我是飞翼开发的新手。我正在使用我的应用程序的下拉按钮。打开下拉菜单时，文本将在弹出对话框中被剪切。下面我附上了一个截图与编码。请指导我解决这个问题。

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(),
        ),
    ),
);

按照其他人的建议复制DropdownMenuItem类是不够的，因为DropdownButton要求items的类型为List<DropdownMenuItem<T>>。
我创建了以下小部件，可以帮助解决您的问题：

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，但我使它看起来与DropdownButton相同。
itemBuilder需要返回List<PopupMenuEntry<T>>，每个条目通常是一个PopupMenuItem，您可以向其提供任何child小部件。
selectedValue是当前选择的值，将在覆盖图中突出显示。如果为null，则显示带有placeholder字符串的Text小部件。如果不为空，则显示child小部件。
您应该能够通过修改这个类来禁用突出显示，要么调用super()，initialValue为null，要么更好地向构造函数添加一个布尔值，以便从外部控制它。

3条答案

按热度按时间

1hdlvixo1#

赞(0）回复(0）举报 2023-05-19

mum43rcc2#

DropdownMenuItem的高度被硬编码为_kMenuItemHeight：
https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/material/dropdown.dart#L486
您唯一能做的就是复制整个文件并根据需要进行调整。

blpfk2vs3#

只需将DropdownButton的itemHeight属性设置为null，项目就具有动态高度。

DropdownButton(
      ... 
      itemHeight: null, 
      ...
    )

文档链接：https://api.flutter.dev/flutter/material/DropdownButton/itemHeight.html

flutter中如何设置下拉弹出的动态高度

3条答案

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