Application.DoEvents 方法

參考

定義

命名空間:: System.Windows.Forms

組件:: System.Windows.Forms.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

處理目前在訊息佇列中的所有 Windows 訊息。

public:
 static void DoEvents();

public static void DoEvents ();

static member DoEvents : unit -> unit

Public Shared Sub DoEvents ()

範例

下列程式碼範例示範如何使用 DoEvents 方法。執行範例時，使用者可以從 OpenFileDialog 中選取圖形檔案。選取的檔案會顯示在表單中。方法 DoEvents 會強制開啟每個圖形檔案的表單重繪。若要執行此範例，請將下列程式碼貼到表單中， PictureBox 其中包含名為的、 OpenFileDialog 名為 PictureBox1OpenFileDialog1 的，以及名為的 fileButton 按鈕。 InitializePictureBox從表單的建構函式或 Load 方法呼叫和 InitializeOpenFileDialog 方法。

注意

在 Visual Studio 中，如果您使用拖曳作業將新增 OpenFileDialog 至表單，則必須移除建立新實例的 OpenFileDialog 行來修改下列 InitializeOpenFileDialog 方法。

此範例也需要 Control.Click 控制項的 Button 事件和 FileOk 的 OpenFileDialog 事件連接到範例中定義的事件處理常式。執行範例時，按一下按鈕來顯示對話方塊。

void InitializePictureBox()
{
   this->PictureBox1 = gcnew System::Windows::Forms::PictureBox;
   this->PictureBox1->BorderStyle =
      System::Windows::Forms::BorderStyle::FixedSingle;
   this->PictureBox1->SizeMode = PictureBoxSizeMode::StretchImage;
   this->PictureBox1->Location = System::Drawing::Point( 72, 112 );
   this->PictureBox1->Name = "PictureBox1";
   this->PictureBox1->Size = System::Drawing::Size( 160, 136 );
   this->PictureBox1->TabIndex = 6;
   this->PictureBox1->TabStop = false;
}

void InitializeOpenFileDialog()
{
   this->OpenFileDialog1 = gcnew System::Windows::Forms::OpenFileDialog;
   
   // Set the file dialog to filter for graphics files.
   this->OpenFileDialog1->Filter =
      "Images (*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|" +
      "All files (*.*)|*.*";
   
   // Allow the user to select multiple images.
   this->OpenFileDialog1->Multiselect = true;
   this->OpenFileDialog1->Title = "My Image Browser";
}

void fileButton_Click( System::Object^ sender, System::EventArgs^ e )
{
   OpenFileDialog1->ShowDialog();
}

// This method handles the FileOK event.  It opens each file 
// selected and loads the image from a stream into PictureBox1.
void OpenFileDialog1_FileOk( Object^ sender,
   System::ComponentModel::CancelEventArgs^ e )
{
   this->Activate();
   array<String^>^ files = OpenFileDialog1->FileNames;
   
   // Open each file and display the image in PictureBox1.
   // Call Application.DoEvents to force a repaint after each
   // file is read.        
   for each ( String^ file in files )
   {
      System::IO::FileInfo^ fileInfo = gcnew System::IO::FileInfo( file );
      System::IO::FileStream^ fileStream = fileInfo->OpenRead();
      PictureBox1->Image = System::Drawing::Image::FromStream( fileStream );
      Application::DoEvents();
      fileStream->Close();
      
      // Call Sleep so the picture is briefly displayed, 
      //which will create a slide-show effect.
      System::Threading::Thread::Sleep( 2000 );
   }
   PictureBox1->Image = nullptr;
}

private void InitializePictureBox()
{
    this.pictureBox1 = new System.Windows.Forms.PictureBox();
    this.pictureBox1.BorderStyle = 
        System.Windows.Forms.BorderStyle.FixedSingle;
    this.pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
    this.pictureBox1.Location = new System.Drawing.Point(72, 112);
    this.pictureBox1.Name = "pictureBox1";
    this.pictureBox1.Size = new System.Drawing.Size(160, 136);
    this.pictureBox1.TabIndex = 6;
    this.pictureBox1.TabStop = false;
}

private void InitializeOpenFileDialog()
{
    this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();

    // Set the file dialog to filter for graphics files.
    this.openFileDialog1.Filter = 
        "Images (*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|" + 
        "All files (*.*)|*.*";

    // Allow the user to select multiple images.
    this.openFileDialog1.Multiselect = true;
    this.openFileDialog1.Title = "My Image Browser";
}

private void fileButton_Click(System.Object sender, System.EventArgs e)
{
    openFileDialog1.ShowDialog();
}


// This method handles the FileOK event.  It opens each file 
// selected and loads the image from a stream into pictureBox1.
private void openFileDialog1_FileOk(object sender, 
    System.ComponentModel.CancelEventArgs e)
{

    this.Activate();
     string[] files = openFileDialog1.FileNames;

    // Open each file and display the image in pictureBox1.
    // Call Application.DoEvents to force a repaint after each
    // file is read.        
    foreach (string file in files )
    {
        System.IO.FileInfo fileInfo = new System.IO.FileInfo(file);
        System.IO.FileStream fileStream = fileInfo.OpenRead();
        pictureBox1.Image = System.Drawing.Image.FromStream(fileStream);
        Application.DoEvents();
        fileStream.Close();

        // Call Sleep so the picture is briefly displayed, 
        //which will create a slide-show effect.
        System.Threading.Thread.Sleep(2000);
    }
    pictureBox1.Image = null;
}

Private Sub InitializePictureBox()
    Me.PictureBox1 = New System.Windows.Forms.PictureBox
    Me.PictureBox1.BorderStyle = _
        System.Windows.Forms.BorderStyle.FixedSingle
    Me.PictureBox1.SizeMode = PictureBoxSizeMode.StretchImage
    Me.PictureBox1.Location = New System.Drawing.Point(72, 112)
    Me.PictureBox1.Name = "PictureBox1"
    Me.PictureBox1.Size = New System.Drawing.Size(160, 136)
    Me.PictureBox1.TabStop = False
End Sub

Private Sub InitializeOpenFileDialog()
    Me.OpenFileDialog1 = New System.Windows.Forms.OpenFileDialog

    ' Set the file dialog to filter for graphics files.
    Me.OpenFileDialog1.Filter = _
    "Images (*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files (*.*)|*.*"

    ' Allow the user to select multiple images.
    Me.OpenFileDialog1.Multiselect = True
    Me.OpenFileDialog1.Title = "My Image Browser"
End Sub

Private Sub fileButton_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles FileButton.Click
    OpenFileDialog1.ShowDialog()
End Sub


' This method handles the FileOK event.  It opens each file 
' selected and loads the image from a stream into PictureBox1.
Private Sub OpenFileDialog1_FileOk(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) _
 Handles OpenFileDialog1.FileOk

    Me.Activate()
    Dim file, files() As String
    files = OpenFileDialog1.FileNames

    ' Open each file and display the image in PictureBox1.
    ' Call Application.DoEvents to force a repaint after each
    ' file is read.        
    For Each file In files
        Dim fileInfo As System.IO.FileInfo = New System.IO.FileInfo(file)
        Dim fileStream As System.IO.FileStream = fileInfo.OpenRead()
        PictureBox1.Image = System.Drawing.Image.FromStream(fileStream)
        Application.DoEvents()
        fileStream.Close()

        ' Call Sleep so the picture is briefly displayed, 
        'which will create a slide-show effect.
        System.Threading.Thread.Sleep(2000)
    Next
    PictureBox1.Image = Nothing
End Sub

備註

當您執行 Windows Form 時，它會建立新的表單，然後等候事件進行處理。每次表單處理事件時，都會處理與該事件相關聯的所有程式碼。所有其他事件都會在佇列中等候。雖然您的程式碼會處理事件，但您的應用程式不會回應。例如，如果另一個視窗拖曳在頂端，則視窗不會重新繪製。

如果您在程式碼中呼叫 DoEvents ，您的應用程式可以處理其他事件。例如，如果您有一個將資料新增至的表單，並新增 DoEvents 至 ListBox 您的程式碼，則當另一個視窗拖曳到表單上方時，您的表單會重新繪製。如果您從程式碼中移除 DoEvents ，在按鈕的 click 事件處理常式執行完成之前，您的表單將不會重新繪製。如需傳訊的詳細資訊，請參閱Windows Forms 中的使用者輸入。

不同于 Visual Basic 6.0， DoEvents 方法不會呼叫 Thread.Sleep 方法。

一般而言，您會在迴圈中使用此方法來處理訊息。

警告

呼叫這個方法會導致處理所有等候視窗訊息時暫停目前的執行緒。如果訊息導致觸發事件，則應用程式程式碼的其他區域可能會執行。這可能會導致您的應用程式呈現難以偵錯的非預期行為。如果您執行需要很長時間的作業或計算，最好是在新的執行緒上執行這些作業。如需非同步程式設計的詳細資訊，請參閱非同步程式設計模型 (APM) 。

適用於

Application.DoEvents 方法

定義

範例

備註

適用於

另請參閱

意見反應

其他資源