一個(gè)舊項(xiàng)目需要添加僅wifi下加載圖片的配置功能，因?yàn)樵擁?xiàng)目并沒有封裝圖片加載，只是直接使用了glide加載圖片，常規(guī)改造方法工作量巨大，于是有了這篇。

實(shí)現(xiàn)思路是通過自定義的Loader，實(shí)現(xiàn)wifi下正常邏輯，非wifi下跳過下載流程。
官方文檔，https://muyangmin.github.io/glide-docs-cn/tut/custom-modelloader.html

自定義Fetcher

這個(gè)類是圖片下載的核心邏輯。

class NewsFetcher(private val client: Call.Factory, private val url: GlideUrl) :
    DataFetcher<InputStream>, okhttp3.Callback {

    private val TAG = NewsFetcher::class.java.name

    @Volatile
    private var call: Call? = null
    private var callback: DataFetcher.DataCallback<in InputStream>? = null
    private var stream: InputStream? = null
    private var responseBody: ResponseBody? = null


    override fun loadData(priority: Priority, callback: DataFetcher.DataCallback<in InputStream>) {
        if (不滿足下載圖片的情況) {
            return
        }
        //使用okhttp 請(qǐng)求圖片
        val requestBuilder = Request.Builder().url(url.toStringUrl())
        for ((key, value) in url.headers) {
            requestBuilder.addHeader(key, value)
        }
        val request = requestBuilder.build()
        this.callback = callback
        call = client.newCall(request)
        call?.enqueue(this)
    }

    override fun cleanup() {
        try {
            stream?.close()
        } catch (e: IOException) {
            // Ignored
        }
        responseBody?.close()
        callback = null
    }

    override fun cancel() {
        val local = call
        local?.cancel()
    }

    override fun getDataClass(): Class<InputStream> = InputStream::class.java

    override fun getDataSource(): DataSource = DataSource.REMOTE

    override fun onFailure(call: Call, e: IOException) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "OkHttp failed to obtain result", e)
        }
        callback?.onLoadFailed(e)

    }

    override fun onResponse(call: Call, response: Response) {
        responseBody = response.body()
        if (response.isSuccessful) {
            val contentLength =
                Preconditions.checkNotNull(responseBody).contentLength()
            stream = ContentLengthInputStream.obtain(responseBody!!.byteStream(), contentLength)
            callback?.onDataReady(stream)
        } else {
            callback?.onLoadFailed(HttpException(response.message(), response.code()))
        }

    }
}

ModelLoader

1. 定義一個(gè)okhttp單例

object NewsInternalClient {
    val internalClient: Call.Factory = OkHttpClient()
}

2. modelLoader

class NewsModelLoader(private val client: Call.Factory) : ModelLoader<GlideUrl, InputStream> {

    override fun handles(url: GlideUrl): Boolean {
        return true
    }

    override fun buildLoadData(
        model: GlideUrl,
        width: Int,
        height: Int,
        options: Options
    ): ModelLoader.LoadData<InputStream>? {
        return ModelLoader.LoadData(model,
            NewsFetcher(client, model)
        )
    }

    class Factory : ModelLoaderFactory<GlideUrl, InputStream> {

        override fun build(multiFactory: MultiModelLoaderFactory): ModelLoader<GlideUrl, InputStream> {
            return NewsModelLoader(NewsInternalClient.internalClient)
        }

        override fun teardown() {
            // Do nothing, this instance doesn't own the client.
        }
    }

}

LibraryGlideModule

因?yàn)槲业倪壿嬍窃趍odule中，所以使用LibraryGlideModule，如果你的實(shí)在app module則使用AppGlideModule。

@GlideModule
class NewsGlideModel : LibraryGlideModule() {

    override fun registerComponents(context: Context, glide: Glide, registry: Registry) {
        registry.replace(
            GlideUrl::class.java, InputStream::class.java,
            NewsModelLoader.Factory()
        )
    }
}

最后

到這里你的配置還不會(huì)生效，需要在app module中編寫一個(gè)空的AppGlideModule

@GlideModule
public class MyAppGlideModel extends AppGlideModule {
}

在使用到glide注解的模塊添加處理器
kapt 'com.github.bumptech.glide:compiler:4.11.0'

大功告成，正常使用glide即可。