implementation 'com.github.iielse:imageviewer:x.y.z'

fun show() { //
    val dataList： List<Photo> = // 将要展示的图片集合列表
    val clickedData: Photo = // 被点击的其中的那个图片元素信息
    val builder = ImageViewerBuilder(
        context = view.context,
        initKey = clickedData.id, // photoId
        dataProvider = SimpleDataProvider(dataList), // 一次性全量加载 // 实现DataProvider接口支持分页加载
        imageLoader = SimpleImageLoader(), // 可使用demo固定写法 // 实现对数据源的加载.支持自定义加载数据类型，加载方案
        transformer = SimpleTransformer(), // 可使用demo固定写法 // 以photoId为标示，设置过渡动画的'配对'.
    )
    builder.show()
}

// 基本是固定写法. Glide 可以换成别的. demo代码中有video的写法.
class SimpleImageLoader : ImageLoader {
    /** 根据自身photo数据加载图片.可以使用其它图片加载框架. */
    override fun load(view: ImageView, data: Photo, viewHolder: RecyclerView.ViewHolder) {
        val it = (data as? MyData?)?.url ?: return
        Glide.with(view).load(it)
                .placeholder(view.drawable)
                .into(view)
    }

    /**
     * 根据自身photo数据加载超大图.subsamplingView数据源需要先将内容完整下载到本地.
     */
    override fun load(subsamplingView: SubsamplingScaleImageView, data: Photo, viewHolder: RecyclerView.ViewHolder) {
        val it = (data as? MyData?)?.url ?: return
        subsamplingDownloadRequest(it)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .doOnSubscribe { findLoadingView(viewHolder)?.visibility = View.VISIBLE }
                .doFinally { findLoadingView(viewHolder)?.visibility = View.GONE }
                .doOnNext { subsamplingView.setImage(ImageSource.uri(Uri.fromFile(it))) }
                .doOnError { toast(it.message) }
                .subscribe().bindLifecycle(subsamplingView)
    }

    private fun subsamplingDownloadRequest(url: String): Observable<File> {
        return Observable.create {
            try {
                it.onNext(Glide.with(appContext).downloadOnly().load(url).submit().get())
                it.onComplete()
            } catch (e: java.lang.Exception) {
                if (!it.isDisposed) it.onError(e)
            }
        }
    }

    private fun findLoadingView(viewHolder: RecyclerView.ViewHolder): View? {
        return viewHolder.itemView.findViewById<ProgressBar>(R.id.loadingView)
    }

    ......
}

// 基本是可以作为固定写法.
class SimpleTransformer : Transformer {
    override fun getView(key: Long): ImageView? = ViewerTransitionHelper.provide(key)
}

/**
 * 维护Transition过渡动画的缩略图和大图之间的映射关系.
 */
object ViewerTransitionHelper {
    private val transition = HashMap<ImageView, Long>()
    fun put(photoId: Long, imageView: ImageView) { // 将photoId和展示这个数据的ImageView'绑定'
        require(isMainThread())
        if (!imageView.isAttachedToWindow) return
        imageView.addOnAttachStateChangeListener(object : View.OnAttachStateChangeListener {
            override fun onViewAttachedToWindow(p0: View?) = Unit
            override fun onViewDetachedFromWindow(p0: View?) {
                transition.remove(imageView)
                imageView.removeOnAttachStateChangeListener(this)
            }
        })
        transition[imageView] = photoId
    }

    fun provide(photoId: Long): ImageView? {
        transition.keys.forEach {
            if (transition[it] == photoId)
                return it
        }
        return null
    }
}

// 一般监听翻页onPageSelected可以控制 video播放的状态
// viewer 各状态监听回调
interface ViewerCallback : ImageViewerAdapterListener {
    // 当点击缩略图变化大图的瞬间
    override fun onInit(viewHolder: RecyclerView.ViewHolder) {}
    // 当图片被拖动时
    override fun onDrag(viewHolder: RecyclerView.ViewHolder, view: View, fraction: Float) {}
    // 当图片被拖动但不至于退出浏览
    override fun onRestore(viewHolder: RecyclerView.ViewHolder, view: View, fraction: Float) {}
    // 当图片被拖动执行退出浏览
    override fun onRelease(viewHolder: RecyclerView.ViewHolder, view: View) {}
    // 翻页中状态变化
    fun onPageScrollStateChanged(state: Int) {}
    // 翻页中
    fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}
    // 当某大图页面被选中
    fun onPageSelected(position: Int, viewHolder: RecyclerView.ViewHolder) {}
}

interface Photo {
    fun id(): Long // 每条图片数据的唯一标示. 主要用于分页数据加载. 定位过渡动画的对应关系
    fun itemType(): @ItemType.Type Int // 是否启用SubsamplingScaleImageView实现图片区块加载或ExoVideoView实现Video加载
}