Flutter：使用多个参数实例化对象

Question

我在尝试从我的预定义构造函数实例化对象时遇到语法（我猜？）问题。

Category(String kategorieName, Image cover){
  kategorieTitel = kategorieName;
  kategorieCover = cover;
}

我试图创建一个动态列表，稍后将用于在 ListView.builder 中自动填充构造函数。

  List kategorien = [
{
  'name' : 'Location1',
  'pic' : Asset.Image('assets/img/Locations.jpg')
},
{
  'name' : 'Location2',
   ...
}];

自动填充名称工作正常，但我无法使用相应的图像文件调用构造函数。

  child: ListView.builder(
    itemCount: kategorien.length,
    itemBuilder: (context, index){
      return Padding(
        padding: EdgeInsets.all(5.0),
        child: Category('${kategorien[index]['name']}'),

我尝试过像 Category('${kategorien[index]['name']}', '${kategorien[index][pic]}')

这样的连接

我不知道如何通过列表为构造函数提供图像。非常感谢您的帮助！

Answer 1

您可以试试下面的代码：

/// Category needs to be a widget so it can be assigned
/// to the child property of the Padding widget.
class Category extends StatelessWidget {
  final String kategorieName;
  final ImageProvider cover; // AssetImage is part of the ImageProvider interface not Image.

  const Category(this.kategorieName, this.cover);

  // As Category is a widget you will need to override the build method.
  @override
  Widget build(BuildContext context) {
    return Container(
      height: 100, // You can adapt the height depending on your needs
      decoration: BoxDecoration(
        image: DecorationImage(image: cover),
      ),
    );
  }
}

final kategorien = <Map<String, dynamic>>[
  {
    'name': 'Location1',
    'pic': const AssetImage('assets/img/Locations.jpg'), // AssetImage is the correct way of casting your image.
  },
  {
    'name': 'Location2',
    'pic': const AssetImage('assets/img/Locations.jpg'),
  },
];

class MyImages extends StatelessWidget {
  const MyImages({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: kategorien.length,
      itemBuilder: (_, index) {
        final element = kategorien.elementAt(index);
        return Padding(
          padding: const EdgeInsets.all(5.0),
          child: Category(
            '${element['name']}',
            element['pic'] as ImageProvider, // You need to cast the pic field as ImageProvider.
          ),
        );
      },
    );
  }
}

Flutter：使用多个参数实例化对象

Flutter: Instantiate object with multiple parameters

flutter

dart

listview

constructor