Procedimiento para imprimir en formularios Windows Forms a través de la vista previa de impresión

Artículo
05/04/2023

Es muy habitual en la programación de Windows Forms ofrecer una vista previa de impresión además de los servicios de impresión. Una forma sencilla de agregar servicios de vista previa de impresión a la aplicación es usar un control PrintPreviewDialog en combinación con la lógica de control de eventos de PrintPage para imprimir un archivo.

Para mostrar una vista previa de un documento de texto con un control PrintPreviewDialog

Agregue un PrintPreviewDialog, PrintDocument, y dos cadenas al formulario.

private PrintPreviewDialog printPreviewDialog1 = new PrintPreviewDialog();
private PrintDocument printDocument1 = new PrintDocument();

// Declare a string to hold the entire document contents.
private string documentContents;

// Declare a variable to hold the portion of the document that
// is not printed.
private string stringToPrint;

Private printPreviewDialog1 As New PrintPreviewDialog()
Private WithEvents printDocument1 As New PrintDocument()

' Declare a string to hold the entire document contents.
Private documentContents As String

' Declare a variable to hold the portion of the document that
' is not printed.
Private stringToPrint As String

Establezca la propiedad DocumentName en el documento que quiere imprimir y abra y lea el contenido del documento en la cadena que agregó previamente.

private void ReadDocument()
{
    string docName = "testPage.txt";
    string docPath = @"c:\";
    printDocument1.DocumentName = docName;
    using (FileStream stream = new FileStream(docPath + docName, FileMode.Open))
    using (StreamReader reader = new StreamReader(stream))
    {
        documentContents = reader.ReadToEnd();
    }
    stringToPrint = documentContents;
}

Private Sub ReadDocument() 
    Dim docName As String = "testPage.txt"
    Dim docPath As String = "c:\"
    printDocument1.DocumentName = docName
    Dim stream As New FileStream(docPath + docName, FileMode.Open)
    Try
        Dim reader As New StreamReader(stream)
        Try
            documentContents = reader.ReadToEnd()
        Finally
            reader.Dispose()
        End Try
    Finally
        stream.Dispose()
    End Try
    stringToPrint = documentContents

End Sub

Igual que haría para imprimir el documento, en el controlador de eventos PrintPage , use la propiedad Graphics de la clase PrintPageEventArgs y el contenido del archivo para calcular las líneas por página y representar el contenido del documento. Una vez dibujada cada página, compruebe si es la última página y establezca la propiedad HasMorePages de PrintPageEventArgs como corresponda. El evento PrintPage se produce hasta que HasMorePages es false. Cuando el documento haya terminado de representarse, restablezca la cadena que se va a representar. Además, asegúrese de que el evento PrintPage está asociado con su método de control de eventos.

Nota:

Puede que ya haya completado los pasos 2 y 3 si ha implementado la impresión en la aplicación.

En el ejemplo de código siguiente, se usa el controlador de eventos para imprimir el archivo "testPage.txt" con la misma fuente que se usa en el formulario.

void printDocument1_PrintPage(object sender, PrintPageEventArgs e)
{
    int charactersOnPage = 0;
    int linesPerPage = 0;

    // Sets the value of charactersOnPage to the number of characters
    // of stringToPrint that will fit within the bounds of the page.
    e.Graphics.MeasureString(stringToPrint, this.Font,
        e.MarginBounds.Size, StringFormat.GenericTypographic,
        out charactersOnPage, out linesPerPage);

    // Draws the string within the bounds of the page.
    e.Graphics.DrawString(stringToPrint, this.Font, Brushes.Black,
    e.MarginBounds, StringFormat.GenericTypographic);

    // Remove the portion of the string that has been printed.
    stringToPrint = stringToPrint.Substring(charactersOnPage);

    // Check to see if more pages are to be printed.
    e.HasMorePages = (stringToPrint.Length > 0);

    // If there are no more pages, reset the string to be printed.
    if (!e.HasMorePages)
        stringToPrint = documentContents;
}

Sub printDocument1_PrintPage(ByVal sender As Object, _
    ByVal e As PrintPageEventArgs) Handles printDocument1.PrintPage

    Dim charactersOnPage As Integer = 0
    Dim linesPerPage As Integer = 0

    ' Sets the value of charactersOnPage to the number of characters 
    ' of stringToPrint that will fit within the bounds of the page.
    e.Graphics.MeasureString(stringToPrint, Me.Font, e.MarginBounds.Size, _
        StringFormat.GenericTypographic, charactersOnPage, linesPerPage)

    ' Draws the string within the bounds of the page.
    e.Graphics.DrawString(stringToPrint, Me.Font, Brushes.Black, _
        e.MarginBounds, StringFormat.GenericTypographic)

    ' Remove the portion of the string that has been printed.
    stringToPrint = stringToPrint.Substring(charactersOnPage)

    ' Check to see if more pages are to be printed.
    e.HasMorePages = stringToPrint.Length > 0

    ' If there are no more pages, reset the string to be printed.
    If Not e.HasMorePages Then
        stringToPrint = documentContents
    End If

End Sub

Establezca la propiedad Document del control PrintPreviewDialog en el componente PrintDocument del formulario.
```
printPreviewDialog1.Document = printDocument1;
```
```
printPreviewDialog1.Document = printDocument1
```
Llame al método ShowDialog en el control PrintPreviewDialog . Normalmente se llamaría a ShowDialog desde el método de control de eventos Click de un botón. Al llamar a ShowDialog se genera el evento PrintPage y la salida se representa en el control PrintPreviewDialog . Cuando el usuario hace clic en el icono de impresión del cuadro de diálogo, se vuelve a generar el evento PrintPage y la salida se envía a la impresora en lugar de al cuadro de diálogo de vista previa. Este es el motivo por el que la cadena se restablece al final del proceso de representación en el paso 3.

En el siguiente ejemplo de código se muestra el método de control de eventos Click para un botón del formulario. Este método de control de eventos llama a los métodos para leer el documento y mostrar el cuadro de diálogo de vista previa de impresión.
```
private void printPreviewButton_Click(object sender, EventArgs e)
{
    ReadDocument();
    printPreviewDialog1.Document = printDocument1;
printPreviewDialog1.ShowDialog();
}
```
```
Private Sub printPreviewButton_Click(ByVal sender As Object, _
    ByVal e As EventArgs) Handles printPreviewButton.Click

    ReadDocument()
    printPreviewDialog1.Document = printDocument1
    printPreviewDialog1.ShowDialog()
End Sub
```

Ejemplo

using System;
using System.Drawing;
using System.IO;
using System.Drawing.Printing;
using System.Windows.Forms;

namespace PrintPreviewApp
{
    public partial class Form1 : Form
    {
        private Button printPreviewButton;

        private PrintPreviewDialog printPreviewDialog1 = new PrintPreviewDialog();
        private PrintDocument printDocument1 = new PrintDocument();

        // Declare a string to hold the entire document contents.
        private string documentContents;

        // Declare a variable to hold the portion of the document that
        // is not printed.
        private string stringToPrint;

        public Form1()
        {
            this.printPreviewButton = new System.Windows.Forms.Button();
            this.printPreviewButton.Location = new System.Drawing.Point(12, 12);
            this.printPreviewButton.Size = new System.Drawing.Size(125, 23);
            this.printPreviewButton.Text = "Print Preview";
            this.printPreviewButton.Click += new System.EventHandler(this.printPreviewButton_Click);
            this.ClientSize = new System.Drawing.Size(292, 266);
            this.Controls.Add(this.printPreviewButton);
            printDocument1.PrintPage +=
                new PrintPageEventHandler(printDocument1_PrintPage);
        }
        private void ReadDocument()
        {
            string docName = "testPage.txt";
            string docPath = @"c:\";
            printDocument1.DocumentName = docName;
            using (FileStream stream = new FileStream(docPath + docName, FileMode.Open))
            using (StreamReader reader = new StreamReader(stream))
            {
                documentContents = reader.ReadToEnd();
            }
            stringToPrint = documentContents;
        }

        void printDocument1_PrintPage(object sender, PrintPageEventArgs e)
        {
            int charactersOnPage = 0;
            int linesPerPage = 0;

            // Sets the value of charactersOnPage to the number of characters
            // of stringToPrint that will fit within the bounds of the page.
            e.Graphics.MeasureString(stringToPrint, this.Font,
                e.MarginBounds.Size, StringFormat.GenericTypographic,
                out charactersOnPage, out linesPerPage);

            // Draws the string within the bounds of the page.
            e.Graphics.DrawString(stringToPrint, this.Font, Brushes.Black,
            e.MarginBounds, StringFormat.GenericTypographic);

            // Remove the portion of the string that has been printed.
            stringToPrint = stringToPrint.Substring(charactersOnPage);

            // Check to see if more pages are to be printed.
            e.HasMorePages = (stringToPrint.Length > 0);

            // If there are no more pages, reset the string to be printed.
            if (!e.HasMorePages)
                stringToPrint = documentContents;
        }
        private void printPreviewButton_Click(object sender, EventArgs e)
        {
            ReadDocument();
            printPreviewDialog1.Document = printDocument1;
        printPreviewDialog1.ShowDialog();
        }

        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

Imports System.Drawing
Imports System.IO
Imports System.Drawing.Printing
Imports System.Windows.Forms



Class Form1
    Inherits Form

    Private WithEvents printPreviewButton As Button
    
    Private printPreviewDialog1 As New PrintPreviewDialog()
    Private WithEvents printDocument1 As New PrintDocument()
    
    ' Declare a string to hold the entire document contents.
    Private documentContents As String
    
    ' Declare a variable to hold the portion of the document that
    ' is not printed.
    Private stringToPrint As String

    Public Sub New() 
        Me.printPreviewButton = New System.Windows.Forms.Button()
        Me.printPreviewButton.Location = New System.Drawing.Point(12, 12)
        Me.printPreviewButton.Size = New System.Drawing.Size(125, 23)
        Me.printPreviewButton.Text = "Print Preview"
        Me.ClientSize = New System.Drawing.Size(292, 266)
        Me.Controls.Add(Me.printPreviewButton)

    End Sub
    
    Private Sub ReadDocument() 
        Dim docName As String = "testPage.txt"
        Dim docPath As String = "c:\"
        printDocument1.DocumentName = docName
        Dim stream As New FileStream(docPath + docName, FileMode.Open)
        Try
            Dim reader As New StreamReader(stream)
            Try
                documentContents = reader.ReadToEnd()
            Finally
                reader.Dispose()
            End Try
        Finally
            stream.Dispose()
        End Try
        stringToPrint = documentContents
    
    End Sub

    Sub printDocument1_PrintPage(ByVal sender As Object, _
        ByVal e As PrintPageEventArgs) Handles printDocument1.PrintPage

        Dim charactersOnPage As Integer = 0
        Dim linesPerPage As Integer = 0

        ' Sets the value of charactersOnPage to the number of characters 
        ' of stringToPrint that will fit within the bounds of the page.
        e.Graphics.MeasureString(stringToPrint, Me.Font, e.MarginBounds.Size, _
            StringFormat.GenericTypographic, charactersOnPage, linesPerPage)

        ' Draws the string within the bounds of the page.
        e.Graphics.DrawString(stringToPrint, Me.Font, Brushes.Black, _
            e.MarginBounds, StringFormat.GenericTypographic)

        ' Remove the portion of the string that has been printed.
        stringToPrint = stringToPrint.Substring(charactersOnPage)

        ' Check to see if more pages are to be printed.
        e.HasMorePages = stringToPrint.Length > 0

        ' If there are no more pages, reset the string to be printed.
        If Not e.HasMorePages Then
            stringToPrint = documentContents
        End If

    End Sub

    Private Sub printPreviewButton_Click(ByVal sender As Object, _
        ByVal e As EventArgs) Handles printPreviewButton.Click

        ReadDocument()
        printPreviewDialog1.Document = printDocument1
        printPreviewDialog1.ShowDialog()
    End Sub

    <STAThread()>  _
    Shared Sub Main() 
        Application.EnableVisualStyles()
        Application.SetCompatibleTextRenderingDefault(False)
        Application.Run(New Form1())
    
    End Sub
End Class

Compilar el código

Para este ejemplo se necesita:

Referencias a los ensamblados System, System.Windows.Forms, System.Drawing.

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Procedimiento para imprimir en formularios Windows Forms a través de la vista previa de impresión

Para mostrar una vista previa de un documento de texto con un control PrintPreviewDialog

Ejemplo

Compilar el código

Consulte también

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