Add placeholder drawable for asyncDrawableLoader

markwon-core/src/main/java/ru/noties/markwon/image/AsyncDrawable.java

@@ -39,6 +39,26 @@ public class AsyncDrawable extends Drawable {
         this.loader = loader;
         this.imageSizeResolver = imageSizeResolver;
         this.imageSize = imageSize;
+
+        final Drawable placeholder = loader.placeholder();
+        if (placeholder != null) {
+
+            // process placeholder bounds
+            final Rect bounds = placeholder.getBounds();
+            if (bounds.isEmpty()) {
+                // set intrinsic bounds
+                final Rect rect = new Rect(
+                        0,
+                        0,
+                        placeholder.getIntrinsicWidth(),
+                        placeholder.getIntrinsicHeight());
+                placeholder.setBounds(rect);
+                setBounds(rect);
+            }
+
+            // apply placeholder immediately if we have one
+            setResult(placeholder);
+        }
     }
 
     @NonNull
@@ -66,6 +86,15 @@ public class AsyncDrawable extends Drawable {
 
         // if not null -> means we are attached
         if (callback != null) {
+
+            // as we have a placeholder now, it's important to check it our placeholder
+            // has a proper callback at this point. This is not required in most cases,
+            // as placeholder should be static, but if it's not -> it can operate as usual
+            if (result != null
+                    && result.getCallback() == null) {
+                result.setCallback(callback);
+            }
+
             loader.load(destination, this);
         } else {
             if (result != null) {

markwon-core/src/main/java/ru/noties/markwon/image/AsyncDrawableLoader.java

@@ -12,6 +12,14 @@ import java.util.concurrent.Executors;
 
 public abstract class AsyncDrawableLoader {
 
+    /**
+     * @since 3.0.0
+     */
+    public interface DrawableProvider {
+        @Nullable
+        Drawable provide();
+    }
+
     /**
      * @since 3.0.0
      */
@@ -33,6 +41,8 @@ public abstract class AsyncDrawableLoader {
 
     public abstract void cancel(@NonNull String destination);
 
+    @Nullable
+    public abstract Drawable placeholder();
 
     public static class Builder {
 
@@ -40,7 +50,8 @@ public abstract class AsyncDrawableLoader {
         final Map<String, SchemeHandler> schemeHandlers = new HashMap<>(3);
         final Map<String, MediaDecoder> mediaDecoders = new HashMap<>(3);
         MediaDecoder defaultMediaDecoder;
-        Drawable errorDrawable;
+        DrawableProvider placeholderDrawableProvider;
+        DrawableProvider errorDrawableProvider;
 
         @NonNull
         public Builder executorService(@NonNull ExecutorService executorService) {
@@ -94,9 +105,21 @@ public abstract class AsyncDrawableLoader {
             return this;
         }
 
+        /**
+         * @since 3.0.0
+         */
         @NonNull
-        public Builder errorDrawable(Drawable errorDrawable) {
-            this.errorDrawable = errorDrawable;
+        public Builder placeholderDrawableProvider(@NonNull DrawableProvider placeholderDrawableProvider) {
+            this.placeholderDrawableProvider = placeholderDrawableProvider;
+            return this;
+        }
+
+        /**
+         * @since 3.0.0
+         */
+        @NonNull
+        public Builder errorDrawableProvider(@NonNull DrawableProvider errorDrawableProvider) {
+            this.errorDrawableProvider = errorDrawableProvider;
             return this;
         }
 

markwon-core/src/main/java/ru/noties/markwon/image/AsyncDrawableLoaderImpl.java

@@ -5,6 +5,7 @@ import android.net.Uri;
 import android.os.Handler;
 import android.os.Looper;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -20,7 +21,8 @@ class AsyncDrawableLoaderImpl extends AsyncDrawableLoader {
     private final Map<String, SchemeHandler> schemeHandlers;
     private final Map<String, MediaDecoder> mediaDecoders;
     private final MediaDecoder defaultMediaDecoder;
-    private final Drawable errorDrawable;
+    private final DrawableProvider placeholderDrawableProvider;
+    private final DrawableProvider errorDrawableProvider;
 
     private final Handler mainThread;
 
@@ -31,7 +33,8 @@ class AsyncDrawableLoaderImpl extends AsyncDrawableLoader {
         this.schemeHandlers = builder.schemeHandlers;
         this.mediaDecoders = builder.mediaDecoders;
         this.defaultMediaDecoder = builder.defaultMediaDecoder;
-        this.errorDrawable = builder.errorDrawable;
+        this.placeholderDrawableProvider = builder.placeholderDrawableProvider;
+        this.errorDrawableProvider = builder.errorDrawableProvider;
         this.mainThread = new Handler(Looper.getMainLooper());
     }
 
@@ -49,6 +52,14 @@ class AsyncDrawableLoaderImpl extends AsyncDrawableLoader {
         }
     }
 
+    @Nullable
+    @Override
+    public Drawable placeholder() {
+        return placeholderDrawableProvider != null
+                ? placeholderDrawableProvider.provide()
+                : null;
+    }
+
     private Future<?> execute(@NonNull final String destination, @NonNull AsyncDrawable drawable) {
 
         final WeakReference<AsyncDrawable> reference = new WeakReference<AsyncDrawable>(drawable);
@@ -109,7 +120,9 @@ class AsyncDrawableLoaderImpl extends AsyncDrawableLoader {
 
                 // if result is null, we assume it's an error
                 if (result == null) {
-                    result = errorDrawable;
+                    result = errorDrawableProvider != null
+                            ? errorDrawableProvider.provide()
+                            : null;
                 }
 
                 if (result != null) {

markwon-core/src/main/java/ru/noties/markwon/image/AsyncDrawableLoaderNoOp.java

@@ -1,6 +1,8 @@
 package ru.noties.markwon.image;
 
+import android.graphics.drawable.Drawable;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 class AsyncDrawableLoaderNoOp extends AsyncDrawableLoader {
     @Override
@@ -12,4 +14,10 @@ class AsyncDrawableLoaderNoOp extends AsyncDrawableLoader {
     public void cancel(@NonNull String destination) {
 
     }
+
+    @Nullable
+    @Override
+    public Drawable placeholder() {
+        return null;
+    }
 }