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53 lines
1.8 KiB
Objective-C
53 lines
1.8 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 ASDisplayShouldFetchBatchForContext(ASBatchContext *context,
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ASScrollDirection scrollDirection,
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CGRect bounds,
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CGSize contentSize,
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CGPoint targetOffset,
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CGFloat leadingScreens) {
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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 Up and Left scrolls are currently supported (tail loading)
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if (scrollDirection != ASScrollDirectionUp && scrollDirection != ASScrollDirectionLeft) {
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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 ||
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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 (scrollDirection == ASScrollDirectionUp) {
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viewLength = bounds.size.height;
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offset = targetOffset.y;
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contentLength = contentSize.height;
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} else { // horizontal
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viewLength = bounds.size.width;
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offset = targetOffset.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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