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60 lines
2.0 KiB
Objective-C
60 lines
2.0 KiB
Objective-C
/* Copyright (c) 2014-present, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*/
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#import "ASBatchFetching.h"
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BOOL ASDisplayShouldFetchBatchForScrollView(UIScrollView<ASBatchFetchingScrollView> *scrollView, ASScrollDirection scrollDirection, CGPoint contentOffset)
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{
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// Don't fetch if the scroll view does not allow
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if (![scrollView canBatchFetch]) {
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return NO;
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}
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// Check if we should batch fetch
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ASBatchContext *context = scrollView.batchContext;
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CGRect bounds = scrollView.bounds;
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CGSize contentSize = scrollView.contentSize;
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CGFloat leadingScreens = scrollView.leadingScreensForBatching;
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// Do not allow fetching if a batch is already in-flight and hasn't been completed or cancelled
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if ([context isFetching]) {
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return NO;
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}
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// Only Down and Right scrolls are currently supported (tail loading)
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if (!ASScrollDirectionContainsDown(scrollDirection) && !ASScrollDirectionContainsRight(scrollDirection)) {
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return NO;
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}
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// No fetching for null states
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if (leadingScreens <= 0.0 || CGRectEqualToRect(bounds, CGRectZero)) {
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return NO;
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}
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CGFloat viewLength, offset, contentLength;
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if (ASScrollDirectionContainsDown(scrollDirection)) {
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viewLength = bounds.size.height;
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offset = contentOffset.y;
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contentLength = contentSize.height;
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} else { // horizontal / right
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viewLength = bounds.size.width;
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offset = contentOffset.x;
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contentLength = contentSize.width;
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}
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// target offset will always be 0 if the content size is smaller than the viewport
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BOOL hasSmallContent = offset == 0.0 && contentLength < viewLength;
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CGFloat triggerDistance = viewLength * leadingScreens;
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CGFloat remainingDistance = contentLength - viewLength - offset;
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return hasSmallContent || remainingDistance <= triggerDistance;
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}
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