/// <summary>
/// Prepares the instance before it runs.
/// </summary>
public override async Task<bool> PrepareAndTryLoadingFromCacheAsync()
{
ImageView imageView;
_imageWeakReference.TryGetTarget(out imageView);
if (imageView == null)
return false;
var cacheResult = await TryLoadingFromCacheAsync(imageView).ConfigureAwait(false);
if (cacheResult == CacheResult.Found || cacheResult == CacheResult.ErrorOccured) // If image is loaded from cache there is nothing to do here anymore, if something weird happened with the cache... error callback has already been called, let's just leave
return true; // stop processing if loaded from cache OR if loading from cached raised an exception
bool hasDrawable = await LoadPlaceHolderAsync(Parameters.LoadingPlaceholderPath, Parameters.LoadingPlaceholderSource, imageView, true).ConfigureAwait(false);
if (!hasDrawable)
{
// Assign the Drawable to the image
var drawable = new AsyncDrawable(Context.Resources, null, this);
await MainThreadDispatcher.PostAsync(() =>
{
if (imageView == null || imageView.Handle == IntPtr.Zero)
return;
imageView.SetImageDrawable(drawable);
}).ConfigureAwait(false);
}
return false;
}
/// <summary>
/// Loads given placeHolder into the imageView.
/// </summary>
/// <returns>An awaitable task.</returns>
/// <param name="placeholderPath">Full path to the placeholder.</param>
/// <param name="source">Source for the path: local, web, assets</param>
protected async Task<bool> LoadPlaceHolderAsync(string placeholderPath, ImageSource source, ImageView imageView, bool isLoadingPlaceholder)
{
if (string.IsNullOrWhiteSpace(placeholderPath))
return false;
if (imageView == null)
return false;
BitmapDrawable drawable = ImageCache.Instance.Get(GetKey(placeholderPath));
if (drawable != null)
{
// We should wrap drawable in an AsyncDrawable, nothing is deferred
drawable = new AsyncDrawable(Context.Resources, drawable.Bitmap, this);
}
else
{
// Here we asynchronously load our placeholder: it is deferred so we need a temporary AsyncDrawable
drawable = new AsyncDrawable(Context.Resources, null, this);
await MainThreadDispatcher.PostAsync(() =>
{
if (imageView == null || imageView.Handle == IntPtr.Zero)
return;
imageView.SetImageDrawable(drawable); // temporary assign this AsyncDrawable
}).ConfigureAwait(false);
try
{
var drawableWithResult = await RetrieveDrawableAsync(placeholderPath, source, isLoadingPlaceholder).ConfigureAwait(false);
drawable = drawableWithResult == null ? null : drawableWithResult.Item;
}
catch (Exception ex)
{
Logger.Error("An error occured while retrieving drawable.", ex);
return false;
}
}
if (drawable == null)
return false;
_loadingPlaceholderWeakReference = new WeakReference<Drawable>(drawable);
if (CancellationToken.IsCancellationRequested)
return false;
await MainThreadDispatcher.PostAsync(() =>
{
if (CancellationToken.IsCancellationRequested)
return;
if (imageView == null || imageView.Handle == IntPtr.Zero)
return;
SetImageDrawable(imageView, drawable, false);
}).ConfigureAwait(false);
return true;
}
