/// <summary>
/// Flushes all queued messages from the JavaScript bridge
/// </summary>
/// <returns>A <see cref="Task"/>.</returns>
/// <exception cref="NotSupportedException">If the requested callback identifier is not in the list of <see cref="ScriptingDelegates"/>.</exception>
/// <seealso cref="ScriptingDelegates"/>
/// <remarks>
/// If an exception is encountered while processing the handler it is captured and returned to the caller via <see cref="JavaScriptBridgeMessage.ErrorData"/>.
/// Each message is handled independently and dispatched back to the bridge in the order in which they are received.
/// </remarks>
private async Task FlushAsync()
{
{
Trace.WriteLine($"Calling {Constants.BridgeJavaScript} method JavaScriptBridge.fetchQueue()",
Constants.TraceName);
List <JavaScriptBridgeMessage> messages;
try
{
messages = await WebView.InvokeScriptFunctionAsync <List <JavaScriptBridgeMessage> >(
"JavaScriptBridge",
"fetchQueue");
}
catch (Exception)
{
// TODO: Catch a more specific exception here
throw;
}
if (messages != null)
{
Trace.WriteLine($"Retrieved {messages.Count} message{(messages.Count != 1 ? "s" : string.Empty)}",
Constants.TraceName);
foreach (var message in messages)
{
try
{
var handlerName = message.Handler;
if (ScriptingDelegates.ContainsKey(handlerName))
{
message.ResponseData = ScriptingDelegates[handlerName](message.HandlerData);
}
else
{
throw new NotSupportedException($"Handler '{handlerName}' not supported.");
}
}
catch (Exception exception)
{
Trace.WriteLine(
$"Error while processing message: [{exception.GetType()}] {exception.Message}",
Constants.TraceName);
// Encountered an excpetion while processing the message
// Mask any potential disclosure issues by wrapping the exception as our own
var e =
new JavaScriptBridgeException(exception.Message)
{
Source = Constants.TraceName
};
message.ErrorData = e;
}
finally
{
if (!string.IsNullOrEmpty(message.CallbackId))
{
WebView.DispatchMessage(message);
}
}
}
}
}
}
/// <summary>
/// Adds the scripting delegate with a given <paramref name="handlerId"/>.
/// </summary>
/// <param name="handlerId">The identity of the delegate to be used by JavaScript.</param>
/// <param name="action">The action to be performed.</param>
/// <remarks>
/// The <paramref name="action"/> is a callback to be performed when invoking the delegate by id. The callback accepts a named parameter collection
/// via <see cref="Dictionary{String,Object}"/> and permits a return of <see cref="Object"/>. The callback itself need not accept any parameters, nor
/// need it return a value. If no parameters are passed, an empty <see cref="Dictionary{String,Object}"/> is passed for the parameters. If the callback
/// does not produce a return value, <see langword="null" /> is returned.
/// </remarks>
public void AddScriptingHandler(string handlerId, Func <Dictionary <string, object>, object> action)
{
ScriptingDelegates.Add(handlerId, action);
}
