote. The array proxy class provided count: and objectAtIndex: methods. The object returned by objectAtIndex: is an NSDictionary. When I tried returning my array proxy from the arrangedObjects: method both count: and objectAtIndex: get called, but I also get an unrecognized selector error on my array proxy class for _valueForKeyPath:ofObjectAtIndex:. This looked like a private method, so I did not continue down this path.

I also thought of returning a smaller array of data from arrangedObjects:, but could not figure out how I would determine which rows the NSTableView was trying to display.

Is a datasource the "correct" way to interface with my existing data model or is there some way to make an NSArrayController work?

解决方案

NSArrayController already works, with proxies and indexes and lazy-loading and the whole shabang. Have you tried just using it as-is? If afterwards you feel the need to micro-manage the data-loading, use NSFetchRequest. Subclass NSArrayController and add an initializer along these lines:

+ (id)arrayControllerWithEntityName: (NSString *)entityName error:(NSError **)error
{
    id newInstance = [[[self alloc] initWithContent:nil] autorelease];

    [newInstance setManagedObjectContext:[[NSApp delegate] managedObjectContext]];
    [newInstance setEntityName:entityName];

    [newInstance setAutomaticallyPreparesContent:YES];
    [newInstance setSelectsInsertedObjects:YES];
    [newInstance setAvoidsEmptySelection:YES];
    [newInstance setAlwaysUsesMultipleValuesMarker:YES];

    NSFetchRequest *dontGobbleRequest = [[[NSFetchRequest alloc] init] autorelease];
    //configure the request with fetchLimit and fetchOffset an' all that
    NSError *err;
    if ([newInstance fetchWithRequest:dontGobbleRequest merge:YES error:&err] == NO) {
        //better check docs whether merge:YES is what you want
        if(*error && err) {
            *error = err;
        }
        return nil;
    }

    return newInstance; 
}

You'll have to do some research into the various possibilities and configurations, but you get the picture.

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