App Widget Tree

# App Widget Tree

App
└── ContactsProvider
    └── MaterialApp
        └── {Routes}
            ├── HomeScreen
            │   └── Scaffold
            │       ├── AppBar
            │       ├── ListView
            │       │   └── ContactListItem
            │       └── FloatingActionButton
            └── AddContactScreen
                └── Scaffold
                    ├── AppBar
                    └── Form
                        ├── WordFormField
                        └── DatePickerField

Flutter Container MaxWidth.md

Flutter Container MaxWidth

Container(
constraints: BoxConstraints(maxWidth:200)
...
)

screen width.md

Get Screen Width

使用MediaQuery查询

 MediaQuery.of(context).size.width * 0.4