Added RetainingImageSource to simplify replacing a given image on screen

Summary:
This adds a new `RetainingImageSource` that can be used to retain the image until the next image source is available.

Usage:

```
val retainingImageSource = RetainingImageSource(initialImageSource)

// at some point update the image source via:

retainingImageSource.updateImageSource(newImageSource);
```

Reviewed By: kartavya-ramnani

Differential Revision: D73676558

fbshipit-source-id: a30244138548ff484b9f2e413248c2081981d085

Author: oprisnik

samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/vito/RetainingDataSourceSupplierFragment.java

@@ -14,16 +14,12 @@
 import android.view.ViewGroup;
 import android.widget.ImageView;
 import androidx.annotation.Nullable;
-import com.facebook.common.references.CloseableReference;
-import com.facebook.datasource.RetainingDataSourceSupplier;
-import com.facebook.drawee.backends.pipeline.Fresco;
 import com.facebook.fresco.samples.showcase.BaseShowcaseFragment;
 import com.facebook.fresco.samples.showcase.R;
-import com.facebook.fresco.vito.core.impl.source.DataSourceImageSource;
+import com.facebook.fresco.vito.core.impl.source.RetainingImageSource;
 import com.facebook.fresco.vito.options.ImageOptions;
+import com.facebook.fresco.vito.source.ImageSourceProvider;
 import com.facebook.fresco.vito.view.VitoView;
-import com.facebook.imagepipeline.image.CloseableImage;
-import com.facebook.imagepipeline.request.ImageRequest;
 import java.util.List;
 
 public class RetainingDataSourceSupplierFragment extends BaseShowcaseFragment {
@@ -51,23 +47,14 @@ public View onCreateView(
   @Override
   public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
     final ImageView imageView = view.findViewById(R.id.image_view);
-    final RetainingDataSourceSupplier<CloseableReference<CloseableImage>> retainingSupplier =
-        new RetainingDataSourceSupplier<>();
-    VitoView.show(
-        new DataSourceImageSource(retainingSupplier), mImageOptions, CALLER_CONTEXT, imageView);
-    replaceImage(retainingSupplier);
-    imageView.setOnClickListener(v -> replaceImage(retainingSupplier));
+    final RetainingImageSource imageSource = new RetainingImageSource();
+    VitoView.show(imageSource, mImageOptions, CALLER_CONTEXT, imageView);
+    replaceImage(imageSource);
+    imageView.setOnClickListener(v -> replaceImage(imageSource));
   }
 
-  private void replaceImage(
-      RetainingDataSourceSupplier<CloseableReference<CloseableImage>> retainingSupplier) {
-
-    retainingSupplier.replaceSupplier(
-        Fresco.getImagePipeline()
-            .getDataSourceSupplier(
-                ImageRequest.fromUri(getNextUri()),
-                CALLER_CONTEXT,
-                ImageRequest.RequestLevel.FULL_FETCH));
+  private void replaceImage(RetainingImageSource retainingImageSource) {
+    retainingImageSource.updateImageSource(ImageSourceProvider.forUri(getNextUri()));
   }
 
   private synchronized Uri getNextUri() {

vito/core-java-impl/src/main/java/com/facebook/fresco/vito/core/impl/ImageSourceToImagePipelineAdapter.kt

@@ -18,6 +18,7 @@ import com.facebook.fresco.urimod.Dimensions
 import com.facebook.fresco.vito.core.ImagePipelineUtils
 import com.facebook.fresco.vito.core.impl.source.DataSourceImageSource
 import com.facebook.fresco.vito.core.impl.source.ImagePipelineImageSource
+import com.facebook.fresco.vito.core.impl.source.RetainingImageSource
 import com.facebook.fresco.vito.options.ImageOptions
 import com.facebook.fresco.vito.source.EmptyImageSource
 import com.facebook.fresco.vito.source.FirstAvailableImageSource
@@ -158,7 +159,24 @@ object ImageSourceToImagePipelineAdapter {
                       extras,
                       viewport)))
 
+      is RetainingImageSource -> {
+        imageSource.setImageSourceUpdateFunction { newImageSource ->
+          createDataSourceSupplier(
+              newImageSource,
+              imagePipeline,
+              imagePipelineUtils,
+              imageOptions,
+              callerContext,
+              requestListener,
+              uiComponentId,
+              extras,
+              viewport)
+        }
+        imageSource.dataSourceSupplier
+      }
+
       is DataSourceImageSource -> imageSource.dataSourceSupplier
+
       else -> NO_REQUEST_SUPPLIER
     }
   }

vito/core-java-impl/src/main/java/com/facebook/fresco/vito/core/impl/source/DataSourceImageSource.kt

@@ -14,6 +14,6 @@ import com.facebook.fresco.vito.source.ImageSource
 import com.facebook.imagepipeline.image.CloseableImage
 
 /** ImageSource that directly supplies a DataSource */
-class DataSourceImageSource(
+open class DataSourceImageSource(
     val dataSourceSupplier: Supplier<DataSource<CloseableReference<CloseableImage>>>
 ) : ImageSource

vito/core-java-impl/src/main/java/com/facebook/fresco/vito/core/impl/source/RetainingImageSource.kt

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.fresco.vito.core.impl.source
+
+import com.facebook.common.internal.Supplier
+import com.facebook.common.references.CloseableReference
+import com.facebook.datasource.DataSource
+import com.facebook.datasource.RetainingDataSourceSupplier
+import com.facebook.fresco.vito.source.ImageSource
+import com.facebook.fresco.vito.source.ImageSourceProvider
+import com.facebook.imagepipeline.image.CloseableImage
+
+/**
+ * Retaining image source. This image source allows to be updated to load a new image but retain the
+ * old image until the new image is available. The image source can be updated by calling
+ * [updateImageSource].
+ */
+class RetainingImageSource(
+    private var currentSource: ImageSource = ImageSourceProvider.emptySource(),
+    val dataSourceSupplier: RetainingDataSourceSupplier<CloseableReference<CloseableImage>> =
+        RetainingDataSourceSupplier(),
+) : ImageSource {
+
+  private var imageSourceUpdateFunction:
+      ((ImageSource) -> Supplier<DataSource<CloseableReference<CloseableImage>>>)? =
+      null
+
+  /**
+   * Update the image to be displayed. Will keep the current image visible until the new one is
+   * available.
+   *
+   * @param imageSource the new image source to be used
+   * @param forceReload to force reloading the image, even if the same image source is already set
+   */
+  @JvmOverloads
+  fun updateImageSource(imageSource: ImageSource, forceReload: Boolean = false) {
+    if (forceReload || currentSource != imageSource) {
+      currentSource = imageSource
+      imageSourceUpdateFunction?.let { dataSourceSupplier.replaceSupplier(it(imageSource)) }
+    }
+  }
+
+  fun setImageSourceUpdateFunction(
+      function: (ImageSource) -> Supplier<DataSource<CloseableReference<CloseableImage>>>
+  ) {
+    imageSourceUpdateFunction = function
+    updateImageSource(currentSource, true)
+  }
+}