Add an experimental plugin system for decorating OnPreDrawListener in Glide.

library/src/main/java/com/bumptech/glide/GlidePlugins.java

@@ -0,0 +1,39 @@
+package com.bumptech.glide;
+
+import android.view.ViewTreeObserver.OnPreDrawListener;
+import java.util.function.Function;
+
+/**
+ * A class for holding static methods that are used to globally modify the behavior of Glide. This
+ * class is used to allow apps to globally modify the behavior of Glide.
+ */
+public final class GlidePlugins {
+
+  private static Function<OnPreDrawListener, OnPreDrawListener> onPreDrawListenerDecorator = null;
+
+  /**
+   * Sets a decorator to be applied to all {@link OnPreDrawListener}s created by Glide.
+   *
+   * <p>This is intended to be used by apps that want to globally modify all {@link
+   * OnPreDrawListener}s created by Glide.
+   *
+   * <p>This is an experimental method that may be removed without warning in a future version.
+   */
+  public static void experimentalSetOnPreDrawListenerDecorator(
+      Function<OnPreDrawListener, OnPreDrawListener> decorator) {
+    onPreDrawListenerDecorator = decorator;
+  }
+
+  /**
+   * Returns the {@link OnPreDrawListener} provided, possibly after being decorated by {@link
+   * #experimentalSetOnPreDrawListenerDecorator(Function)}.
+   */
+  public static OnPreDrawListener decorateOnPreDrawListener(OnPreDrawListener listener) {
+    if (onPreDrawListenerDecorator == null) {
+      return listener;
+    }
+    return onPreDrawListenerDecorator.apply(listener);
+  }
+
+  private GlidePlugins() {}
+}

library/src/main/java/com/bumptech/glide/request/target/CustomViewTarget.java

@@ -14,6 +14,7 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
+import com.bumptech.glide.GlidePlugins;
 import com.bumptech.glide.R;
 import com.bumptech.glide.request.Request;
 import com.bumptech.glide.request.transition.Transition;
@@ -299,7 +300,7 @@ static final class SizeDeterminer {
     private final List<SizeReadyCallback> cbs = new ArrayList<>();
     @Synthetic boolean waitForLayout;
 
-    @Nullable private SizeDeterminerLayoutListener layoutListener;
+    @Nullable private ViewTreeObserver.OnPreDrawListener layoutListener;
 
     SizeDeterminer(@NonNull View view) {
       this.view = view;
@@ -359,7 +360,8 @@ void getSize(@NonNull SizeReadyCallback cb) {
       }
       if (layoutListener == null) {
         ViewTreeObserver observer = view.getViewTreeObserver();
-        layoutListener = new SizeDeterminerLayoutListener(this);
+        layoutListener =
+            GlidePlugins.decorateOnPreDrawListener(new SizeDeterminerLayoutListener(this));
         observer.addOnPreDrawListener(layoutListener);
       }
     }

library/src/main/java/com/bumptech/glide/request/target/ViewTarget.java

@@ -14,6 +14,7 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
+import com.bumptech.glide.GlidePlugins;
 import com.bumptech.glide.R;
 import com.bumptech.glide.request.Request;
 import com.bumptech.glide.util.Preconditions;
@@ -324,7 +325,7 @@ static final class SizeDeterminer {
     private final List<SizeReadyCallback> cbs = new ArrayList<>();
     @Synthetic boolean waitForLayout;
 
-    @Nullable private SizeDeterminerLayoutListener layoutListener;
+    @Nullable private ViewTreeObserver.OnPreDrawListener layoutListener;
 
     SizeDeterminer(@NonNull View view) {
       this.view = view;
@@ -384,7 +385,8 @@ void getSize(@NonNull SizeReadyCallback cb) {
       }
       if (layoutListener == null) {
         ViewTreeObserver observer = view.getViewTreeObserver();
-        layoutListener = new SizeDeterminerLayoutListener(this);
+        layoutListener =
+            GlidePlugins.decorateOnPreDrawListener(new SizeDeterminerLayoutListener(this));
         observer.addOnPreDrawListener(layoutListener);
       }
     }

library/src/test/java/com/bumptech/glide/request/target/CustomViewTargetTest.java

@@ -3,6 +3,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.inOrder;
@@ -20,14 +21,17 @@
 import android.view.ViewGroup;
 import android.view.ViewGroup.LayoutParams;
 import android.view.ViewTreeObserver;
+import android.view.ViewTreeObserver.OnPreDrawListener;
 import android.widget.FrameLayout;
 import android.widget.LinearLayout;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import com.bumptech.glide.GlidePlugins;
 import com.bumptech.glide.request.Request;
 import com.bumptech.glide.request.transition.Transition;
 import com.google.common.truth.Truth;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Function;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -56,6 +60,7 @@ public class CustomViewTargetTest {
   private CustomViewTarget<View, Object> target;
   @Mock private SizeReadyCallback cb;
   @Mock private Request request;
+  @Mock private Function<OnPreDrawListener, OnPreDrawListener> onPreDrawListenerDecorator;
   private AttachStateTarget attachStateTarget;
 
   @Before
@@ -84,6 +89,7 @@ public void setUp() {
   @After
   public void tearDown() {
     CustomViewTarget.SizeDeterminer.maxDisplayLength = null;
+    GlidePlugins.experimentalSetOnPreDrawListenerDecorator(null);
   }
 
   @Test
@@ -591,6 +597,17 @@ public void onLoadStarted_withoutClearOnDetach_doesNotAddListener() {
     verify(request, never()).clear();
   }
 
+  @Test
+  public void getSize_whenPreDrawListenerIsUsed_appliesDecorator() {
+    when(onPreDrawListenerDecorator.apply(any(OnPreDrawListener.class)))
+        .thenAnswer(invocation -> invocation.getArgument(0));
+    GlidePlugins.experimentalSetOnPreDrawListenerDecorator(onPreDrawListenerDecorator);
+
+    target.getSize(cb);
+
+    verify(onPreDrawListenerDecorator).apply(any(OnPreDrawListener.class));
+  }
+
   @Test
   public void onLoadCleared_withoutClearOnDetach_doesNotRemoveListeners() {
     final AtomicInteger count = new AtomicInteger();

library/test/src/test/java/com/bumptech/glide/request/target/ViewTargetTest.java

@@ -4,6 +4,7 @@
 import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.inOrder;
@@ -26,6 +27,7 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.test.core.app.ApplicationProvider;
+import com.bumptech.glide.GlidePlugins;
 import com.bumptech.glide.request.Request;
 import com.bumptech.glide.request.transition.Transition;
 import com.bumptech.glide.tests.Util;
@@ -34,6 +36,7 @@
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.function.Function;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -64,6 +67,7 @@ public class ViewTargetTest {
   private PreDrawShadowViewTreeObserver shadowObserver;
   @Mock private SizeReadyCallback cb;
   @Mock private Request request;
+  @Mock private Function<OnPreDrawListener, OnPreDrawListener> onPreDrawListenerDecorator;
   private int sdkVersion;
   private AttachStateTarget attachStateTarget;
 
@@ -83,6 +87,7 @@ public void setUp() {
   public void tearDown() {
     Util.setSdkVersionInt(sdkVersion);
     ViewTarget.SizeDeterminer.maxDisplayLength = null;
+    GlidePlugins.experimentalSetOnPreDrawListenerDecorator(null);
   }
 
   @Test
@@ -441,6 +446,17 @@ public void getSize_withWidthAndHeightEqualToPadding_doesNotCallSizeReady() {
     verify(cb, never()).onSizeReady(anyInt(), anyInt());
   }
 
+  @Test
+  public void getSize_whenPreDrawListenerIsUsed_appliesDecorator() {
+    when(onPreDrawListenerDecorator.apply(any(OnPreDrawListener.class)))
+        .thenAnswer(invocation -> invocation.getArgument(0));
+    GlidePlugins.experimentalSetOnPreDrawListenerDecorator(onPreDrawListenerDecorator);
+
+    target.getSize(cb);
+
+    verify(onPreDrawListenerDecorator).apply(any(OnPreDrawListener.class));
+  }
+
   private void setDisplayDimens(Integer width, Integer height) {
     WindowManager windowManager =
         (WindowManager)