Node placeholder API

ASDisplayNodes now have an overidable method -placeholderImage that lets you provide a custom UIImage to display while a node is displaying asyncronously. The default implementation of this method returns nil and thus does nothing. A provided example project also demonstrates using the placeholder API.

examples/Placeholders/Sample/ViewController.m

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+/* This file provided by Facebook is for non-commercial testing and evaluation
+ * purposes only.  Facebook reserves all rights not expressly granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#import "ViewController.h"
+
+#import <AsyncDisplayKit/AsyncDisplayKit.h>
+
+#import "PostNode.h"
+#import "SlowpokeImageNode.h"
+#import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
+
+@interface ViewController ()
+{
+  PostNode *_postNode;
+  SlowpokeImageNode *_imageNode;
+  UIButton *_displayButton;
+}
+
+@end
+
+
+@implementation ViewController
+
+#pragma mark -
+#pragma mark UIViewController
+
+- (instancetype)init
+{
+  if (!(self = [super init]))
+    return nil;
+
+  _displayButton = [UIButton buttonWithType:UIButtonTypeCustom];
+  [_displayButton setTitle:@"Display me!" forState:UIControlStateNormal];
+  [_displayButton addTarget:self action:@selector(onDisplayButton:) forControlEvents:UIControlEventTouchUpInside];
+
+  UIColor *tintBlue = [UIColor colorWithRed:0 green:122/255.0 blue:1.0 alpha:1.0];
+  [_displayButton setTitleColor:tintBlue forState:UIControlStateNormal];
+  [_displayButton setTitleColor:[tintBlue colorWithAlphaComponent:0.5] forState:UIControlStateHighlighted];
+  _displayButton.backgroundColor = [UIColor colorWithWhite:0.95 alpha:1.0];
+
+  return self;
+}
+
+- (void)viewDidLoad
+{
+  [super viewDidLoad];
+
+  [self.view addSubview:_displayButton];
+}
+
+- (void)viewWillLayoutSubviews
+{
+  CGFloat padding = 20.0;
+  CGRect bounds = self.view.bounds;
+  CGFloat constrainedWidth = CGRectGetWidth(bounds);
+  CGSize constrainedSize = CGSizeMake(constrainedWidth - 2 * padding, CGFLOAT_MAX);
+
+  CGSize postSize = [_postNode measure:constrainedSize];
+  CGSize imageSize = [_imageNode measure:constrainedSize];
+
+  _imageNode.frame = (CGRect){padding, padding, imageSize};
+  _postNode.frame = (CGRect){padding, CGRectGetMaxY(_imageNode.frame) + 10.0, postSize};
+
+  CGFloat buttonHeight = 55.0;
+  _displayButton.frame = (CGRect){0.0, CGRectGetHeight(bounds) - buttonHeight, CGRectGetWidth(bounds), buttonHeight};
+}
+
+// this method is pretty gross and just for demonstration  :]
+- (void)createAndDisplayNodes
+{
+  [_imageNode.view removeFromSuperview];
+  [_postNode.view removeFromSuperview];
+
+  // ASImageNode gets placeholders by default
+  _imageNode = [[SlowpokeImageNode alloc] init];
+  _imageNode.image = [UIImage imageNamed:@"logo"];
+
+  _postNode = [[PostNode alloc] init];
+
+  // change to NO to see text placeholders, change to YES to see the parent placeholder
+  // this placeholder will cover all subnodes while they are displaying, just a like a stage curtain!
+  _postNode.placeholderEnabled = NO;
+
+  [self.view addSubview:_imageNode.view];
+  [self.view addSubview:_postNode.view];
+}
+
+
+#pragma mark -
+#pragma mark Actions
+
+- (void)onDisplayButton:(id)sender
+{
+  [self createAndDisplayNodes];
+}
+
+@end