Wpf Backgroundworker

<window x:class="wpfapp53.mainwindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:wpfapp53"
        mc:ignorable="d"
        title="mainwindow" height="450" width="800">
    <grid>
        <grid.rowdefinitions>
            <rowdefinition height="*"/>
            <rowdefinition height="auto"/>
            <rowdefinition height="auto"/>
            <rowdefinition height="auto"/>
        </grid.rowdefinitions>
        <listbox grid.row="0" x:name="listbox1"/>
        <progressbar grid.row="1" x:name="progressbar1" height="20" margin="5"/>
        <stackpanel grid.row="2" orientation="horizontal" margin="5">
            <textblock text="status: "/>
            <textblock x:name="statustextbox"/>
        </stackpanel>
        <grid grid.row="3" margin="10">
            <grid.columndefinitions>
                <columndefinition width="*"/>
                <columndefinition width="*"/>
            </grid.columndefinitions>
            <button grid.column="0" x:name="startbtn" content="start" click="startbtn_click"/>
            <button grid.column="1" x:name="cancelbtn" content="cancel" click="cancelbtn_click"/>
        </grid>
    </grid>
</window>

 1 using system;
 2 using system.collections.generic;
 3 using system.componentmodel;
 4 using system.linq;
 5 using system.text;
 6 using system.threading;
 7 using system.threading.tasks;
 8 using system.windows;
 9 using system.windows.controls;
10 using system.windows.data;
11 using system.windows.documents;
12 using system.windows.input;
13 using system.windows.media;
14 using system.windows.media.imaging;
15 using system.windows.navigation;
16 using system.windows.shapes;
17 
18 namespace wpfapp53
19 {
20     /// <summary>
21     /// interaction logic for mainwindow.xaml
22     /// </summary>
23     public partial class mainwindow : window
24     {
25         backgroundworker bgworker;
26         public mainwindow()
27         {
28             initializecomponent();
29             cancelbtn.isenabled = false;
30         }
31 
32         private void startbtn_click(object sender, routedeventargs e)
33         {
34             listbox1.items.clear();
35             startbtn.isenabled = false;
36             cancelbtn.isenabled = true;
37             bgworker = new backgroundworker();
38             bgworker.dowork += bgworker_dowork;
39             bgworker.progresschanged += bgworker_progresschanged;
40             bgworker.runworkercompleted += bgworker_runworkercompleted;
41             bgworker.workerreportsprogress = true;
42             bgworker.workersupportscancellation = true;
43 
44             int maxitems = 50;
45             progressbar1.minimum = 1;
46             progressbar1.maximum = 100;
47 
48             statustextbox.text = "starting...";
49             bgworker.runworkerasync(maxitems);
50         }
51 
52         private void bgworker_runworkercompleted(object sender, runworkercompletedeventargs e)
53         {
54              if(e.cancelled)
55             {
56                 statustextbox.text = "cancelled";
57             }
58             else
59             {
60                 statustextbox.text = "completed";
61             }
62             statustextbox.isenabled = true;
63             cancelbtn.isenabled = false;
64         }
65 
66         private void bgworker_progresschanged(object sender, progresschangedeventargs e)
67         {
68             double percent = (e.progresspercentage * 100) / 50;
69             progressbar1.value = math.round(percent, 0);
70             listbox1.items.add(new listboxitem { content = e.progresspercentage + " item added" });
71             statustextbox.text = math.round(percent, 0) + "% percent completed";
72         }
73 
74         private void bgworker_dowork(object sender, doworkeventargs e)
75         {
76             int? maxitems = e.argument as int?;
77             for(int i=1;i<=maxitems.getvalueordefault();i++)
78             {
79                 if(bgworker.cancellationpending)
80                 {
81                     e.cancel = true;
82                     break;
83                 }
84                 thread.sleep(200);
85                 bgworker.reportprogress(i);
86             }
87         }
88 
89         private void cancelbtn_click(object sender, routedeventargs e)
90         {
91             bgworker.cancelasync();
92             startbtn.isenabled = true;
93         }
94     }
95 }