appcompat/appcompat/src/main/java/androidx/appcompat/app/ResourcesFlusher.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License
 */

package androidx.appcompat.app;

import android.content.res.Resources;
import android.os.Build;
import android.util.Log;
import android.util.LongSparseArray;

import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;

import java.lang.reflect.Field;
import java.util.Map;

class ResourcesFlusher {
    private static final String TAG = "ResourcesFlusher";

    private static Field sDrawableCacheField;
    private static boolean sDrawableCacheFieldFetched;

    private static Class<?> sThemedResourceCacheClazz;
    private static boolean sThemedResourceCacheClazzFetched;

    private static Field sThemedResourceCache_mUnthemedEntriesField;
    private static boolean sThemedResourceCache_mUnthemedEntriesFieldFetched;

    private static Field sResourcesImplField;
    private static boolean sResourcesImplFieldFetched;

    static void flush(@NonNull final Resources resources) {
        if (Build.VERSION.SDK_INT >= 28) {
            // no-op on P and above
            return;
        } else if (Build.VERSION.SDK_INT >= 24) {
            flushNougats(resources);
        } else if (Build.VERSION.SDK_INT >= 23) {
            flushMarshmallows(resources);
        } else if (Build.VERSION.SDK_INT >= 21) {
            flushLollipops(resources);
        }
    }

    @RequiresApi(21)
    private static void flushLollipops(@NonNull final Resources resources) {
        if (!sDrawableCacheFieldFetched) {
            try {
                sDrawableCacheField = Resources.class.getDeclaredField("mDrawableCache");
                sDrawableCacheField.setAccessible(true);
            } catch (NoSuchFieldException e) {
                Log.e(TAG, "Could not retrieve Resources#mDrawableCache field", e);
            }
            sDrawableCacheFieldFetched = true;
        }
        if (sDrawableCacheField != null) {
            Map drawableCache = null;
            try {
                drawableCache = (Map) sDrawableCacheField.get(resources);
            } catch (IllegalAccessException e) {
                Log.e(TAG, "Could not retrieve value from Resources#mDrawableCache", e);
            }
            if (drawableCache != null) {
                drawableCache.clear();
            }
        }
    }

    @RequiresApi(23)
    private static void flushMarshmallows(@NonNull final Resources resources) {
        if (!sDrawableCacheFieldFetched) {
            try {
                sDrawableCacheField = Resources.class.getDeclaredField("mDrawableCache");
                sDrawableCacheField.setAccessible(true);
            } catch (NoSuchFieldException e) {
                Log.e(TAG, "Could not retrieve Resources#mDrawableCache field", e);
            }
            sDrawableCacheFieldFetched = true;
        }

        Object drawableCache = null;
        if (sDrawableCacheField != null) {
            try {
                drawableCache = sDrawableCacheField.get(resources);
            } catch (IllegalAccessException e) {
                Log.e(TAG, "Could not retrieve value from Resources#mDrawableCache", e);
            }
        }

        if (drawableCache == null) {
            // If there is no drawable cache, there's nothing to flush...
            return;
        }

        flushThemedResourcesCache(drawableCache);
    }

    @RequiresApi(24)
    private static void flushNougats(@NonNull final Resources resources) {
        if (!sResourcesImplFieldFetched) {
            try {
                sResourcesImplField = Resources.class.getDeclaredField("mResourcesImpl");
                sResourcesImplField.setAccessible(true);
            } catch (NoSuchFieldException e) {
                Log.e(TAG, "Could not retrieve Resources#mResourcesImpl field", e);
            }
            sResourcesImplFieldFetched = true;
        }

        if (sResourcesImplField == null) {
            // If the mResourcesImpl field isn't available, bail out now
            return;
        }

        Object resourcesImpl = null;
        try {
            resourcesImpl = sResourcesImplField.get(resources);
        } catch (IllegalAccessException e) {
            Log.e(TAG, "Could not retrieve value from Resources#mResourcesImpl", e);
        }

        if (resourcesImpl == null) {
            // If there is no impl instance, bail out now
            return;
        }

        if (!sDrawableCacheFieldFetched) {
            try {
                sDrawableCacheField = resourcesImpl.getClass().getDeclaredField("mDrawableCache");
                sDrawableCacheField.setAccessible(true);
            } catch (NoSuchFieldException e) {
                Log.e(TAG, "Could not retrieve ResourcesImpl#mDrawableCache field", e);
            }
            sDrawableCacheFieldFetched = true;
        }

        Object drawableCache = null;
        if (sDrawableCacheField != null) {
            try {
                drawableCache = sDrawableCacheField.get(resourcesImpl);
            } catch (IllegalAccessException e) {
                Log.e(TAG, "Could not retrieve value from ResourcesImpl#mDrawableCache", e);
            }
        }

        if (drawableCache != null) {
            flushThemedResourcesCache(drawableCache);
        }
    }

    @RequiresApi(16)
    private static void flushThemedResourcesCache(@NonNull final Object cache) {
        if (!sThemedResourceCacheClazzFetched) {
            try {
                sThemedResourceCacheClazz = Class.forName("android.content.res.ThemedResourceCache");
            } catch (ClassNotFoundException e) {
                Log.e(TAG, "Could not find ThemedResourceCache class", e);
            }
            sThemedResourceCacheClazzFetched = true;
        }

        if (sThemedResourceCacheClazz == null) {
            // If the ThemedResourceCache class isn't available, bail out now
            return;
        }

        if (!sThemedResourceCache_mUnthemedEntriesFieldFetched) {
            try {
                sThemedResourceCache_mUnthemedEntriesField =
                        sThemedResourceCacheClazz.getDeclaredField("mUnthemedEntries");
                sThemedResourceCache_mUnthemedEntriesField.setAccessible(true);
            } catch (NoSuchFieldException ee) {
                Log.e(TAG, "Could not retrieve ThemedResourceCache#mUnthemedEntries field", ee);
            }
            sThemedResourceCache_mUnthemedEntriesFieldFetched = true;
        }

        if (sThemedResourceCache_mUnthemedEntriesField == null) {
            // Didn't get mUnthemedEntries field, bail out...
            return;
        }

        LongSparseArray unthemedEntries = null;
        try {
            unthemedEntries = (LongSparseArray)
                    sThemedResourceCache_mUnthemedEntriesField.get(cache);
        } catch (IllegalAccessException e) {
            Log.e(TAG, "Could not retrieve value from ThemedResourceCache#mUnthemedEntries", e);
        }

        if (unthemedEntries != null) {
            unthemedEntries.clear();
        }
    }

    private ResourcesFlusher() {
    }
}