flutter - 如何在 flutter 中为下拉弹出窗口设置动态高度

Question

我是 Flutter 开发的新手。我正在使用我的应用程序的下拉按钮。打开下拉菜单时，弹出对话框中的文本被剪切。下面我附上了带有编码的屏幕截图。请指导我解决此问题。

DropdownButtonHideUnderline(
    child: new DropdownButton(
        isExpanded: true,
        value: dropDownValue,
        isDense: true,
        //icon: Icon(Icons.keyboard_arrow_down, color: Colors.white,),
        onChanged: (String newValue) {
            setState(() {
                dropDownValue = newValue;    
                state.didChange(newValue);
            });
        },
        items: dropDownList.map((String value) {
            return new DropdownMenuItem(
                value: value,
                child: new SizedBox(
                width: MediaQuery.of(context).size.width / 1.4,
                child: new Text(value,
                    softWrap: true,
                    style: TextStyle(color: Colors.white, fontSize: 18.0),),)
                );
            }).toList(),
        ),
    ),
);

Answer 1

复制DropdownMenuItem其他人建议的类(class)还不够DropdownButton需要 items为 List<DropdownMenuItem<T>> 类型.

我创建了以下小部件，应该可以帮助您解决问题:

import 'package:flutter/material.dart';

/// Looks like a DropdownButton but has a few differences:
///
/// 1. Can be opened by a single tap even if the keyboard is showing (this might be a bug of the DropdownButton)
///
/// 2. The width of the overlay can be different than the width of the child
///
/// 3. The current selection is highlighted in the overlay
class CustomDropdown<T> extends PopupMenuButton<T> {
  CustomDropdown({
    Key key,
    @required PopupMenuItemBuilder<T> itemBuilder,
    @required T selectedValue,
    PopupMenuItemSelected<T> onSelected,
    PopupMenuCanceled onCanceled,
    String tooltip,
    double elevation = 8.0,
    EdgeInsetsGeometry padding = const EdgeInsets.all(8.0),
    Icon icon,
    Offset offset = Offset.zero,
    Widget child,
    String placeholder = "Please select",
  }) : super(
    key: key,
    itemBuilder: itemBuilder,
    initialValue: selectedValue,
    onSelected: onSelected,
    onCanceled: onCanceled,
    tooltip: tooltip,
    elevation: elevation,
    padding: padding,
    icon: icon,
    offset: offset,
    child: child == null ? null : Stack(
      children: <Widget>[
        Builder(
          builder: (BuildContext context) => Container(
            height: 48,
            alignment: AlignmentDirectional.centerStart,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                DefaultTextStyle(
                  style: selectedValue!= null ? Theme.of(context).textTheme.subhead
                      : Theme.of(context).textTheme.subhead.copyWith(color:     
Theme.of(context).hintColor),
                  child: Expanded(child: selectedValue== null ? Text(placeholder) : child),
                ),
                IconTheme(
                  data: IconThemeData(
                    color: Theme.of(context).brightness == Brightness.light
                        ? Colors.grey.shade700 : Colors.white70,
                  ),
                  child: const Icon(Icons.arrow_drop_down),
                ),
              ],
            ),
          ),
        ),
        Positioned(
          left: 0.0,
          right: 0.0,
          bottom: 8,
          child: Container(
            height: 1,
            decoration: const BoxDecoration(
              border: Border(bottom: BorderSide(color: Color(0xFFBDBDBD), width: 0.0)),
            ),
          ),
        ),
      ],
    ),
  );
}

它实际上扩展了 PopupMenuButton如您所见，但我使它看起来与 DropdownButton 相同.

itemBuilder需要返回List<PopupMenuEntry<T>> , 每个条目通常是 PopupMenuItem您可以向其提供任何child小部件。

selectedValue是当前选定的值，将在叠加层中突出显示。如果为空，则为 Text带有 placeholder 的小部件显示字符串。如果不为空，child小部件已显示。

你应该能够通过修改这个类来禁用高亮，或者调用 super()与 initialValue null，或者更好的方法是在构造函数中添加一个 bool 值来从外部控制它。