Add lazy loading functionality

__tests__/__snapshots__/masonry.test.js.snap

@@ -23,6 +23,8 @@ exports[`SNAPSHOT: All functionality should match prev snapshot 1`] = `
       }
     }
     enableEmptySections={true}
+    onEndReached={[Function]}
+    onEndReachedThreshold={25}
     refreshControl={undefined}
     removeClippedSubviews={false}
     renderRow={[Function]}

components/Masonry.js

@@ -36,7 +36,9 @@ export default class Masonry extends Component {
 		customImageProps: PropTypes.object,
 		spacing: PropTypes.number,
 		priority: PropTypes.string,
-		refreshControl: PropTypes.element
+		refreshControl: PropTypes.element,
+		onEndReached: PropTypes.func,
+		onEndReachedThreshold: PropTypes.number
 	};
 
 	static defaultProps = {
@@ -45,7 +47,10 @@ export default class Masonry extends Component {
 		sorted: false,
 		imageContainerStyle: {},
 		spacing: 1,
-		priority: 'order'
+		priority: 'order',
+		// no-op function
+		onEndReached: () => ({}),
+		onEndReachedThreshold: 25
 	};
 
 	constructor(props) {
@@ -60,7 +65,8 @@ export default class Masonry extends Component {
 			initialOrientation: true,
 			_sortedData: [],
 			_resolvedData: [],
-			_columnHeights: columnHeights
+			_columnHeights: columnHeights,
+			_uniqueCount: props.bricks.length
 		};
 		// Assuming that rotation is binary (vertical|landscape)
 		Dimensions.addEventListener('change', (window) => this.setState(state => ({ initialOrientation: !state.initialOrientation })));
@@ -76,24 +82,28 @@ export default class Masonry extends Component {
 		// We use the difference in the passed in bricks to determine if user is appending or not
 		const brickDiff = differenceBy(nextProps.bricks, this.props.bricks, 'uri');
 		const appendedData = brickDiff.length !== nextProps.bricks.length;
+		const _uniqueCount = brickDiff.length + this.props.bricks.length;
 
 		// These intents would entail a complete re-render of the listview
 		if (differentColumns || differentPriority || !appendedData) {
 			this.setState(state => ({
 				_sortedData: [],
 				_resolvedData: [],
-				_columnHeights: generateColumnHeights(nextProps.columns)
+				_columnHeights: generateColumnHeights(nextProps.columns),
+				_uniqueCount
 			}), this.resolveBricks(nextProps));
 		}
 
 		// We use the existing data and only resolve what is needed
 		if (appendedData) {
-			this.resolveBricks({...nextProps, bricks: brickDiff});
-			return;
+			const offSet = this.props.bricks.length;
+			this.setState({
+				_uniqueCount
+			}, this.resolveBricks({...nextProps, bricks: brickDiff}, offSet));
 		}
 	}
 
-	resolveBricks({ bricks, columns }) {
+	resolveBricks({ bricks, columns }, offSet = 0) {
 		if (bricks.length === 0) {
 			// clear and re-render
 			this.setState(state => ({
@@ -105,7 +115,7 @@ export default class Masonry extends Component {
 		// Issues arrise if state changes occur in the midst of a resolve
 		bricks
 			.map((brick, index) => assignObjectColumn(columns, index, brick))
-			.map((brick, index) => assignObjectIndex(index, brick))
+			.map((brick, index) => assignObjectIndex(offSet + index, brick))
 			.map(brick => resolveImage(brick))
 			.map(resolveTask => resolveTask.fork(
 				(err) => console.warn('Image failed to load'),
@@ -174,29 +184,40 @@ export default class Masonry extends Component {
 		return dataCopy;
 	};
 
+  _delayCallEndReach = () => {
+		const sortedData = this.state._sortedData;
+		const sortedLength = sortedData.reduce((acc, cv) => cv.length + acc, 0);
+		// Limit the invokes to only when the masonry has
+		// fully loaded all of the content to ensure user fully reaches the end
+		if (sortedLength === this.state._uniqueCount) {
+			this.props.onEndReached();
+		}
+	}
 
 	render() {
 		return (
-			<View style={{flex: 1}} onLayout={(event) => this._setParentDimensions(event)}>
-	<ListView
-	  contentContainerStyle={styles.masonry__container}
-	  dataSource={this.state.dataSource}
-	  enableEmptySections
-	  scrollRenderAheadDistance={100}
-	  removeClippedSubviews={false}
-	  renderRow={(data, sectionId, rowID) => (
-		  <Column
-			data={data}
-			columns={this.props.columns}
-			parentDimensions={this.state.dimensions}
-			imageContainerStyle={this.props.imageContainerStyle}
-			customImageComponent={this.props.customImageComponent}
-			customImageProps={this.props.customImageProps}
-			spacing={this.props.spacing}
-			key={`RN-MASONRY-COLUMN-${rowID}`} />
-	  )}
+		<View style={{flex: 1}} onLayout={(event) => this._setParentDimensions(event)}>
+		<ListView
+			contentContainerStyle={styles.masonry__container}
+			dataSource={this.state.dataSource}
+			enableEmptySections
+			scrollRenderAheadDistance={100}
+			removeClippedSubviews={false}
+			onEndReached={this._delayCallEndReach}
+			onEndReachedThreshold={this.props.onEndReachedThreshold}
+			renderRow={(data, sectionId, rowID) => (
+			<Column
+				data={data}
+				columns={this.props.columns}
+				parentDimensions={this.state.dimensions}
+				imageContainerStyle={this.props.imageContainerStyle}
+				customImageComponent={this.props.customImageComponent}
+				customImageProps={this.props.customImageProps}
+				spacing={this.props.spacing}
+				key={`RN-MASONRY-COLUMN-${rowID}`} />
+			)}
 			refreshControl={this.props.refreshControl} />
-				</View>
+		</View>
 		);
 	}
 };

example/App/Container/app.js

@@ -107,17 +107,27 @@ let data = [
 	}
 ];
 
-const addData = [
-	{
-		uri: 'https://i.pinimg.com/736x/48/ee/51/48ee519a1768245ce273363f5bf05f30--kaylaitsines-dipping-sauces.jpg'
-	},
-	{
-		uri: 'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQGYfU5N8lsJepQyoAigiijX8bcdpahei_XqRWBzZLbxcsuqtiH'
-	},
-	{
-		uri: 'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSPL2GTXDuOzwuX5X7Mgwc3Vc9ZIhiMmZUhp3s1wg0oHPzSP7qC'
-	}
-];
+const createBrick = uri => ({ uri });
+
+const data1 = [
+	'https://i.pinimg.com/736x/48/ee/51/48ee519a1768245ce273363f5bf05f30--kaylaitsines-dipping-sauces.jpg',
+	'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQGYfU5N8lsJepQyoAigiijX8bcdpahei_XqRWBzZLbxcsuqtiH',
+	'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSPL2GTXDuOzwuX5X7Mgwc3Vc9ZIhiMmZUhp3s1wg0oHPzSP7qC',
+].map(createBrick);
+
+const data2 = [
+	'https://i.pinimg.com/236x/ee/ea/61/eeea61b03a2de8216384ff1be9544b82--what-you-see-follow-me.jpg',
+	'https://i.pinimg.com/originals/a0/30/87/a03087e36c083a665cd3392d2d59cf0b.jpg',
+	'https://i.pinimg.com/736x/59/ae/8e/59ae8ee0e9e84aa234f80a345fa7f1c6--wedding-ceremony-wedding-menu.jpg'
+].map(createBrick);
+
+const data3 = [
+	'https://i.pinimg.com/736x/6a/53/0a/6a530a49f764ce51a9742162f46c1e05--soul-food-pinterest.jpg',
+	'https://i.pinimg.com/originals/a0/30/87/a03087e36c083a665cd3392d2d59cf0b.jpg',
+	'https://img.buzzfeed.com/buzzfeed-static/static/2018-02/19/3/asset/buzzfeed-prod-fastlane-03/sub-buzz-12799-1519030318-7.jpg'
+].map(createBrick);
+
+const appendData = [data1, data2, data3];
 
 export default class example extends Component {
 	constructor() {
@@ -126,15 +136,23 @@ export default class example extends Component {
 		this.state = {
 			columns: 2,
 			padding: 5,
-			data
+			data,
+			dataIndex: 0
 		};
 	}
 
 	_addData = () => {
-		const appendedData = [...data, ...addData];
-		this.setState({
-			data: appendedData
-		});
+		if (this.state.dataIndex < 3) {
+			this.setState(state => {
+				const addData = appendData[this.state.dataIndex];
+				const appendedData = [...state.data, ...addData];
+
+				return {
+					data: appendedData,
+					dataIndex: state.dataIndex + 1
+				};
+			});
+		}
 	}
 
 	render() {
@@ -181,10 +199,10 @@ export default class example extends Component {
 
 			  <View style={{flex: 1, flexGrow: 10, padding: this.state.padding}}>
 				<Masonry
-				  sorted
 				  bricks={this.state.data}
 				  columns={this.state.columns}
-				  priority='order'
+				  onEndReached={this._addData}
+				  priority='balance'
 				  customImageComponent={FastImage} />
 			  </View>
 			</View>