使用WPF构建应用程序时，想要保证系统的流畅性、用户的体验性，处理好UI线程（主线程）与其他线程（子线程）的关系是必要的。
以最近大火的直播带货为例，镜头前主播（部分副播）的语言动作是主线程，镜头外的场控、客服等人员，各自都有一个属于自己的子线程。场控在做软硬件调试、商品上架下架、发优惠信息，临时更改产品价格、数据监测，客服处理已经出单，物流，复购，销售统计等等操作，这些不可能都交给主播来做，不然时不时的冷场就太尴尬了。要让场控、客服等在镜头外做好辅助工作，并适时的把需要展示的信息传递给主播，才能保证直播的质量。
回归代码本身，要处理线程问题，一般使用Dispatcher和BackgroundWorker来处理子线程与主线程的交互。
1、Dispatcher使用
新建一个简单的WPF项目、只放置一个Button和一个TextBlock，点击Button，使用子线程修改TextBlock的值
<StackPanel VerticalAlignment="Center" Orientation="Horizontal">
<Button
Margin="10,0"
Click="Button_Click"
Content="变更" />
<TextBlock
Name="txt"
VerticalAlignment="Center"
Text="1" />
</StackPanel>
private void Button_Click(object sender, RoutedEventArgs e)
{
Thread thread = new Thread(UpdateText);
thread.Start();
}
private void UpdateText()
{
Thread.Sleep(TimeSpan.FromSeconds(1));
//1、直接修改，报错：System.InvalidOperationException:“调用线程无法访问此对象，因为另一个线程拥有该对象。”
//this.txt.Text = "New text";
//2、使用Dispatcher，把子线程的方法，丢回给主线程执行。
Dispatcher.BeginInvoke(new Action(() =>
{
this.txt.Text = "New text";
}));
}
明显 Dispatcher的使用，把子线程中需要操作主线程的部分，丢回给了主线程，这样完美结果了更改报错的问题。但这种写法不适合在其方法内部处理耗时任务，同时过多的使用Thread来处理异步方法，也会带来不易管理、处理共享数据加锁等问题。
处理简单逻辑是可以使用Dispatcher，处理较为耗时、可能牵扯共享数据或者为方便的管理子线程的启动、停止等，微软提供了BackgroundWorker组件，来安全的处理这些问题。
2、BackgroundWorker的使用
下面代码实现了一个查找指定范围整数范围内的所有素数的功能，XAML代码如下：
<Grid Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<TextBlock Margin="5">起始:</TextBlock>
<TextBox
Name="txtFrom"
Grid.Column="1"
Margin="5">
1
</TextBox>
<TextBlock Grid.Row="1" Margin="5">结束:</TextBlock>
<TextBox
Name="txtTo"
Grid.Row="1"
Grid.Column="1"
Margin="5">
500000
</TextBox>
<StackPanel
Grid.Row="2"
Grid.Column="1"
Orientation="Horizontal">
<Button
Name="cmdFind"
Margin="5"
Padding="3"
Click="cmdFind_Click">
查找素数
</Button>
<Button
Name="cmdCancel"
Margin="5"
Padding="3"
Click="cmdCancel_Click"
IsEnabled="False">
停止
</Button>
</StackPanel>
<TextBlock Grid.Row="3" Margin="5">结果:</TextBlock>
<ListBox
Name="lstPrimes"
Grid.Row="3"
Grid.Column="1"
Margin="5" />
<TextBlock Grid.Row="4" Margin="5">进度:</TextBlock>
<ProgressBar
Name="progressBar"
Grid.Row="4"
Grid.Column="1"
Height="20"
MinHeight="20"
Margin="5"
VerticalAlignment="Bottom"
Maximum="100"
Minimum="0" />
</Grid>
.cs中的C#代码如下：
public MainWindow()
{
InitializeComponent();
backgroundWorker = new BackgroundWorker();
backgroundWorker.WorkerReportsProgress = true;
backgroundWorker.WorkerSupportsCancellation = true;
backgroundWorker.DoWork += backgroundWorker_DoWork;
backgroundWorker.RunWorkerCompleted += backgroundWorker_RunWorkerCompleted;
backgroundWorker.ProgressChanged += backgroundWorker_ProgressChanged;
}
private BackgroundWorker backgroundWorker;
private void cmdFind_Click(object sender, RoutedEventArgs e)
{
// 控制按钮、清空数据
cmdFind.IsEnabled = false;
cmdCancel.IsEnabled = true;
lstPrimes.Items.Clear();
// 获取整数方位
int from, to;
if (!Int32.TryParse(txtFrom.Text, out from))
{
MessageBox.Show("Invalid From value.");
return;
}
if (!Int32.TryParse(txtTo.Text, out to))
{
MessageBox.Show("Invalid To value.");
return;
}
// 使用RunWorkerAsync，在子线程中拾取所有素数
FindPrimesInput input = new FindPrimesInput(from, to);
backgroundWorker.RunWorkerAsync(input);
}
/// <summary>
/// BackgroundWorker执行方法
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
// 获取传入参数
FindPrimesInput input = (FindPrimesInput)e.Argument;
// 开始素数拾取
int[] primes = Worker.FindPrimes(input.From, input.To, backgroundWorker);
if (backgroundWorker.CancellationPending)
{
e.Cancel = true;
return;
}
// 返回结果
e.Result = primes;
}
/// <summary>
/// BackgroundWorker执行完成
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
MessageBox.Show("Search cancelled.");
}
else if (e.Error != null)
{
// An error was thrown by the DoWork event handler.
MessageBox.Show(e.Error.Message, "An Error Occurred");
}
else
{
int[] primes = (int[])e.Result; //结果放入ListBox
foreach (int prime in primes)
{
lstPrimes.Items.Add(prime);
}
}
//重置按钮、进度
cmdFind.IsEnabled = true;
cmdCancel.IsEnabled = false;
progressBar.Value = 0;
}
/// <summary>
/// BackgroundWorker执行进度
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar.Value = e.ProgressPercentage;//变更进度显示
}
/// <summary>
/// 取消
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void cmdCancel_Click(object sender, RoutedEventArgs e)
{
backgroundWorker.CancelAsync();
}
Worker.cs：
public class FindPrimesInput
{
public int To
{ get; set; }
public int From
{ get; set; }
public FindPrimesInput(int from, int to)
{
To = to;
From = from;
}
}
public class Worker
{
public static int[] FindPrimes(int fromNumber, int toNumber)
{
return FindPrimes(fromNumber, toNumber, null);
}
public static int[] FindPrimes(int fromNumber, int toNumber, System.ComponentModel.BackgroundWorker backgroundWorker)
{
int[] list = new int[toNumber - fromNumber];
// Create an array containing all integers between the two specified numbers.
for (int i = 0; i < list.Length; i++)
{
list[i] = fromNumber;
fromNumber += 1;
}
//find out the module for each item in list, divided by each d, where
//d is < or == to sqrt(to)
//if the remainder is 0, the nubmer is a composite, and thus
//we mark its position with 0 in the marks array,
//otherwise the number is a prime, and thus mark it with 1
int maxDiv = (int)Math.Floor(Math.Sqrt(toNumber));
int[] mark = new int[list.Length];
for (int i = 0; i < list.Length; i++)
{
for (int j = 2; j <= maxDiv; j++)
{
if ((list[i] != j) && (list[i] % j == 0))
{
mark[i] = 1;
}
}
int iteration = list.Length / 100;
if ((i % iteration == 0) && (backgroundWorker != null))
{
if (backgroundWorker.CancellationPending)
{
// Return without doing any more work.
return null;
}
if (backgroundWorker.WorkerReportsProgress)
{
//float progress = ((float)(i + 1)) / list.Length * 100;
backgroundWorker.ReportProgress(i / iteration);
//(int)Math.Round(progress));
}
}
}
//create new array that contains only the primes, and return that array
int primes = 0;
for (int i = 0; i < mark.Length; i++)
{
if (mark[i] == 0) primes += 1;
}
int[] ret = new int[primes];
int curs = 0;
for (int i = 0; i < mark.Length; i++)
{
if (mark[i] == 0)
{
ret[curs] = list[i];
curs += 1;
}
}
if (backgroundWorker != null && backgroundWorker.WorkerReportsProgress)
{
backgroundWorker.ReportProgress(100);
}
return ret;
}
}
View Code
执行效果：
BackgroundWorker的DoWork事件不可操作主线程（界面对象），用来完成一些其他耗时的后台任务，RunWorkerCompleted事件把执行结果反馈给主线程，ProgressChanged事件把执行进度反馈给主线程。
简单总结一下，Dispatcher是一种简单粗暴的处理多线程问题的方式，适合业务逻辑简单线程少的场景，BackgroundWorker则是一种安全、可控的方式，非常适用于后台文件上传下载、应用更新、实时监控等与界面交互较多场景。对于其他与界面交互不多的场景，则使用.NET的线程支持（async/await等）自主实现。
WPF知识点全攻略目录：https://www.cnblogs.com/kuangxiangnice/p/11040070.html
标签：知识点,15,int,backgroundWorker,全攻略,private,线程,BackgroundWorker,public From： https://www.cnblogs.com/kuangxiangnice/p/17371670.html