Import a copy of ItemTouchHelper

Based on RecyclerView 1.2.1

settings.gradle

@@ -13,6 +13,7 @@ include ':app:autodiscovery:srvrecords'
 include ':app:autodiscovery:thunderbird'
 include ':app:html-cleaner'
 include ':ui-utils:LinearLayoutManager'
+include ':ui-utils:ItemTouchHelper'
 include ':mail:common'
 include ':mail:testing'
 include ':mail:protocols:imap'

ui-utils/ItemTouchHelper/build.gradle

@@ -0,0 +1,27 @@
+apply plugin: 'com.android.library'
+
+dependencies {
+    api "androidx.recyclerview:recyclerview:${versions.androidxRecyclerView}"
+}
+
+android {
+    namespace 'app.k9mail.ui.utils.itemtouchhelper'
+
+    compileSdkVersion buildConfig.compileSdk
+    buildToolsVersion buildConfig.buildTools
+
+    defaultConfig {
+        minSdkVersion buildConfig.minSdk
+        targetSdkVersion buildConfig.robolectricSdk
+    }
+
+    lintOptions {
+        abortOnError false
+        lintConfig file("$rootProject.projectDir/config/lint/lint.xml")
+    }
+
+    compileOptions {
+        sourceCompatibility javaVersion
+        targetCompatibility javaVersion
+    }
+}

ui-utils/ItemTouchHelper/src/main/java/app/k9mail/ui/utils/itemtouchhelper/ItemTouchUIUtilImpl.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2018 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 app.k9mail.ui.utils.itemtouchhelper;
+
+import android.graphics.Canvas;
+import android.os.Build;
+import android.view.View;
+
+import androidx.core.view.ViewCompat;
+import androidx.recyclerview.R;
+import androidx.recyclerview.widget.ItemTouchUIUtil;
+import androidx.recyclerview.widget.RecyclerView;
+
+
+/**
+ * Package private class to keep implementations. Putting them inside ItemTouchUIUtil makes them
+ * public API, which is not desired in this case.
+ */
+class ItemTouchUIUtilImpl implements ItemTouchUIUtil {
+    static final ItemTouchUIUtil INSTANCE =  new ItemTouchUIUtilImpl();
+
+    @Override
+    public void onDraw(Canvas c, RecyclerView recyclerView, View view, float dX, float dY,
+            int actionState, boolean isCurrentlyActive) {
+        if (Build.VERSION.SDK_INT >= 21) {
+            if (isCurrentlyActive) {
+                Object originalElevation = view.getTag(R.id.item_touch_helper_previous_elevation);
+                if (originalElevation == null) {
+                    originalElevation = ViewCompat.getElevation(view);
+                    float newElevation = 1f + findMaxElevation(recyclerView, view);
+                    ViewCompat.setElevation(view, newElevation);
+                    view.setTag(R.id.item_touch_helper_previous_elevation, originalElevation);
+                }
+            }
+        }
+
+        view.setTranslationX(dX);
+        view.setTranslationY(dY);
+    }
+
+    private static float findMaxElevation(RecyclerView recyclerView, View itemView) {
+        final int childCount = recyclerView.getChildCount();
+        float max = 0;
+        for (int i = 0; i < childCount; i++) {
+            final View child = recyclerView.getChildAt(i);
+            if (child == itemView) {
+                continue;
+            }
+            final float elevation = ViewCompat.getElevation(child);
+            if (elevation > max) {
+                max = elevation;
+            }
+        }
+        return max;
+    }
+
+    @Override
+    public void onDrawOver(Canvas c, RecyclerView recyclerView, View view, float dX, float dY,
+            int actionState, boolean isCurrentlyActive) {
+    }
+
+    @Override
+    public void clearView(View view) {
+        if (Build.VERSION.SDK_INT >= 21) {
+            final Object tag = view.getTag(R.id.item_touch_helper_previous_elevation);
+            if (tag instanceof Float) {
+                ViewCompat.setElevation(view, (Float) tag);
+            }
+            view.setTag(R.id.item_touch_helper_previous_elevation, null);
+        }
+
+        view.setTranslationX(0f);
+        view.setTranslationY(0f);
+    }
+
+    @Override
+    public void onSelected(View view) {
+    }
+}