Python/Kivy中RecycleView如何正确设置列表默认选中项

你遇到的状态冲突来自Kivy RecycleView 选中逻辑的两层设计不匹配：

• 你自定义存放在rv.data里的selected字段是独立的业务标记
• SelectableRecycleBoxLayout继承的LayoutSelectionBehavior自己维护了一套内部选中节点索引，初始化时这套索引是空的。视图第一次渲染时，apply_selection会把所有项的is_selected参数传为False，直接覆盖你在refresh_view_attrs里预设的选中状态，这就是默认选中不生效的根源。
  你注释掉self.selected = is_selected后虽然能显示默认选中，但后续用户点击操作是修改内部选中索引的，没有同步到视图属性，所以交互会完全失效。

不需要改动原有点击交互逻辑，只要做两处调整，把默认选中状态同步到布局的内部选中索引，同时做好数据源和视图的状态同步即可：

1. 在apply_selection中同步选中状态回rv.data，避免滚动复用时状态错乱
2. 等RecycleView布局初始化完成后，批量把预设选中的索引用布局自带的select_node方法加入内部选中集合，和用户点击触发的选中逻辑完全对齐。

修正后的完整代码 #

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.recycleview import RecycleView
from kivy.uix.recycleview.views import RecycleDataViewBehavior
from kivy.uix.label import Label
from kivy.properties import BooleanProperty
from kivy.uix.recycleboxlayout import RecycleBoxLayout
from kivy.uix.behaviors import FocusBehavior
from kivy.uix.recycleview.layout import LayoutSelectionBehavior
from kivy.clock import Clock

Builder.load_string('''
<SelectableLabel>:
    # Draw a background to indicate selection
    canvas.before:
        Color:
            rgba: (.0, 0.9, .1, .3) if self.selected else (0, 0, 0, 1)
        Rectangle:
            pos: self.pos
            size: self.size
<RV>:
    viewclass: 'SelectableLabel'
    SelectableRecycleBoxLayout:
        default_size: None, dp(56)
        default_size_hint: 1, None
        size_hint_y: None
        height: self.minimum_height
        orientation: 'vertical'
        multiselect: True
        touch_multiselect: True
''')

class SelectableRecycleBoxLayout(FocusBehavior, LayoutSelectionBehavior,
                                 RecycleBoxLayout):
    ''' Adds selection and focus behaviour to the view. '''

class SelectableLabel(RecycleDataViewBehavior, Label):
    ''' Add selection support to the Label '''
    index = None
    selected = BooleanProperty(False)
    selectable = BooleanProperty(True)

    def refresh_view_attrs(self, rv, index, data):
        ''' Catch and handle the view changes '''
        self.index = index
        return super(SelectableLabel, self).refresh_view_attrs(
            rv, index, data)

    def on_touch_down(self, touch):
        ''' Add selection on touch down '''
        if super(SelectableLabel, self).on_touch_down(touch):
            return True
        if self.collide_point(*touch.pos) and self.selectable:
            return self.parent.select_with_touch(self.index, touch)

    def apply_selection(self, rv, index, is_selected):
        ''' Respond to the selection of items in the view. '''
        self.selected = is_selected
        # 同步状态到数据源，避免滚动复用视图时选中状态错位
        rv.data[index]['selected'] = is_selected
        if is_selected:
            print("selection changed to {0}".format(rv.data[index]))
        else:
            print("selection removed for {0}".format(rv.data[index]))

class RV(RecycleView):
    def __init__(self, items, **kwargs):
        if 'selection' in kwargs:
            selection = kwargs['selection']
            del kwargs['selection']
        else:
            selection = [False]*len(items)
        super().__init__(**kwargs)
        self.data = [{'text': x, 'selected': selection[i]} \
            for i, x in enumerate(items)]
        # 保存需要默认选中的索引，等布局初始化完成后同步
        self._default_selected_idx = [i for i, val in enumerate(selection) if val]
        Clock.schedule_once(self._sync_default_selection, 0)

    def _sync_default_selection(self, dt):
        # 获取内部选择布局实例
        select_layout = self.children[0]
        for idx in self._default_selected_idx:
            # 调用布局原生选中方法，和点击触发逻辑完全一致
            select_layout.select_node(idx)

items = [
    "apple", "dog", "banana", "cat", "pear", "rat", 
    "pineapple", "bat", "pizza", "ostrich",
    "apple", "dog", "banana", "cat", "pear", "rat", 
    "pineapple", "bat", "pizza", "ostrich",
]

class TestApp(App):
    def build(self):
        return RV(items, 
            selection=[x[0] in ['p','a','r'] \
            for x in items]
        )

if __name__ == '__main__':
    test_app = TestApp()
    test_app.run()

关键说明 #

• 删掉了refresh_view_attrs里手动设置self.selected的逻辑，选中状态统一由apply_selection接管，避免两个方法同时修改状态产生冲突
• 用Clock.schedule_once延迟一帧执行默认选中同步，是因为RV初始化时内部的SelectableRecycleBoxLayout还没完成挂载，直接调用选中方法会找不到节点报错
• 所有选中状态修改都走布局原生的select_node逻辑，默认选中和用户手动选中的行为完全一致，不会出现状态不同步的问题，滚动列表时也不会出现选中状态错位。

内容的提问来源于stack exchange，提问作者iperetta