add one example:tap button refresh replace pull down refresh(#282)

example/lib/ui/example/ExamplePage.dart

@@ -23,6 +23,7 @@ import 'package:example/ui/example/useStage/twolevel_refresh.dart';
 import 'useStage/qq_chat_list.dart';
 import 'otherwidget/refresh_recordable_listview_example.dart';
 import 'otherwidget/draggable_bottomsheet_loadmore.dart';
+import 'useStage/tapbutton_refresh.dart';
 
 class ExamplePage extends StatefulWidget {
   @override
@@ -107,6 +108,13 @@ class _ExamplePageState extends State<ExamplePage>
               );
             }));
           }),
+      ExampleItem(
+          title: "点击按钮触发刷新",
+          onClick: () {
+            Navigator.of(context).push(MaterialPageRoute(builder: (context) {
+              return TapButtonRefreshExample();
+            }));
+          }),
       ExampleItem(
           title: "NestedScrollView下刷新",
           onClick: () {

example/lib/ui/example/useStage/tapbutton_refresh.dart

@@ -0,0 +1,125 @@
+/*
+ * Author: Jpeng
+ * Email: [email protected]
+ * Time:  2020-06-21 13:43
+ */
+
+import 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+import 'package:pull_to_refresh/pull_to_refresh.dart';
+
+/*
+    achieve requirement
+    tap button to trigger refresh insteal of pull down refresh
+ */
+class TapButtonRefreshExample extends StatefulWidget {
+  TapButtonRefreshExample();
+
+  @override
+  State<StatefulWidget> createState() {
+    // TODO: implement createState
+    return _TapButtonRefreshExampleState();
+  }
+}
+
+class _TapButtonRefreshExampleState extends State<TapButtonRefreshExample> {
+  List<String> data = [];
+  RefreshController _refreshController =
+  RefreshController(initialRefresh: false);
+  bool _enablePullDown = false;
+
+
+  Widget buildEmpty() {
+    // there are two ways
+    // this way is more converient,but it doesn't reference ListView some attribute
+    // If you don't need some attribute like physics,cacheExtent,just default
+    // you can return emptyWidget directly,else return ListView
+    // from 1.5.2,you needn't  compute the height by LayoutBuilder,If your boxConstaints is double.infite,
+    // SmartRefresher can convert the height to the viewport mainExtent
+    return Column(
+      mainAxisAlignment: MainAxisAlignment.center,
+      children: <Widget>[
+        Image.asset(
+          "images/empty1.png",
+          fit: BoxFit.cover,
+        ),
+        Text("没数据,请点击按钮刷新")
+      ],
+    );
+    // second way
+    return ListView(
+      children: [
+        Image.asset(
+          "images/empty.png",
+          fit: BoxFit.cover,
+        )
+      ],
+      physics: BouncingScrollPhysics(),
+      cacheExtent: 100.0,
+    );
+  }
+
+  @override
+  void initState() {
+    // TODO: implement initState
+    super.initState();
+    _refreshController.headerMode.addListener(() {
+      if(_refreshController.headerMode.value == RefreshStatus.idle){
+
+        Future.delayed(const Duration(milliseconds: 20)).then((value)  {
+        _enablePullDown = false;
+            setState(() {
+
+        });
+        });
+      }
+    });
+  }
+
+
+  @override
+  Widget build(BuildContext context) {
+    // TODO: implement build
+    return Scaffold(
+      body: SmartRefresher(
+        controller: _refreshController,
+        enablePullUp: data.length != 0,
+        enablePullDown: _enablePullDown,
+        header: ClassicHeader(),
+        onRefresh: () async {
+          await Future.delayed(const Duration(milliseconds: 2000));
+          if (mounted)
+            setState(() {
+              data.add("new");
+              data.add("new");
+              data.add("new");
+              data.add("new");
+              data.add("new");
+              data.add("new");
+            });
+          _refreshController.refreshCompleted();
+        },
+        child: data.length == 0
+            ? buildEmpty()
+            : ListView.builder(
+          itemBuilder: (c, i) => Text(data[i]),
+          itemCount: data.length,
+          itemExtent: 100.0,
+        ),
+      ),
+      appBar: AppBar(
+        title: Text("点击按钮刷新"),
+        actions: [GestureDetector(
+          onTap: (){
+            _enablePullDown = true;
+            setState(() {
+
+            });
+            WidgetsBinding.instance.addPostFrameCallback((timeStamp) { _refreshController.requestRefresh();});
+          },
+          child: Icon(Icons.refresh),
+        )],
+      ),
+    );
+  }
+}