glide-extension.md

Glide extension

Glide calls like this are rather verbose by Kotlin standards, even though the library actually has a very neat API:

Glide.with(companyLogoImage).load(job.companyLogo).into(companyLogoImage)

It's not hard to imagine an extension function that would allow you to quickly and easily put an image by its URL into an ImageView, using Glide internally:

companyLogoImage.load(job.companyLogo)

Let's create a new top level util package within our project, and within that, a file named Glide.kt, since we'll place Glide related extensions here. Instead of going for a trivial implementation, we'll do something fancier to show off some Kotlin features:

inline fun ImageView.load(path: String?, withCache: Boolean = true) {
    if (path == null) {
        setImageDrawable(null)
        return
    }

    val requestManager = Glide.with(this)

    if (!withCache) {
        requestManager.applyDefaultRequestOptions(
                RequestOptions()
                        .skipMemoryCache(true)
                        .diskCacheStrategy(DiskCacheStrategy.NONE))

    }

    requestManager.load(path).into(this)
}

Now, what's all this code if we're only trying to replace the one-liner of a Glide load we've seen earlier?

We've added some extra features here. In the case of receiving a null path in the parameter, we're setting a null value as an ImageDrawable into the ImageView directly, instead of having Glide fail to load it when we invoke it.

The function also has an extra withCache parameter which has a default value, making it essentially optional at the call site. By default, this parameter is true, and does essentially nothing. However, if set to false, it will circumvent Glide's memory and disk cache, and always fully reload the image from its source. We don't need this functionality in this project, but it's useful if, for example, you're modifying an image file on disk in place, and want those changes reflected immediately when loading it into an ImageView.

Optimization fun

What's even more interesting here is that if we try calling this inline function with a true and a false value for this parameter, we'll see that the if check for this parameter is never actually generated in the inlined code. If the value is known at compile time, the compiler will simply inline the appropriate branches as an optimization.

For example, this call:

companyLogoImage.load(job.companyLogo)

... generates the following in the bytecode (this is Kotlin code, based on the decompiled Java from bytecode):

val path = job.companyLogo
if (path == null) {
    companyLogoImage.setImageDrawable(null)
} else {
    val requestManager: RequestManager = Glide.with(companyLogoImage)
    requestManager.load(path).into(companyLogoImage)
}

And this one:

companyLogoImage.load(job.companyLogo, withCache = false)

... generates this:

val path = job.companyLogo
if (path == null) {
    companyLogoImage.setImageDrawable(null)
} else {
    val requestManager: RequestManager = Glide.with(companyLogoImage)
    requestManager.applyDefaultRequestOptions(RequestOptions().skipMemoryCache(true)
                                              .diskCacheStrategy(DiskCacheStrategy.NONE))
    requestManager.load(path).into(companyLogoImage)
}

No if check for withCache anywhere!

Usage

Let's actually use this new extension in our project now. There are two Glide calls we can update.

First, in JobDetailFragment's showJobDetails method:

companyLogoImage.load(job.companyLogo)

And then in onBindViewHolder inside JobListingAdapter, where we load the images for the list items:

holder.image.load(jobListing.imageUrl)

Continue...

Next, some Android Studio tooling tips.