WPF TreeView IsExpanded 绑定不上的问题

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。