以编程方式在Flutter上显示/隐藏小部件

Question

在Android上,每个View子类都有一个"setVisibility"方法,允许您修改View对象的可见性

设置可见性有3个选项:

• visibile:在布局中呈现视图可见
• 不可见:隐藏视图,但留下的间隙等于视图在可见时占用的间隔
• 消失:隐藏视图,并将其从布局中完全删除.好像它的高度和宽度都是0dp

Flutter中的Widgets是否有与上述相同的东西？

有关快速参考:https://developer.android.com/reference/android/view/View.html#attr_android : visibility

Answer 1

不可见:窗口小部件占用屏幕上的物理空间,但对用户不可见.

走了:小部件不占用任何物理空间而已完全消失.

更新

Flutter添加了一个名为的新Widget if

隐形的例子

Visibility(
  child: Text("Invisible"),
  maintainSize: true, 
  maintainAnimation: true,
  maintainState: true,
  visible: false, 
),

举个例子

Visibility(
  child: Text("Gone"),
  visible: false,
),

旧解决方案

Column(
  children: <Widget>[
    if (show) Text("This can be visible/not depending on condition"),
    Text("This is always visible"),
  ],
) 

Answer 2

与问题协作并显示用空替换它的示例Container().

这是以下示例:

import "package:flutter/material.dart";

void main() {
  runApp(new ControlleApp());
}

class ControlleApp extends StatelessWidget { 
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: "My App",
      home: new HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  HomePageState createState() => new HomePageState();
}

class HomePageState extends State<HomePage> {
  bool visibilityTag = false;
  bool visibilityObs = false;

  void _changed(bool visibility, String field) {
    setState(() {
      if (field == "tag"){
        visibilityTag = visibility;
      }
      if (field == "obs"){
        visibilityObs = visibility;
      }
    });
  }

  @override
  Widget build(BuildContext context){
    return new Scaffold(
      appBar: new AppBar(backgroundColor: new Color(0xFF26C6DA)),
      body: new ListView(
        children: <Widget>[
          new Container(
            margin: new EdgeInsets.all(20.0),
            child: new FlutterLogo(size: 100.0, colors: Colors.blue),
          ),
          new Container(
            margin: new EdgeInsets.only(left: 16.0, right: 16.0),
            child: new Column(
              children: <Widget>[
                visibilityObs ? new Row(
                  crossAxisAlignment: CrossAxisAlignment.end,
                  children: <Widget>[
                    new Expanded(
                      flex: 11,
                      child: new TextField(
                        maxLines: 1,
                        style: Theme.of(context).textTheme.title,
                        decoration: new InputDecoration(
                          labelText: "Observation",
                          isDense: true
                        ),
                      ),
                    ),
                    new Expanded(
                      flex: 1,
                      child: new IconButton(
                        color: Colors.grey[400],
                        icon: const Icon(Icons.cancel, size: 22.0,),
                        onPressed: () {
                          _changed(false, "obs");
                        },
                      ),
                    ),
                  ],
                ) : new Container(),

                visibilityTag ? new Row(
                  crossAxisAlignment: CrossAxisAlignment.end,
                  children: <Widget>[
                    new Expanded(
                      flex: 11,
                      child: new TextField(
                        maxLines: 1,
                        style: Theme.of(context).textTheme.title,
                        decoration: new InputDecoration(
                          labelText: "Tags",
                          isDense: true
                        ),
                      ),
                    ),
                    new Expanded(
                      flex: 1,
                      child: new IconButton(
                        color: Colors.grey[400],
                        icon: const Icon(Icons.cancel, size: 22.0,),
                        onPressed: () {
                          _changed(false, "tag");
                        },
                      ),
                    ),
                  ],
                ) : new Container(),
              ],
            )
          ),
          new Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              new InkWell(
                onTap: () {
                  visibilityObs ? null : _changed(true, "obs");
                },
                child: new Container(
                  margin: new EdgeInsets.only(top: 16.0),
                  child: new Column(
                    children: <Widget>[
                      new Icon(Icons.comment, color: visibilityObs ? Colors.grey[400] : Colors.grey[600]),
                      new Container(
                        margin: const EdgeInsets.only(top: 8.0),
                        child: new Text(
                          "Observation",
                          style: new TextStyle(
                            fontSize: 12.0,
                            fontWeight: FontWeight.w400,
                            color: visibilityObs ? Colors.grey[400] : Colors.grey[600],
                          ),
                        ),
                      ),
                    ],
                  ),
                )
              ),
              new SizedBox(width: 24.0),
              new InkWell(
                onTap: () {
                  visibilityTag ? null : _changed(true, "tag");
                },
                child: new Container(
                  margin: new EdgeInsets.only(top: 16.0),
                  child: new Column(
                    children: <Widget>[
                      new Icon(Icons.local_offer, color: visibilityTag ? Colors.grey[400] : Colors.grey[600]),
                      new Container(
                        margin: const EdgeInsets.only(top: 8.0),
                        child: new Text(
                          "Tags",
                          style: new TextStyle(
                            fontSize: 12.0,
                            fontWeight: FontWeight.w400,
                            color: visibilityTag ? Colors.grey[400] : Colors.grey[600],
                          ),
                        ),
                      ),
                    ],
                  ),
                )
              ),
            ],
          )                    
        ],
      )
    );
  }
}

Answer 3

你可以用Visibility与Opacity的opacity:画使元素隐藏,但仍然占据空间.

为了使其不占空间,请将其更换为空0.0.

编辑:要将其包装在Opacity对象中,请执行以下操作:

            new Opacity(opacity: 0.0, child: new Padding(
              padding: const EdgeInsets.only(
                left: 16.0,
              ),
              child: new Icon(pencil, color: CupertinoColors.activeBlue),
            ))

Google Developers关于Opacity的快速教程:https://youtu.be/9hltevOHQBw

Answer 4

尝试Offstage小部件

如果属性offstage:true不占据物理空间并且不可见，

如果属性offstage:false将占用物理空间并且可见

Offstage(
   offstage: true,
   child: Text("Visible"),
),

Answer 5

Flutter现在包含一个“ 可见性”小部件，您应该使用它来显示/隐藏小部件。通过更改替换，该小部件还可用于在2个小部件之间切换。

这个小部件可以实现任何可见，不可见，消失等状态。

    Visibility(
      visible: true //Default is true,
      child: Text('Ndini uya uya'),
      //maintainSize: bool. When true this is equivalent to invisible;
      //replacement: Widget. Defaults to Sizedbox.shrink, 0x0
    ),

Answer 6

您可以使用名为 (Visibility) 的新小部件在代码中封装任何小部件，这是来自小部件最左侧的黄色灯，您希望它不可见

示例：假设您想让一行不可见：

1. 单击灯并选择（Wrap with widget）
2. 将小部件重命名为可见性
3. 添加可见属性并将其设置为false

4. 新创建的小部件（可见性小部件）的子部件是您希望它不可见的小部件

             Visibility(
                 visible: false,
                 child: Row(
                   crossAxisAlignment: CrossAxisAlignment.start,
                   children: <Widget>[
                     SizedBox(
                       width: 10,
                     ),
                     Text("Search",
                       style: TextStyle(fontSize: 20
                       ),),
                   ],
                 ),
               ),
   

我希望它会在未来帮助某人

Answer 7

bool _visible = false;

 void _toggle() {
    setState(() {
      _visible = !_visible;
    });
  }

onPressed: _toggle,

Visibility(
            visible:_visible,
            child: new Container(
            child: new  Container(
              padding: EdgeInsets.fromLTRB(15.0, 0.0, 15.0, 10.0),
              child: new Material(
                elevation: 10.0,
                borderRadius: BorderRadius.circular(25.0),
                child: new ListTile(
                  leading: new Icon(Icons.search),
                  title: new TextField(
                    controller: controller,
                    decoration: new InputDecoration(
                        hintText: 'Search for brands and products', border: InputBorder.none,),
                    onChanged: onSearchTextChanged,
                  ),
                  trailing: new IconButton(icon: new Icon(Icons.cancel), onPressed: () {
                    controller.clear();
                    onSearchTextChanged('');
                  },),
                ),
              ),
            ),
          ),
          ),

Answer 8

更新

Flutter 现在有一个可见性小部件。要实现您自己的解决方案，请从以下代码开始。

自己制作一个小部件。

显示隐藏

class ShowWhen extends StatelessWidget {
  final Widget child;
  final bool condition;
  ShowWhen({this.child, this.condition});

  @override
  Widget build(BuildContext context) {
    return Opacity(opacity: this.condition ? 1.0 : 0.0, child: this.child);
  }
}

显示/删除

class RenderWhen extends StatelessWidget {
  final Widget child;
  final bool condition;
  RenderWhen({this.child, this.show});

  @override
  Widget build(BuildContext context) {
    return this.condition ? this.child : Container();
  }
}

顺便说一句，有没有人对上面的小部件有更好的名称？

更多阅读

1. 文章如何使可视性部件。

Answer 9

在flutter 1.5和Dart 2.3 中，可见性消失了，您可以通过在集合中使用 if 语句来设置可见性，而无需使用容器。

例如

child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
              Text('This is text one'),
              if (_isVisible) Text('can be hidden or shown'), // no dummy container/ternary needed
              Text('This is another text'),
              RaisedButton(child: Text('show/hide'), onPressed: (){
                  setState(() {
                    _isVisible = !_isVisible; 
                  });
              },)

          ],
        )

Answer 10

初学者也可以试试这个。

class Visibility extends StatefulWidget {
  @override
  _VisibilityState createState() => _VisibilityState();
}

class _VisibilityState extends State<Visibility> {
  bool a = true;
  String mText = "Press to hide";

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: "Visibility",
      home: new Scaffold(
          body: new Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              new RaisedButton(
                onPressed: _visibilitymethod, child: new Text(mText),),
                a == true ? new Container(
                width: 300.0,
                height: 300.0,
                color: Colors.red,
              ) : new Container(),
            ],
          )
      ),
    );
  }

  void _visibilitymethod() {
    setState(() {
      if (a) {
        a = false;
        mText = "Press to show";
      } else {
        a = true;
        mText = "Press to hide";
      }
    });
  }
}

Answer 11

正如@CopsOnRoad 已经强调的那样，您可以使用可见性小部件。但是，如果你想保持它的状态，例如，如果你想建立一个viewpager，让某个按钮基于页面出现和消失，你可以这样做

void checkVisibilityButton() {
  setState(() {
  isVisibileNextBtn = indexPage + 1 < pages.length;
  });
}    

 Stack(children: <Widget>[
      PageView.builder(
        itemCount: pages.length,
        onPageChanged: (index) {
          indexPage = index;
          checkVisibilityButton();
        },
        itemBuilder: (context, index) {
          return pages[index];
        },
        controller: controller,
      ),
      Container(
        alignment: Alignment.bottomCenter,
        child: Row(
          mainAxisAlignment: MainAxisAlignment.end,
          children: <Widget>[
            Visibility(
              visible: isVisibileNextBtn,
              child: "your widget"
            )
          ],
        ),
      )
    ]))

Answer 12

恕我直言，如果您不需要显示小部件，则 Flutter 中不需要可见性属性或特殊小部件，只需不要将其添加到小部件树或将其替换为空小部件：

  @override
  Widget build(BuildContext context) {
    return someFlag ? Text('Here I am') : SizedBox();
  }

我认为 Visibility 小部件存在的原因是因为很多人问:) 人们习惯于通过某些属性控制元素的可见性