show gifs in CaptionDialog (#4536)

closes #4528

app/src/main/java/com/keylesspalace/tusky/components/compose/dialog/CaptionDialog.kt

@@ -16,6 +16,7 @@
 package com.keylesspalace.tusky.components.compose.dialog
 
 import android.content.Context
+import android.graphics.drawable.Animatable
 import android.graphics.drawable.Drawable
 import android.net.Uri
 import android.os.Bundle
@@ -45,6 +46,8 @@ class CaptionDialog : DialogFragment() {
 
     private val binding by viewBinding(DialogImageDescriptionBinding::bind)
 
+    private var animatable: Animatable? = null
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setStyle(STYLE_NORMAL, R.style.TuskyDialogFragmentStyle)
@@ -97,6 +100,23 @@ class CaptionDialog : DialogFragment() {
                     resource: Drawable,
                     transition: Transition<in Drawable>?
                 ) {
+                    if (resource is Animatable) {
+                        resource.callback = object : Drawable.Callback {
+                            override fun invalidateDrawable(who: Drawable) {
+                                view.invalidate()
+                            }
+
+                            override fun scheduleDrawable(who: Drawable, what: Runnable, `when`: Long) {
+                                view.postDelayed(what, `when`)
+                            }
+
+                            override fun unscheduleDrawable(who: Drawable, what: Runnable) {
+                                view.removeCallbacks(what)
+                            }
+                        }
+                        resource.start()
+                        animatable = resource
+                    }
                     imageView.setImageDrawable(resource)
                 }
 
@@ -128,6 +148,12 @@ class CaptionDialog : DialogFragment() {
         listener = context as? Listener ?: error("Activity is not ComposeCaptionDialog.Listener")
     }
 
+    override fun onDestroyView() {
+        super.onDestroyView()
+        animatable?.stop()
+        (animatable as? Drawable?)?.callback = null
+    }
+
     interface Listener {
         fun onUpdateDescription(localId: Int, description: String)
     }