Flutter学习笔记之-基础Widget的简单使用

Flutter学习笔记之-基础Widget的简单使用

• 文本Text Widget

Text分为文本和富文本展示

普通文本

class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text(
      'Hello, ssssadfasdfdsfdsfasdfdfdasdfadsfadfadfdfdfdfdfdfdfdfdfdfdfafdss! How are you?',
      textAlign: TextAlign.left,
      overflow: TextOverflow.ellipsis, // 超出区域显示...
      style: TextStyle(fontWeight: FontWeight.bold),
      maxLines: 2,
    );
  }
}

富文本

class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text.rich(
        TextSpan(
          text: "hello",
          children: [
            TextSpan(text: "测试", style: TextStyle(color: Colors.red)),
            TextSpan(text: "富文本", style: TextStyle(color: Colors.green, fontSize: 20))
          ]
        )
    );
  }
}

• Image图片

flutter的图片支持JPEG, PNG, GIF, Animated GIF, WebP, Animated WebP, BMP, and WBMP格式。

Image接受一个ImageProvider的参数，ImageProvider是一个抽象类，ImageProvider的实现子类有：NetworkImage、AssetImage、FileImage、MemoryImage等

// 加载网络图片
class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Image(
      image: NetworkImage(
        "https://dss3.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=2534506313,1688529724&fm=26&gp=0.jpg"
      ),
    );
  }
}

class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Image.network("https://dss3.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=2534506313,1688529724&fm=26&gp=0.jpg");
  }
}

AssetImage 本地图片使用配置：
1、项目目录中创建images文件夹
2、在pubspec.yaml配置文件中打开图片配置

assets:
      - images/test.jpg
      // 多尺寸配置@2x、@3x配置
      - images/2x/test.jpg
      - images/3x/test.jpg
      // 引入某一个文件夹下所有图片配置
      - images/2x/

3、点击package get添加依赖
4、在代码中使用

class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Image.asset("images/test.jpg");
  }
}

占位图的实现

class _DemoFulWidgetState extends State {
  @override
  Widget build(BuildContext context) {
    return FadeInImage(
      fadeOutDuration: Duration(milliseconds: 1),
      fadeInDuration: Duration(milliseconds: 1),
      placeholder: AssetImage("images/test.jpg"),
      image: NetworkImage("https://dss1.bdstatic.com/70cFvXSh_Q1YnxGkpoWK1HF6hhy/it/u=1636778189,1177027796&fm=26&gp=0.jpg"),
    );
  }
}

• 按钮Widget

class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        // 有阴影的button
        RaisedButton(child: Text("RaisedButton"), textColor: Colors.white, color: Colors.black),

        FlatButton(child: Text("FlatButton"), color: Colors.red),
        // 圆角button
        FloatingActionButton(child: Text("圆角")),
        // 图标button
        IconButton(icon: Icon(Icons.favorite)),
        // 带边框的button
        OutlineButton(child: Text("OutlineButton")),
        // 自定义button
        RaisedButton(
          child: Text("同意协议", style: TextStyle(color: Colors.white)),
          color: Colors.orange, // 按钮的颜色
          highlightColor: Colors.orange[700], // 按下去高亮颜色
          shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(20)), // 圆角的实现
          onPressed: () {
            print("同意协议");
          },
        ),
        // 带点击效果
        InkWell(child: Text("InkWell"), onTap: () {
          print("InkWell");
        },),
        // 下拉选择框的button
        DropdownButton(items: [
          DropdownMenuItem(child: Text("DropdownMenuItem1"), value: "DropdownMenuItem1"),
          DropdownMenuItem(child: Text("DropdownMenuItem2"), value: "DropdownMenuItem2")
        ], onChanged: (String value) {
          print("value = $value");
        }, value: "DropdownMenuItem1"),
      ],
    );
  }
}

• Icon Widget

提供一些默认的Icon图标，没有交互效果

class DemoWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Icon(
            Icons.favorite, 
            size: 210, 
            color: Colors.red, 
            // 不会展示在UI上
            semanticLabel: "test"
        )
      ],
    );
  }
}

• TextField

点击按钮如何获取输入框的值的案例

class DemoFulWidget extends StatefulWidget {
  @override
  _DemoFulWidgetState createState() => _DemoFulWidgetState();
}

class _DemoFulWidgetState extends State {

  TextEditingController _controller;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _controller = TextEditingController();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Container(
          margin: EdgeInsets.all(10),
          child: TextField(
            controller: _controller,
            obscureText: true,
            decoration: InputDecoration(
                border: OutlineInputBorder(),
//              border: InputBorder.none,
                labelText: "password",
                icon: Icon(Icons.lock),
                // placeholder
                hintText: "请输入密码"
            ),
            onChanged: (value) {
              print("onChanged - $value");
            },
            onSubmitted: (value) {
              print("onSubmitted - $value");
            },
          ),
        ),
        Container(
          margin: EdgeInsets.all(10),
          width: double.infinity,
          decoration: BoxDecoration(
              borderRadius: BorderRadius.circular(10),
            color: Colors.red
          ),
          child: FlatButton(
              child: Text("提交"),
            onPressed: () {
                print("获取TextFile的值：value = ${_controller.text}");
            },
          ),
        )
      ],
    );
  }
}