working sample on both simple loading and transition.

lib/build.gradle

@@ -36,5 +36,5 @@ dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_ver"
     implementation 'androidx.core:core-ktx:1.1.0'
 
-    implementation "com.github.KirkBushman:subsampling-scale-image-view:$ssiv_ver"
+    api "com.github.KirkBushman:subsampling-scale-image-view:$ssiv_ver"
 }

lib/src/main/java/com/kirkbushman/largeimageview/ImageLoader.kt

@@ -5,11 +5,25 @@ import android.view.View
 
 interface ImageLoader {
 
-    fun getThumbnailView(context: Context): View
+    /**
+     * Receive from the user the view that binds to thumbnailView
+     */
+    fun getThumbnailView(context: Context): View?
+
+    /**
+     * Load the image to the View provided, the method is up to the user
+     */
     fun loadThumbnail(view: View, url: String)
 
-    fun preloadSource(url: String)
+    /**
+     * Receive from the user the view that binds to errorView
+     */
+    fun getErrorView(context: Context): View?
 
-    // fun onImageDownloaded(onLoaded: () -> Unit)
-    // fun onImageErrored(onErrored: () -> Unit)
+    /**
+     * Start preloading the large image as a java File,
+     * the method used is up to the user, use the callback to report if the image is available
+     * or the fetching went wrong.
+     */
+    fun preloadSource(url: String, callback: ImageReadyCallback)
 }

lib/src/main/java/com/kirkbushman/largeimageview/ImageReadyCallback.kt

@@ -0,0 +1,16 @@
+package com.kirkbushman.largeimageview
+
+import java.io.File
+
+interface ImageReadyCallback {
+
+    /**
+     * The large image preloaded is ready, as a java File Object
+     */
+    fun onImageReady(file: File, forceImageShow: Boolean = false)
+
+    /**
+     * The process did return an error.
+     */
+    fun onImageErrored()
+}

lib/src/main/java/com/kirkbushman/largeimageview/LargeImageView.kt

@@ -1,27 +1,29 @@
 package com.kirkbushman.largeimageview
 
 import android.content.Context
+import android.net.Uri
 import android.util.AttributeSet
 import android.view.View
 import android.view.ViewGroup
 import android.widget.FrameLayout
+import androidx.annotation.UiThread
+import com.davemorrissey.labs.subscaleview.ImageSource
 import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
+import java.io.File
 
 @Suppress("unused", "MemberVisibilityCanBePrivate")
-class LargeImageView @JvmOverloads constructor(
-    context: Context,
-    attrs: AttributeSet? = null,
-    defStyleAttr: Int = 0
-) : FrameLayout(context, attrs, defStyleAttr) {
-
-    private var loader: ImageLoader? = null
+class LargeImageView @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : FrameLayout(context, attrs, defStyleAttr) {
 
     private var thumbnailUrl: String? = null
     private var sourceUrl: String? = null
 
     private var thumbnailView: View? = null
+    private var errorView: View? = null
     private var sourceView: SubsamplingScaleImageView? = null
 
+    private var loader: ImageLoader? = null
+    private var viewsShownListener: OnViewsShownListener? = null
+
     private var showImageWhenAvailable = true
 
     init {
@@ -33,10 +35,14 @@ class LargeImageView @JvmOverloads constructor(
         typedArray.recycle()
     }
 
-    fun setImageLoader(loader: ImageLoader) {
+    fun setImageLoader(loader: ImageLoader?) {
         this.loader = loader
     }
 
+    fun getSsiv(): SubsamplingScaleImageView? {
+        return sourceView
+    }
+
     fun getShowImageWhenAvailable(): Boolean {
         return showImageWhenAvailable
     }
@@ -45,47 +51,171 @@ class LargeImageView @JvmOverloads constructor(
         this.showImageWhenAvailable = showImageWhenAvailable
     }
 
-    fun setThumbnail(thumbnailUrl: String) {
-        setImage(thumbnailUrl, null)
-    }
-
-    fun setImage(sourceUrl: String) {
-        setImage(null, sourceUrl)
+    fun setOnViewShownListener(viewsShownListener: OnViewsShownListener?) {
+        this.viewsShownListener = viewsShownListener
     }
 
     fun setImage(thumbnailUrl: String?, sourceUrl: String?) {
         this.thumbnailUrl = thumbnailUrl
         this.sourceUrl = sourceUrl
 
-        loadImage()
+        startLoading()
     }
 
-    private fun loadImage() {
+    fun triggerShowImage() {
 
-        if (loader == null) {
+        if (showImageWhenAvailable) {
             return
         }
 
-        thumbnailUrl?.let { thumbUrl ->
+        showImage()
+    }
+
+    private fun startLoading() {
+
+        clearViews()
+
+        loader?.let { loader ->
+
+            // show the thumbnail in the meantime,
+            // while the large image is loading in the background.
+            thumbnailUrl?.let { thumbUrl ->
+
+                thumbnailView = loader.getThumbnailView(context)
+                thumbnailView?.let { thumbView ->
+
+                    loader.loadThumbnail(thumbView, thumbUrl)
+
+                    showThumbnail()
+                }
+            }
+
+            // start loading in the background the real image.
+            sourceUrl?.let { url ->
+
+                sourceView = SubsamplingScaleImageView(context)
+                sourceView?.let { view ->
+
+                    loader.preloadSource(url, object : ImageReadyCallback {
+
+                        // if the image is ready set it in the SSIV
+                        //
+                        // if showImageWhenAvailable is set to true,
+                        // show the main image right away
+                        //
+                        // otherwise wait for triggerShowImage() to get called.
+                        //
+                        override fun onImageReady(file: File, forceImageShow: Boolean) {
+
+                            view.setImage(ImageSource.uri(Uri.fromFile(file)))
+
+                            if (showImageWhenAvailable || forceImageShow) {
+                                showImage()
+                            }
+                        }
+
+                        // if something went wrong, show the error view.
+                        override fun onImageErrored() {
+                            errorView = loader.getErrorView(context)
+                            errorView?.let { _ ->
+
+                                showErrorView()
+                            }
+                        }
+                    })
+                }
+            }
+        }
+    }
+
+    fun clearViews() {
+        if (childCount > 0) {
+            removeAllViews()
+        }
+
+        thumbnailView = null
+        errorView = null
+        sourceView = null
+    }
 
-            thumbnailView = loader!!.getThumbnailView(context)
-            thumbnailView?.let { thumbView ->
+    @UiThread
+    private fun showThumbnail() {
 
-                loader!!.loadThumbnail(thumbView, thumbUrl)
+        if (thumbnailView != null) {
+            if (findViewById<View>(thumbnailView!!.id) == null) {
 
-                addView(thumbnailView,
+                addView(
+                    thumbnailView,
                     ViewGroup.LayoutParams.MATCH_PARENT,
-                    ViewGroup.LayoutParams.MATCH_PARENT)
+                    ViewGroup.LayoutParams.MATCH_PARENT
+                )
             }
+
+            viewsShownListener?.onThumbnailViewShown(thumbnailView!!)
         }
 
-        sourceUrl?.let { url ->
+        if (thumbnailView?.visibility != View.VISIBLE) {
+            thumbnailView?.visibility = View.VISIBLE
+        }
+    }
 
-            sourceView = SubsamplingScaleImageView(context)
-            sourceView?.let { view ->
+    @UiThread
+    private fun showErrorView() {
 
-                loader!!.preloadSource(url)
+        if (errorView != null) {
+            if (findViewById<View>(errorView!!.id) == null) {
+
+                addView(
+                    errorView,
+                    ViewGroup.LayoutParams.MATCH_PARENT,
+                    ViewGroup.LayoutParams.MATCH_PARENT
+                )
             }
+
+            viewsShownListener?.onErrorViewShown(errorView!!)
+        }
+
+        if (errorView?.visibility != View.VISIBLE) {
+            errorView?.visibility = View.VISIBLE
+        }
+
+        if (childCount > 0) {
+
+            postDelayed({
+
+                sourceView?.visibility = View.GONE
+                thumbnailView?.visibility = View.GONE
+            }, 1000)
+        }
+    }
+
+    @UiThread
+    private fun showImage() {
+
+        if (sourceView != null) {
+            if (findViewById<View>(sourceView!!.id) == null) {
+
+                addView(
+                    sourceView,
+                    ViewGroup.LayoutParams.MATCH_PARENT,
+                    ViewGroup.LayoutParams.MATCH_PARENT
+                )
+            }
+
+            viewsShownListener?.onImageViewShown(sourceView!!)
+        }
+
+        if (sourceView?.visibility != View.VISIBLE) {
+            sourceView?.visibility = View.VISIBLE
+        }
+
+        if (childCount > 0) {
+
+            postDelayed({
+
+                errorView?.visibility = View.GONE
+                thumbnailView?.visibility = View.GONE
+            }, 1000)
         }
     }
 }

lib/src/main/java/com/kirkbushman/largeimageview/OnViewsShownListener.kt

@@ -0,0 +1,22 @@
+package com.kirkbushman.largeimageview
+
+import android.view.View
+import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
+
+interface OnViewsShownListener {
+
+    /**
+     * Called after the thumbnail view is attached as children and shown
+     */
+    fun onThumbnailViewShown(view: View)
+
+    /**
+     * Called after the image view is attached as children and shown
+     */
+    fun onImageViewShown(view: SubsamplingScaleImageView)
+
+    /**
+     * Called after the error view is attached as children and shown
+     */
+    fun onErrorViewShown(view: View)
+}

sampleapp/src/main/AndroidManifest.xml

@@ -2,6 +2,9 @@
     xmlns:tools="http://schemas.android.com/tools"
     package="com.kirkbushman.largeimageview.sampleapp">
 
+    <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+
     <application
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
@@ -19,14 +22,16 @@
             </intent-filter>
         </activity>
 
-        <activity android:name=".BasicActivity"
+        <activity android:name=".activities.BasicActivity"
             android:parentActivityName=".MainActivity" />
 
-        <activity android:name=".AnimFirstActivity"
-            android:parentActivityName=".MainActivity" />
+        <activity android:name=".activities.AnimFirstActivity"
+            android:parentActivityName=".MainActivity"
+            android:theme="@style/TransitionTheme" />
 
-        <activity android:name=".AnimSecondActivity"
-            android:parentActivityName=".AnimFirstActivity" />
+        <activity android:name=".activities.AnimSecondActivity"
+            android:parentActivityName=".activities.AnimFirstActivity"
+            android:theme="@style/TransitionTheme" />
 
 
     </application>