方法'findRenderObject‘被调用为null

Question

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _sTabController;
  List<GlobalKey> keyList = <GlobalKey>[];

  @override
  void initState() {
    keyList.clear();
    _sTabController = ScrollController();
    WidgetsBinding.instance.addPostFrameCallback((_) {
      readyOfWidget();
    });
    for (int i = 0; i < 25; i++) {
      keyList.add(GlobalKey(debugLabel: 'item_$i'));
    }
    super.initState();
  }

  void readyOfWidget() {
    for (int i = 0; i < keyList.length; i++) {
        RenderBox tabKeyItemRenderBox =
        keyList[i].currentContext.findRenderObject();
        if (tabKeyItemRenderBox != null) {
          Offset positionOfRenderBox =
          tabKeyItemRenderBox.localToGlobal(Offset.zero);
          print('keyItemRenderBox dx {$i}: ${positionOfRenderBox.dx}');
        }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        // height: 60,
        child: ListView(
          controller: _sTabController,
          shrinkWrap: true,
          scrollDirection: Axis.horizontal,
          children: List.generate(keyList.length, (index) {
            return Wrap(
              children: [
                Container(
                  key: keyList.elementAt(index),
                  color: index % 2 == 0 ? Colors.red : Colors.green,
                  child: Padding(
                      padding: EdgeInsets.only(top: 10,bottom: 10,left: 40,right: 40),
                      child: Text(
                        'Text $index',
                        style: TextStyle(fontSize: 21),
                      )),
                )
              ],
            );
          }),
        ),
      ),
    );
  }
}

输出

I/颤振( 5864)：keyItemRenderBox dx {0}：0.0

I/颤振( 5864)：keyItemRenderBox dx {1}：77.0

I/颤振( 5864)：keyItemRenderBox dx {2}：154.0

I/颤振( 5864)：keyItemRenderBox dx {3}：231.0

I/颤振( 5864)：keyItemRenderBox dx {4}：308.0

I/颤振( 5864)：keyItemRenderBox dx {5}：385.0

I/颤振( 5864)：keyItemRenderBox dx {6}：462.0

I/颤振( 5864)：keyItemRenderBox dx {7}：539.0

I/颤振( 5864)：keyItemRenderBox dx {8}：616.0

调度程序库═════════════════════════════════════════════════════捕获的════════异常

方法'findRenderObject‘被调用为null。

接收器:空

尝试调用: findRenderObject()

════════════════════════════════════════════════════════════════════════════════════════════════════

也是当你试着用下面的方法

padding: EdgeInsets.only(top: 10,bottom: 10,left: 40,right: 40),

输出

I/颤振( 7007)：keyItemRenderBox dx {0}：0.0

I/颤振( 7007)：keyItemRenderBox dx {1}：137.0

I/颤振( 7007)：keyItemRenderBox dx {2}：274.0

I/颤振( 7007)：keyItemRenderBox dx {3}：411.0

I/颤振( 7007)：keyItemRenderBox dx {4}：548.0

调度程序库═════════════════════════════════════════════════════捕获的════════异常

方法'findRenderObject‘被调用为null。

接收器:空

尝试调用: findRenderObject()

════════════════════════════════════════════════════════════════════════════════════════════════════

是否有可能获取所有水平列表项的findRenderObject()？

Answer 1

之所以发生这种情况，是因为尚未呈现项目(第9项)。ListView执行延迟呈现。

因此，如果您想要实现这一点，您需要您的"SingleChildScrollView“与轴线为"Axis.horizontal”。