如何为Flutter中的下拉菜单设置动态高度 [英] How to set dynamic height for dropdown popup in flutter

问题描述

我是扑扑发展的新手.我正在使用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.下面我附上了带有编码的屏幕截图.请指导我解决此问题.

I am new to flutter development. I am using the dropdown button of my application. When opening the drop-down menu, the text is getting cut in the popup dialog. Below I attached a screenshot with coding. Please guide me in fixing this issue.

                 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(),
                  ),
                ),);

推荐答案

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>>.

Copying the DropdownMenuItem class as someone else suggested will not be enough as DropdownButton requires items to be of type List<DropdownMenuItem<T>>.

我创建了以下小部件，该小部件应该可以帮助您解决问题:

I have created the following widget which should help with your issue:

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)),
            ),
          ),
        ),
      ],
    ),
  );
}

正如您所看到的，它实际上扩展了PopupMenuButton，但是我使它看起来与DropdownButton相同.

It actually extends PopupMenuButton as you can see, but I've made it look the same as the DropdownButton.

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.

itemBuilder needs to return List<PopupMenuEntry<T>>, with each entry usually being a PopupMenuItem to which you can provide any child widget.

selectedValue是当前选择的值，它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null，则会显示child小部件.

selectedValue is the currently selected value, which will be highlighted in the overlay. If it is null, a Text widget with the placeholder string is shown. If it is not null, the child widget is shown.

通过修改此类以使用initialValue为null的方式调用super()，或者最好在构造函数中添加一个布尔值以从外部进行控制，您应该能够禁用突出显示.

You should be able to disable the highlight by modifying this class to either call super() with an initialValue of null, or even better add a boolean to the constructor to control this from the outside.

这篇关于如何为Flutter中的下拉菜单设置动态高度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！