不预览即打印WebBrowser，即单击打印
我有一个ac＃.Net应用程序，它将打开一个自定义打印预览表单（破坏了显示HTML文件的WebBrowser表单控件和一个打印Web浏览器控件内容的按钮：
webBrowser.Print();但是，我现在想在不打开此表单的情况下打印HTML文件。
我试图将html加载到webbrowser表单中而不显示该表单，并调用了webBrowser.Print（），但不会打印任何内容。似乎只有显示表单并将HTML加载到控件中才能打印。
回答：
我有一个示例控制台应用程序，该应用程序使用WinForms打印一组HTML文件WebBrowser。您DoWorkAsync实际上可以在WinForms应用程序中借用它的一部分来完成打印任务，而无需进行任何更改：
// by Noseratio - http://stackoverflow.com/users/1768303/noseratiousing System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace ConsoleApplicationWebBrowser
{
class Program
{
// Entry Point of the console app
static void Main(string[] args)
{
try
{
// download each page and dump the content
var task = MessageLoopWorker.Run(DoWorkAsync,
"http://www.example.com", "http://www.example.net", "http://www.example.org");
task.Wait();
Console.WriteLine("DoWorkAsync completed.");
}
catch (Exception ex)
{
Console.WriteLine("DoWorkAsync failed: " + ex.Message);
}
Console.WriteLine("Press Enter to exit.");
Console.ReadLine();
}
// navigate WebBrowser to the list of urls in a loop
static async Task<object> DoWorkAsync(object[] args)
{
Console.WriteLine("Start working.");
var wb = new WebBrowser();
wb.ScriptErrorsSuppressed = true;
if (wb.Document == null && wb.ActiveXInstance == null)
throw new ApplicationException("Unable to initialize the underlying WebBrowserActiveX");
// get the underlying WebBrowser ActiveX object;
// this code depends on SHDocVw.dll COM interop assembly,
// generate SHDocVw.dll: "tlbimp.exe ieframe.dll",
// and add as a reference to the project
var wbax = (SHDocVw.WebBrowser)wb.ActiveXInstance;
TaskCompletionSource<bool> loadedTcs = null;
WebBrowserDocumentCompletedEventHandler documentCompletedHandler = (s, e) =>
loadedTcs.TrySetResult(true); // turn event into awaitable task
TaskCompletionSource<bool> printedTcs = null;
SHDocVw.DWebBrowserEvents2_PrintTemplateTeardownEventHandler printTemplateTeardownHandler = (p) =>
printedTcs.TrySetResult(true); // turn event into awaitable task
// navigate to each URL in the list
foreach (var url in args)
{
loadedTcs = new TaskCompletionSource<bool>();
wb.DocumentCompleted += documentCompletedHandler;
try
{
wb.Navigate(url.ToString());
// await for DocumentCompleted
await loadedTcs.Task;
}
finally
{
wb.DocumentCompleted -= documentCompletedHandler;
}
// the DOM is ready,
Console.WriteLine(url.ToString());
Console.WriteLine(wb.Document.Body.OuterHtml);
// print the document
printedTcs = new TaskCompletionSource<bool>();
wbax.PrintTemplateTeardown += printTemplateTeardownHandler;
try
{
wb.Print();
// await for PrintTemplateTeardown - the end of printing
await printedTcs.Task;
}
finally
{
wbax.PrintTemplateTeardown -= printTemplateTeardownHandler;
}
Console.WriteLine(url.ToString() + " printed.");
}
wb.Dispose();
Console.WriteLine("End working.");
return null;
}
}
// a helper class to start the message loop and execute an asynchronous task
public static class MessageLoopWorker
{
public static async Task<object> Run(Func<object[], Task<object>> worker, params object[] args)
{
var tcs = new TaskCompletionSource<object>();
var thread = new Thread(() =>
{
EventHandler idleHandler = null;
idleHandler = async (s, e) =>
{
// handle Application.Idle just once
Application.Idle -= idleHandler;
// return to the message loop
await Task.Yield();
// and continue asynchronously
// propogate the result or exception
try
{
var result = await worker(args);
tcs.SetResult(result);
}
catch (Exception ex)
{
tcs.SetException(ex);
}
// signal to exit the message loop
// Application.Run will exit at this point
Application.ExitThread();
};
// handle Application.Idle just once
// to make sure we're inside the message loop
// and SynchronizationContext has been correctly installed
Application.Idle += idleHandler;
Application.Run();
});
// set STA model for the new thread
thread.SetApartmentState(ApartmentState.STA);
// start the thread and await for the task
thread.Start();
try
{
return await tcs.Task;
}
finally
{
thread.Join();
}
}
}
}
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