[android] Get notified when all image previews have been loaded

Also fix crash when attaching image fails

briar-android/src/main/java/org/briarproject/briar/android/view/ImagePreview.java

@@ -79,6 +79,13 @@ public class ImagePreview extends ConstraintLayout {
 
 	interface ImagePreviewListener {
 
+		void onPreviewLoaded();
+
+		/**
+		 * Called when Glide can't load a preview image.
+		 *
+		 * Warning: Glide may call this multiple times.
+		 */
 		void onUriError(Uri uri);
 
 		void onCancel();

briar-android/src/main/java/org/briarproject/briar/android/view/ImagePreviewAdapter.java

@@ -54,6 +54,7 @@ class ImagePreviewAdapter extends Adapter<ImagePreviewViewHolder> {
 
 	void removeUri(Uri uri) {
 		int pos = items.indexOf(uri);
+		if (pos == -1) return;
 		items.remove(uri);
 		notifyItemRemoved(pos);
 	}

briar-android/src/main/java/org/briarproject/briar/android/view/ImagePreviewViewHolder.java

@@ -54,8 +54,8 @@ class ImagePreviewViewHolder extends ViewHolder {
 					public boolean onLoadFailed(@Nullable GlideException e,
 							Object model, Target<Drawable> target,
 							boolean isFirstResource) {
-						listener.onUriError(uri);
 						progressBar.setVisibility(INVISIBLE);
+						listener.onUriError(uri);
 						return false;
 					}
 
@@ -64,6 +64,7 @@ class ImagePreviewViewHolder extends ViewHolder {
 							Object model, Target<Drawable> target,
 							DataSource dataSource, boolean isFirstResource) {
 						progressBar.setVisibility(INVISIBLE);
+						listener.onPreviewLoaded();
 						return false;
 					}
 				})

briar-android/src/main/java/org/briarproject/briar/android/view/TextAttachmentController.java

@@ -54,6 +54,7 @@ public class TextAttachmentController extends TextSendController
 	private CharSequence textHint;
 	private boolean hasImageSupport = false;
 	private List<Uri> imageUris = emptyList();
+	private int previewsLoaded = 0;
 
 	public TextAttachmentController(TextInputView v, ImagePreview imagePreview,
 			SendListener listener, AttachImageListener imageListener) {
@@ -185,6 +186,8 @@ public class TextAttachmentController extends TextSendController
 		imageUris = emptyList();
 		// show the image button again, so images can get attached
 		showImageButton(true);
+		// no preview has been loaded
+		previewsLoaded = 0;
 	}
 
 	@Override
@@ -204,21 +207,40 @@ public class TextAttachmentController extends TextSendController
 		return state.getSuperState();
 	}
 
+	@Override
+	public void onPreviewLoaded() {
+		previewsLoaded++;
+		checkAllPreviewsLoaded();
+	}
+
 	@Override
 	public void onUriError(Uri uri) {
-		imageUris.remove(uri);
+		boolean removed = imageUris.remove(uri);
+		if (!removed) {
+			// we have removed this Uri already, do not remove it again
+			return;
+		}
 		imagePreview.removeUri(uri);
 		if (imageUris.isEmpty()) onCancel();
 		Toast.makeText(textInput.getContext(), R.string.image_attach_error,
 				LENGTH_LONG).show();
+		checkAllPreviewsLoaded();
 	}
 
 	@Override
 	public void onCancel() {
 		textInput.clearText();
+		sendButton.setEnabled(true);
 		reset();
 	}
 
+	private void checkAllPreviewsLoaded() {
+		if (previewsLoaded == imageUris.size()) {
+			// all previews were loaded
+			// TODO allow sending
+		}
+	}
+
 	public void showImageOnboarding(Activity activity,
 			Runnable onOnboardingSeen) {
 		PromptStateChangeListener listener = (prompt, state) -> {