LineDisplay Sample

2/27/2008

The LineDisplayBase class is a relatively thin abstraction layer when compared to other Service Object Base classes—there is little code needed between the application and the physical device. The LineDisplay Service Object simply needs to advertise which features the physical device supports and modify its output according to the display properties the application has set.

A LineDisplay Service Object may also monitor the device and report power or other status changes back to the application using a StatusUpdateEvent. This can be done by using the Queue methods or, for example, by using the power reporting features in PosCommon. Monitoring the device this way will generally require starting a new thread to wait for hardware events and queue the appropriate StatusUpdateEvent. A LineDisplay Service Object may also send DirectIOEvents to the application.

To implement the LineDisplay class and attributes

1. Add using directives for the Microsoft.PointOfService and Microsoft.PointOfService.BaseServiceObject namespaces.

2. Add the global attribute PosAssemblyAttribute so that PosExplorer recognizes this as a POS for .NET assembly.

3. Create a new class which is derived from LineDisplayBase.

4. Add the class-level attribute ServiceObjectAttribute to your new class so that PosExplorer recognizes it as a Service Object.

To implement abstract LineDisplayBase members

1. All LineDisplay Service Objects must support at least one screen mode. To provide the application with specifics about the supported screen modes, implement the abstract property LineDisplayScreenModes.

2. At a minimum, all LineDisplay Service Objects must implement DisplayData to display characters on the output device.

Additional Capabilities

Set capability properties in your Service Object to advertise support for the features of your device. This sample demonstrates how to implement the LineDisplay blink feature.

To implement the blink feature

1. In the constructor, set the CapBlink property to either DisplayBlink.All or DisplayBlink.Each to indicate which blinking mode this Service Object supports.

2. Set the CapBlink property to true ****** indicating that the blink rate may be set by the application by calling BlinkRate.

3. Take these and other settings into account when implementing DisplayData.

Example

using System;
using System.Collections.Generic;
using System.Text;

using Microsoft.PointOfService;
using Microsoft.PointOfService.BaseServiceObjects;

[assembly: PosAssembly("Service Object Contractors, Inc.")]

namespace SOSample.LineDisplay
{
    [ServiceObject(
          DeviceType.LineDisplay,
          "SampleLineDisplay",
          "Sample LineDiplay Service Object",
          1,
          9)]
   
    public class SampleLineDisplay : LineDisplayBase
    {
        SampleLineDisplay()
        {
            // The CapBlink property is initially set to 
            // DisplayBlink.None in LineDisplayBase. This property
            // will be set here to indicate what mode of blinking
            // text our Service Object can support.
            Properties.CapBlink = DisplayBlink.All;

            // Set the CapBlinkRate property to true to indicate 
            // that this device has the ability to change the 
            // rate at which it blinks by setting the property
            // BlinkRate.
            Properties.CapBlinkRate = true;
        }

        #region Implement Abstract LineDisplayBase Members
        // LineDisplayScreenMode must be implemented to
        // allow the application to find out which screen modes
        // are supported by this device.
        protected override LineDisplayScreenMode[] 
                                    LineDisplayScreenModes
        {
            get
            {
                LineDisplayScreenMode[] SupportedModes;

                // Create a LineDisplayScreenMode object; this SO
                // has a screen mode 10 columns wide and 2 rows deep.
                LineDisplayScreenMode mode = 
                        new LineDisplayScreenMode(10, 2, 0, 0);

                // Allocate space for our screen mode array and
                // initialize it to hold our supported screen
                // mode(s).
                SupportedModes = 
                        new LineDisplayScreenMode[] { mode };

                return SupportedModes;
            }
        }
        
        // DisplayData is the method called from the application
        // specifying what data should be displayed on the
        // device. 
        protected override void DisplayData(Cell[] cells)
        {
            // Your code here:
            // Send the data to your device. Take settings such
            // as blink and blink rate into account here.
            return;
        }
        #endregion Implement Abstract LineDisplayBase Members

        #region Implement Abstract PosCommon Members
        private string MyHealthText = "";

        // PosCommon.CheckHealthText.
        public override string CheckHealthText
        {
            get
            {
                // VerifyState(mustBeClaimed,
                // mustBeEnabled).
                VerifyState(false, false);
                return MyHealthText;
            }
        }

        //  PosCommon.CheckHealth.
        public override string CheckHealth(
                        HealthCheckLevel level)
        {
            // Verify that the device is open, claimed and enabled.
            VerifyState(true, true);

            // Your code here:
            // check the health of the device and return a
            // descriptive string.

            // Cache result in the CheckHealthText property.
            MyHealthText = "Ok";
            return MyHealthText;
        }

        // PosCommon.DirectIOData.
        public override DirectIOData DirectIO(
                                int command, 
                                int data, 
                                object obj)
        {
            // Verify that the device is open.
            VerifyState(false, false);

            return new DirectIOData(data, obj);
        }
        #endregion Abstract PosCommon Members
    }
}

See Also

Other Resources

LineDisplay Implementation
Developing Service Objects Using Base Classes