For images you create in your WatchKit extension but use frequently, Apple recommends caching those images on the device and refer to them by name. There are some basic functions like addCachedImage:name: or removeCachedImageWithName: to manage this. This is nice, but you have to take care of removing old images to free up a full cache (about 5MB per app) all by yourself.
The WKImageCache doesn't replace that cache, it's merely a simple wrapper that tries to solve this problem. If the user wants to add a new image and the cache is full, the WKImageCache automatically removes previous images based on currently two strategies, FIFO and LRU.
Take a look at the Example project to see how to use it.
WKImageCache requires iOS8.2 or above.
Copy the WKImageCache.swift file to your Swift project and add it to your target. After that you need to (if not already exists) create a bridging header by choosing File > New > File > iOS > Source > Header File and name it projectname-bridging-header.h. Then add the following line and you're good to go:
#import <CommonCrypto/CommonCrypto.h>WKImageCache provides extensions for three interface types that currently support displaying images: WKInterfaceImage, WKInterfaceButton and WKInterfaceGroup.
For example, if you want to display an image (using the WKInterfaceImage) and cache it for later usage, you would use the following method:
interfaceImage.setCachedImage(image)The image will be compressed, transmitted and added to the cache. If the image is already chached, this version will be used. There are additional (optional) parameters that you can use for adjusting the behaviour:
interfaceImage.setCachedImage(image, compression: 0.6, cacheType: .LRU)- The compression (0.6 is default) is applied to the image before transmitting it. The lower the compression value, the faster the transmission.
- The default cache type is FIFO, which means that the oldest image in the cache will be removed if there's no space left. Alternatively, you can use LRU, which discards the least recently used images first.
If the image is available as NSData, use this function:
interfaceImage.setCachedImageData(data)The functions for WKInterfaceButton and WKInterfaceGroup are called
- setCachedBackgroundImage(image : UIImage)
- setCachedBackgroundImageData(image : UIImage)
and work equally.
WKImageCache is available under the MIT license. See the LICENSE file for more info.
The release notes can be found here.
- Code Documentation