最近项目上需要通过MVVM来控制TreeView，其中需要需要控制通过搜索来定位某个节点，正常逻辑下，首先通过需要在树上面找到该节点，然后选中该节点，并将该节点的父节点展开，这个时候需要通过MVVM来控制，需要绑定起来，只是一直没有binding上，代码如下：
MVVM示例代码：
1 using System;
2 using System.Collections.Generic;
3 using System.Collections.ObjectModel;
4 using System.Linq;
5 using System.Text;
6 using System.Threading.Tasks;
7
8 namespace DragDrop
9 {
10 class DataItem : NotifyPropertyBase, ICloneable
11 {
12 public DataItem(string header, int deepth = 1)
13 {
14 Header = header;
15 Deepth = deepth;
16 }
17
18 public object Clone()
19 {
20 DataItem dataItem = new DataItem(Header, Deepth);
21 dataItem.IsExpanded = IsExpanded;
22 dataItem.IsSelected = IsSelected;
23 dataItem.Deepth = Deepth;
24 foreach (DataItem item in Items)
25 dataItem.Items.Add((DataItem)item.Clone());
26 return dataItem;
27 }
28
29 private string header;
30 public string Header
31 {
32 get { return header; }
33 set
34 {
35 SetProperty(ref header, value);
36 }
37 }
38
39 private bool isSelected;
40 public bool IsSelected
41 {
42 get { return isSelected; }
43 set { SetProperty(ref isSelected, value); }
44 }
45
46 private bool isExpanded;
47 public bool IsExpanded
48 {
49 get { return isExpanded; }
50 set
51 {
52 SetProperty(ref isExpanded, value);
53 Console.WriteLine("{0}--{1}", Header, IsExpanded);
54 }
55 }
56
57 private int deepth;
58 public int Deepth
59 {
60 get { return deepth; }
61 set
62 {
63 if (deepth != value)
64 {
65 deepth = value;
66 SetProperty(ref deepth, value);
67 }
68 }
69 }
70
71 private ObservableCollection<DataItem> mItems = null;
72 public ObservableCollection<DataItem> Items
73 {
74 get
75 {
76 if (mItems == null)
77 mItems = new ObservableCollection<DataItem>();
78 return mItems;
79 }
80 }
81
82 }
83
84 class Data
85 {
86 private static Data mInstance = new Data();
87
88 public static Data Instance
89 {
90 get { return mInstance; }
91 }
92
93 private ObservableCollection<DataItem> GenerateTreeViewItems()
94 {
95 ObservableCollection<DataItem> items = new ObservableCollection<DataItem>();
96
97 DataItem item1 = new DataItem("TreeViewItem1");
98 item1.Items.Add(new DataItem("SubItem1", item1.Deepth));
99 item1.Items.Add(new DataItem("SubItem2", item1.Deepth));
100 item1.Items.Add(new DataItem("SubItem3", item1.Deepth));
101 item1.Items.Add(new DataItem("SubItem4", item1.Deepth));
102 items.Add(item1);
103
104 DataItem item2 = new DataItem("TreeViewItem2");
105 item2.Items.Add(new DataItem("SubItem1", item2.Deepth));
106 item2.Items.Add(new DataItem("SubItem2", item2.Deepth));
107 items.Add(item2);
108
109 DataItem item3 = new DataItem("TreeViewItem3");
110 item3.Items.Add(new DataItem("SubItem1", item3.Deepth));
111 item3.Items.Add(new DataItem("SubItem2", item3.Deepth));
112 item3.Items.Add(new DataItem("SubItem3", item3.Deepth));
113 item3.Items.Add(new DataItem("SubItem4", item3.Deepth));
114 item3.Items.Add(new DataItem("SubItem5", item3.Deepth));
115 item3.Items.Add(new DataItem("SubItem6", item3.Deepth));
116 item3.Items.Add(new DataItem("SubItem7", item3.Deepth));
117 item3.Items.Add(new DataItem("SubItem8", item3.Deepth));
118 items.Add(item3);
119
120 return items;
121 }
122
123 private ObservableCollection<DataItem> GenerateListItems()
124 {
125 ObservableCollection<DataItem> items = new ObservableCollection<DataItem>();
126 items.Add(new DataItem("ListBoxItem1"));
127 items.Add(new DataItem("ListBoxItem2"));
128 items.Add(new DataItem("ListBoxItem3"));
129 items.Add(new DataItem("ListBoxItem4"));
130 items.Add(new DataItem("ListBoxItem5"));
131 return items;
132 }
133
134 public ObservableCollection<DataItem> TreeViewItems
135 {
136 get
137 {
138 if (mTreeViewItems == null)
139 mTreeViewItems = GenerateTreeViewItems();
140 return mTreeViewItems;
141 }
142 }
143
144 public ObservableCollection<DataItem> ListBoxItems
145 {
146 get
147 {
148 if (mListBoxItems == null)
149 mListBoxItems = GenerateListItems();
150 return mListBoxItems;
151 }
152 }
153
154 private ObservableCollection<DataItem> mTreeViewItems = null;
155 private ObservableCollection<DataItem> mListBoxItems = null;
156 }
157 }
界面代码：
1 <Window x:Class="DragDrop.MainWindow"
2 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4 xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
5 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
6 xmlns:local="clr-namespace:DragDrop"
7 mc:Ignorable="d"
8 Title="MainWindow" Height="350" Width="525">
9 <Window.Resources>
10 <HierarchicalDataTemplate x:Key="treeViewTemplate" DataType="{x:Type local:DataItem}" ItemsSource="{Binding Items}">
11 <TextBlock Text="{Binding Header}"/>
12 </HierarchicalDataTemplate>
13
14 <Style x:Key="TreeViewStyle" TargetType="{x:Type TreeViewItem}">
15 <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
16 <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
17 <Style.Triggers>
18 <DataTrigger Binding="{Binding Deepth}" Value="1">
19 <Setter Property="IsExpanded" Value="True"/>
20 </DataTrigger>
21 </Style.Triggers>
22 </Style>
23 </Window.Resources>
24 <Grid x:Name="mTopLevelGrid">
25 <TreeView x:Name="mTreeView" Grid.Column="0"
26 ItemsSource="{Binding Source={x:Static local:Data.Instance}, Path=TreeViewItems}"
27 ItemTemplate="{StaticResource treeViewTemplate}"
28 ItemContainerStyle="{StaticResource TreeViewStyle}"/>
29 </Grid>
30 </Window>
数据的绑定没有问题，界面没有问题，奇怪的是IsSelected可以正常绑定，但是IsExpanded就是不行，后来发现这两个属性唯一的区别就是在TreeView的式样中
1 <Style.Triggers>
2 <DataTrigger Binding="{Binding Deepth}" Value="1">
3 <Setter Property="IsExpanded" Value="True"/>
4 </DataTrigger>
5 </Style.Triggers>
后面把这个DataTrigger这段代码注释掉，编译一下，重新运行，IsExpanded就可以正常绑定。后面自己思考了一下，MVVM模式实现将ViewModel与界面上面的显示绑定起来，实际上也就是使用了观察者模式，而Trigger的原理应该和数据binding是一样的，而且这个Trigger写在后面，可能直接把前面的绑定取代了，但是试了一下，将DataTrigger放到前面，也还是绑定不上，这种可能性排除；个人猜测可能是Trigger的优先级比较高，从而造成IsExpanded一直Binding不上去。
原文地址：https://www.cnblogs.com/Johar/p/9886646.html
时间： 2024-08-11 17:28:03