Fix.

Yuncong Zhang · Yuncong Zhang · commit 39bd903279d6 · 2019-10-12T17:06:23.000+08:00
diff --git a/Runtime/widgets/automatic_keep_alive.cs b/Runtime/widgets/automatic_keep_alive.cs
@@ -81,6 +81,7 @@ bool _addClient(KeepAliveNotification notification) {
         }
 
         ParentDataElement _getChildElement() {
+            D.assert(this.mounted);
             Element element = (Element) this.context;
             Element childElement = null;
             element.visitChildren((Element child) => { childElement = child; });

Original file line number	Diff line number	Diff line change
`@@ -81,6 +81,7 @@ bool _addClient(KeepAliveNotification notification) {`
`81`	`81`	`}`
`82`	`82`
`83`	`83`	`ParentDataElement _getChildElement() {`
	`84`	`+ D.assert(this.mounted);`
`84`	`85`	`Element element = (Element) this.context;`
`85`	`86`	`Element childElement = null;`
`86`	`87`	`element.visitChildren((Element child) => { childElement = child; });`