Windows Mobile 5 Notifications

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Introduction

In this article, I describe how to use the Windows Mobile 5 State and Notification API (SNAPI) to get notified of changes in network states. Integrating network notification is the basis to implementing background data replication. Furthermore, when an application has knowledge of available networks, it can then choose the best connection to move data between the device and a back-end server.

Background

The State and Notifications APIs provide a powerful built-in notification broker structure for the Windows Mobile 5.0 environment. Some of the requirements of SNAPI are:

• .NET Compact Framework Version 2.0
• Exposed via Microsoft.WindowsMobile.Status namespace
• Specific to the Windows Mobile 5.0 platform
• Included in the OS installation (not in the deployment CABs for the .NET CF 2.0) and Emulator

Using the Code

To implement application notifications, a reference to the following namespaces must be added:

• Microsoft.WindowsMobile
• Microsoft.WindowsMobile.Status

The following code outlines how to enable the notification callbacks within the application:

public void SetUpNotifications()
{
    // This tells which states to monitor
    SystemState s;
    // Monitor for ActiveSync Connection
    s = new SystemState(SystemProperty.CradlePresent);
    s.Changed += new ChangeEventHandler(ChangeOccurred);
    stateList.Add(s);
    // Monitor for GPRS Connection
    s = new SystemState(SystemProperty.PhoneGprsCoverage);
    s.Changed += new ChangeEventHandler(ChangeOccurred);
    stateList.Add(s);
    //Monitor for Network Connection (e.g. WiFi)
    s = new SystemState(SystemProperty.ConnectionsNetworkCount);
    s.Changed += new ChangeEventHandler(ChangeOccurred);
    stateList.Add(s);

    UpdateConnectionState();
}

public void ChangeOccurred(object sender, ChangeEventArgs args)
{
    // If a change occurs
    SystemState state = (SystemState)sender;
    UpdateConnectionState();
}

public void UpdateConnectionState()
{
    // Set the check boxes based on the current state of the networks
    activesync.Checked = Convert.ToBoolean
        (SystemState.GetValue(SystemProperty.CradlePresent));
    gprs.Checked = Convert.ToBoolean(SystemState.GetValue
        (SystemProperty.PhoneGprsCoverage));
    wifi.Checked = Convert.ToBoolean(SystemState.GetValue
        (SystemProperty.ConnectionsNetworkCount));
}

Timers are a useful way of using the notification APIs to help determine when to initiate replication. On a specific interval, a function can be called to initiate data movement based on network availability. The following code shows how the current state of the network can help determine which data to retrieve.

private void Sync()
{
    // Initiate A Connection Using the preferred (available) network connection

    if (activesync.Checked)
    {
        // Retrieve all data
    }
    else if (wifi.Checked)
    {
        // Retrieve medium priority data
    }
    else if (gprs.Checked)
    {
        // Retrieve high priority data
    }
    else
    {
        txtStatus.Text = "No Connectivity.";
        return;
    }
}

Conclusion

SNAPI is a excellent addition to a mobile application and can help to optimize data exchange. By adding a mobile database, an application can then be built to move data in the background to the point that users do not even realize synchronization is being executed.