更新loading

lib/dialog/loading/loading.dart

@@ -6,8 +6,7 @@ class Loading {
   static LoadingDialog _dialog;
   static BuildContext _context;
 
-  static Future show(
-    BuildContext context, {
+  static Future show(BuildContext context, {
     String msg,
   }) async {
     dismiss();
@@ -24,7 +23,9 @@ class Loading {
 
   static dismiss() {
     if (_dialog != null && _context != null) {
-      Navigator.pop(_context);
+      if (Navigator.canPop(_context)) {
+        Navigator.pop(_context);
+      }
     }
     _context = null;
     _dialog = null;