/// <summary>
/// Returns the Component that should receive the focus before aComponent.
/// aContainer must be a focus cycle root of aComponent or a <a
/// href="doc-files/FocusSpec.html#FocusTraversalPolicyProviders">focus traversal policy
/// provider</a>.
/// </summary>
/// <param name="aContainer"> a focus cycle root of aComponent or focus traversal policy provider </param>
/// <param name="aComponent"> a (possibly indirect) child of aContainer, or
/// aContainer itself </param>
/// <returns> the Component that should receive the focus before aComponent,
/// or null if no suitable Component can be found </returns>
/// <exception cref="IllegalArgumentException"> if aContainer is not a focus cycle
/// root of aComponent or focus traversal policy provider, or if either aContainer or
/// aComponent is null </exception>
public override Component GetComponentBefore(Container aContainer, Component aComponent)
{
if (aContainer == null || aComponent == null)
{
throw new IllegalArgumentException("aContainer and aComponent cannot be null");
}
if (!aContainer.FocusTraversalPolicyProvider && !aContainer.FocusCycleRoot)
{
throw new IllegalArgumentException("aContainer should be focus cycle root or focus traversal policy provider");
}
else if (aContainer.FocusCycleRoot && !aComponent.IsFocusCycleRoot(aContainer))
{
throw new IllegalArgumentException("aContainer is not a focus cycle root of aComponent");
}
lock (aContainer.TreeLock)
{
if (!(aContainer.Visible && aContainer.Displayable))
{
return(null);
}
// See if the component is inside of policy provider.
Container provider = GetTopmostProvider(aContainer, aComponent);
if (provider != null)
{
if (Log.isLoggable(PlatformLogger.Level.FINE))
{
Log.fine("### Asking FTP " + provider + " for component after " + aComponent);
}
// FTP knows how to find component after the given. We don't.
FocusTraversalPolicy policy = provider.FocusTraversalPolicy;
Component beforeComp = policy.GetComponentBefore(provider, aComponent);
// Null result means that we overstepped the limit of the FTP's cycle.
// In that case we must quit the cycle, otherwise return the component found.
if (beforeComp != null)
{
if (Log.isLoggable(PlatformLogger.Level.FINE))
{
Log.fine("### FTP returned " + beforeComp);
}
return(beforeComp);
}
aComponent = provider;
// If the provider is traversable it's returned.
if (Accept(aComponent))
{
return(aComponent);
}
}
IList <Component> cycle = GetFocusTraversalCycle(aContainer);
if (Log.isLoggable(PlatformLogger.Level.FINE))
{
Log.fine("### Cycle is " + cycle + ", component is " + aComponent);
}
int index = GetComponentIndex(cycle, aComponent);
if (index < 0)
{
if (Log.isLoggable(PlatformLogger.Level.FINE))
{
Log.fine("### Didn't find component " + aComponent + " in a cycle " + aContainer);
}
return(GetLastComponent(aContainer));
}
Component comp = null;
Component tryComp = null;
for (index--; index >= 0; index--)
{
comp = cycle[index];
if (comp != aContainer && (tryComp = GetComponentDownCycle(comp, BACKWARD_TRAVERSAL)) != null)
{
return(tryComp);
}
else if (Accept(comp))
{
return(comp);
}
}
if (aContainer.FocusCycleRoot)
{
this.CachedRoot = aContainer;
this.CachedCycle = cycle;
comp = GetLastComponent(aContainer);
this.CachedRoot = null;
this.CachedCycle = null;
return(comp);
}
}
return(null);
}
