[C#] BackgroundWorker

四篇筆記

• [C#] BackgroundWorker 範例1
• [C#] BackgroundWorker 範例2
• [C#] BackgroundWorker 範例3
• [C#] BackgroundWorker 範例4
• [C#] BackgroundWorker - Exception

的 BackgroundWorker 筆記重點整理


Property

Property	說明
WorkerReportsProgress	是否報告進度更新
CancellationPending	支援非同步取消作業
WorkerSupportsCancellation	DoWork Eevent 內，用來判斷應用程式是否已要求取消
IsBusy	BackgroundWorker 是否正在執行非同步作業

Method

Method	說明
RunWorkerAsync()	執行背景作業，觸發 DoWork Event
ReportProgress()	DoWork Event 內，觸發 ProgressChanged Event
CancelAsync()	取消背景作業

Event

Event	說明
DoWork	RunWorkerAsync() 會觸發 DoWork Event，背景作業要放在這裡處理
ProgressChanged	ReportProgress() 會觸發 ProgressChanged Event，負責進度顯示
RunWorkerCompleted	背景作業完成時觸發

官方文件說明

You must be careful not to manipulate any user-interface objects in your DoWork event handler. Instead, communicate to the user interface through the ProgressChanged and RunWorkerCompleted events.

DoWork 為非同步作業，ProgressChanged 和 RunWorkerCompleted 仍然是在 main thread 內進行作業

Property 和 Method 對應表

當 Property = true 時，才可以使用 Method

Property	Method
WorkerReportsProgress	ReportProgress
WorkerSupportsCancellation	CancelAsync

Method 觸發 Event 對應表

Method	Event
RunWorkerAsync	DoWork
ReportProgress	ProgressChanged

EventAtgs

DoWorkEventArgs

EventArgs	說明
Argument	取得 RunWorkerAsync() 參數
Cancel	停止背景作業
Result	設定背景作業結果

ProgressChangedEventArgs

EventArgs	說明
ProgressPercentage	背景作業進度百分比，ReportProgress() 的 percentProgress 參數
UserState	ReportProgress() 的 userState 參數

RunWorkerCompletedEventArgs

EventArgs	說明
Cancelled	是否已取消背景作業
Error	背景作業執行時，是否發生錯誤
Result	背景作業結果，取得 DoWorkEventArgs.Result property 設定值

參數傳遞表

Exception Handle

DoWork 內發生 Exception，必須在 RunWorkerCompleted Event 內透過 RunWorkerCompletedEventArgs.Error 來處理

官方文件說明

If the operation raises an exception that your code does not handle, the BackgroundWorker catches the exception and passes it into the RunWorkerCompleted event handler, where it is exposed as the Error property of System.ComponentModel.RunWorkerCompletedEventArgs. If you are running under the Visual Studio debugger, the debugger will break at the point in the DoWork event handler where the unhandled exception was raised. If you have more than one BackgroundWorker, you should not reference any of them directly, as this would couple your DoWork event handler to a specific instance of BackgroundWorker. Instead, you should access your BackgroundWorker by casting the sender parameter in your DoWork event handler.

參考資料
• BackgroundWorker Class