如何使用NSCache

有人可以举例说明如何使用NSCache缓存字符串吗？还是有人有一个很好的解释链接？我似乎找不到任何..

使用方法与使用方法相同NSMutableDictionary。区别在于，当NSCache检测到过多的内存压力（即，缓存了太多的值）时，它将释放其中的一些值以腾出空间。

如果您可以在运行时重新创建这些值（通过从Internet下载，进行计算等方法），则NSCache可能满足您的需求。如果无法重新创建数据（例如，用户输入，对时间敏感等），则不应将其存储在NSCache因为它将在此处被破坏。

示例，未考虑线程安全性：

// Your cache should have a lifetime beyond the method or handful of methods
// that use it. For example, you could make it a field of your application
// delegate, or of your view controller, or something like that. Up to you.
NSCache *myCache = ...;
NSAssert(myCache != nil, @"cache object is missing");

// Try to get the existing object out of the cache, if it's there.
Widget *myWidget = [myCache objectForKey: @"Important Widget"];
if (!myWidget) {
    // It's not in the cache yet, or has been removed. We have to
    // create it. Presumably, creation is an expensive operation,
    // which is why we cache the results. If creation is cheap, we
    // probably don't need to bother caching it. That's a design
    // decision you'll have to make yourself.
    myWidget = [[[Widget alloc] initExpensively] autorelease];

    // Put it in the cache. It will stay there as long as the OS
    // has room for it. It may be removed at any time, however,
    // at which point we'll have to create it again on next use.
    [myCache setObject: myWidget forKey: @"Important Widget"];
}

// myWidget should exist now either way. Use it here.
if (myWidget) {
    [myWidget runOrWhatever];
}

@implementation ViewController
{    
    NSCache *imagesCache;    
}


- (void)viewDidLoad
{    
    imagesCache = [[NSCache alloc] init];
}


// How to save and retrieve NSData into NSCache
NSData *imageData = [imagesCache objectForKey:@"KEY"];
[imagesCache setObject:imageData forKey:@"KEY"];

在Swift中使用NSCache缓存字符串的示例代码：

var cache = NSCache()
cache.setObject("String for key 1", forKey: "Key1")
var result = cache.objectForKey("Key1") as String
println(result) // Prints "String for key 1"

要创建单个应用程序范围的NSCache实例（单个实例），可以轻松扩展NSCache以添加sharedInstance属性。只需将以下代码放在一个名为NSCache + Singleton.swift之类的文件中：

import Foundation

extension NSCache {
    class var sharedInstance : NSCache {
        struct Static {
            static let instance : NSCache = NSCache()
        }
        return Static.instance
    }
}

然后，您可以在应用程序中的任何位置使用缓存：

NSCache.sharedInstance.setObject("String for key 2", forKey: "Key2")
var result2 = NSCache.sharedInstance.objectForKey("Key2") as String
println(result2) // Prints "String for key 2"

示例项目 将示例项目中的 CacheController.h和.m文件添加到您的项目中。在要缓存数据的类中，输入以下代码。

[[CacheController storeInstance] setCache:@"object" forKey:@"objectforkey" ];

您可以使用此设置任何对象

[[CacheController storeInstance] getCacheForKey:@"objectforkey" ];

取回

重要提示：NSCache类包含各种自动删除策略。如果要永久存储数据或要在特定时间内删除缓存的数据， 请参见此答案。

缓存的对象不应该实现NSDiscardableContent协议吗？

从NSCache类参考中：存储在NSCache对象中的常见数据类型是实现NSDiscardableContent协议的对象。将此类对象存储在缓存中有很多好处，因为可以在不再需要它的内容时将其内容丢弃，从而节省了内存。默认情况下，如果丢弃了缓存中的NSDiscardableContent对象，则它们的内容将被自动删除，尽管可以更改此自动删除策略。如果将NSDiscardableContent对象放入缓存，则缓存在删除后会对其调用discardContentIfPossible。