Only clear all if value changes. (#7212)

If we remove all when the innerHTML
value stays the same we will loose the innerHTML
on the client as the value is not re-sent,
but is still cleared from the client.

Fixes #4644

(cherry picked from commit efdc44a)

flow-server/src/main/java/com/vaadin/flow/dom/Element.java

@@ -19,6 +19,7 @@
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.function.Predicate;
@@ -722,7 +723,12 @@ private Element setRawProperty(String name, Serializable value) {
         verifySetPropertyName(name);
 
         if ("innerHTML".equals(name)) {
-            removeAllChildren();
+            Serializable oldValue = getStateProvider()
+                    .getProperty(getNode(), name);
+            if(!Objects.equals(value, oldValue)) {
+                // Only remove all children for value change
+                removeAllChildren();
+            }
         }
         getStateProvider().setProperty(getNode(), name, value, true);
 

flow-tests/test-root-context/src/main/java/com/vaadin/flow/uitest/ui/ElementInnerHtmlView.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2000-2019 Vaadin Ltd.
+ *
+ * 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 com.vaadin.flow.uitest.ui;
+
+import com.vaadin.flow.component.html.Div;
+import com.vaadin.flow.component.html.NativeButton;
+import com.vaadin.flow.router.Route;
+import com.vaadin.flow.uitest.servlet.ViewTestLayout;
+
+@Route(value = "com.vaadin.flow.uitest.ui.ElementInnerHtmlView", layout = ViewTestLayout.class)
+public class ElementInnerHtmlView extends AbstractDivView {
+
+    Div innerHtml;
+
+    @Override
+    protected void onShow() {
+        innerHtml = new Div();
+        innerHtml.setId("inner-html-field");
+        add(createButton("Foo"), createButton("Boo"), getNullButton(),
+                innerHtml);
+
+    }
+
+    private NativeButton createButton(String value) {
+        NativeButton button = new NativeButton("Set value " + value,
+                click -> innerHtml.getElement().setProperty("innerHTML",
+                        String.format("<p>%s</p>", value)));
+        button.setId("set-" + value.toLowerCase());
+        return button;
+    }
+
+    private NativeButton getNullButton() {
+        NativeButton button = new NativeButton("Set value null",
+                click -> innerHtml.getElement().setProperty("innerHTML", null));
+        button.setId("set-null");
+        return button;
+    }
+
+}

flow-tests/test-root-context/src/test/java/com/vaadin/flow/uitest/ui/ElementInnerHtmlIT.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2000-2019 Vaadin Ltd.
+ *
+ * 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 com.vaadin.flow.uitest.ui;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.vaadin.flow.component.html.testbench.DivElement;
+import com.vaadin.flow.component.html.testbench.NativeButtonElement;
+import com.vaadin.flow.testutil.ChromeBrowserTest;
+
+public class ElementInnerHtmlIT extends ChromeBrowserTest {
+
+    @Test
+    public void elementInitOrder() {
+        open();
+        DivElement innerHtml = $(DivElement.class).id("inner-html-field");
+
+        Assert.assertEquals("", innerHtml.getPropertyString("innerHTML"));
+
+        $(NativeButtonElement.class).id("set-foo").click();
+        Assert.assertEquals("<p>Foo</p>", innerHtml.getPropertyString("innerHTML"));
+
+        $(NativeButtonElement.class).id("set-foo").click();
+        Assert.assertEquals("<p>Foo</p>", innerHtml.getPropertyString("innerHTML"));
+
+        $(NativeButtonElement.class).id("set-boo").click();
+        Assert.assertEquals("<p>Boo</p>", innerHtml.getPropertyString("innerHTML"));
+
+        $(NativeButtonElement.class).id("set-boo").click();
+        Assert.assertEquals("<p>Boo</p>", innerHtml.getPropertyString("innerHTML"));
+
+        $(NativeButtonElement.class).id("set-null").click();
+        Assert.assertEquals("", innerHtml.getPropertyString("innerHTML"));
+
+    }
+}