IVBPrint interface

The interface the Print statement dispatches through. A class that implements IVBPrint becomes a valid Print target, so myObject.Print "a", "b" compiles and runs against it.

This is how Form, PictureBox, Printer, PropertyPage, Report and UserControl accept Print: the first five implement it on the shared drawing base, and Printer implements it and forwards to that base.

Note

IVBPrint is an internal interface and may change in future BETA releases. It is declared Private inside the VB package, so reaching it from a project means exposing the package’s private symbols through its library symbol, which is not the default — see Implementing it below.

Members

WriteText
Syntax: WriteText( Value As String )

Writes a chunk of already-formatted text at the current print position. The statement calls this once per expression, and once more with the line terminator unless a trailing separator suppressed it.

Column
Syntax: object.Column [ = value ]

The current print column, as a Long. The statement reads it to find where it has got to, and assigns it to move to a new column — which is what a comma, Tab(n) or Spc(n) does.

A column is whatever the implementer decides it is worth. The VB drawing classes convert between a column and CurrentX using the font’s average character width, rounding up when reporting, which is why print zones stay aligned in a proportional font.

The dispatch protocol

Print evaluates the expressions and does the column arithmetic itself, then drives the target. For myObject.Print "a", "b" the calls are, in order:

WriteText("a")        ' the first expression
Column                ' read  -- returns 0
Column = 14           ' write -- the comma moves to the next print zone
WriteText("b")        ' the second expression
WriteText(vbCrLf)     ' the line ends, since there is no trailing separator

Two things follow from this that are worth knowing.

The statement never pads the text with spaces. Capturing everything handed to WriteText above yields ab, with nothing between the fields; the gap a reader sees is produced by the target when it honours the new Column. On the Debug Console that means emitting spaces, and on a drawing surface it means moving the pen.

The column arithmetic is done in columns, not in pixels or characters. The statement asks for column 14 and leaves it to the target to decide where column 14 falls.

Implementing it

A class implements the three members and gains Print:

Class PrintSink

    Implements VB.IVBPrint

    Private m_buf As String
    Private m_col As Long

    Private Sub SinkWriteText(ByVal Value As String) _
            Implements VB.IVBPrint.WriteText
        m_buf = m_buf & Value
    End Sub

    Private Property Get SinkColumn() As Long _
            Implements VB.IVBPrint.Column
        Return m_col
    End Property

    Private Property Let SinkColumn(ByVal Value As Long) _
            Implements VB.IVBPrint.Column
        m_col = Value
    End Property

    Public Function Text() As String
        Return m_buf
    End Function

End Class

Used like any other Print target:

Dim Sink As New PrintSink
Sink.Print "a", "b"
Debug.Print Sink.Text()

Two things have to be right, and the compiler reports the same error for both.

Expose the package’s private symbols. In Project Settings → Library References, on the Enabled Libraries tab, click the pencil beside the VB package’s library symbol and prefix it with an asterisk — *VB. The asterisk is the instruction, not part of the name; see Library symbols. Without it the interface is invisible.

Qualify the name. Implements IVBPrint on its own does not resolve even after that; write VB.IVBPrint, or whatever the library symbol has been renamed to. With the symbol set to *MyVB, the declaration is Implements MyVB.IVBPrint.

Get either wrong and every mention fails with TB5079 Unrecognized datatype symbol ‘IVBPrint’.

See Also