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POScrollViewSuite Example Code Uses More Memory than Necessary?
 

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    <p>There is problem in <a href="http://developer.apple.com/library/ios/#samplecode/ScrollViewSuite/Introduction/Intro.html" rel="nofollow">ScrollViewSuite</a>. it use more memory than needed . for example:</p> <ol> <li>Load image in 25% and measure memory (4 MB) </li> <li>Zoom in image to 100% and measure memory (30 MB)</li> <li>Zoom out to 25% and measure memory (30 MB) - why 30 ? it must use only 4 MB - that is the problem.</li> </ol> <p>How to fix the problem ?</p> <pre><code>/***********************************************************************************/ /* Most of the work of tiling is done in layoutSubviews, which we override here. */ /* We recycle the tiles that are no longer in the visible bounds of the scrollView */ /* and we add any tiles that should now be present but are missing. */ /***********************************************************************************/ - (void)layoutSubviews { [self updateResolution]; NSLog(@"layoutSubviews "); [super layoutSubviews]; CGRect visibleBounds = [self bounds]; // first recycle all tiles that are no longer visible for (UIView *tile in [tileContainerView subviews]) { // We want to see if the tiles intersect our (i.e. the scrollView's) bounds, so we need to convert their // frames to our own coordinate system CGRect scaledTileFrame = [tileContainerView convertRect:[tile frame] toView:self]; // If the tile doesn't intersect, it's not visible, so we can recycle it if (! CGRectIntersectsRect(scaledTileFrame, visibleBounds)) { [reusableTiles addObject:tile]; [tile removeFromSuperview]; } } // calculate which rows and columns are visible by doing a bunch of math. float scaledTileWidth = [self tileSize].width * [self zoomScale]; float scaledTileHeight = [self tileSize].height * [self zoomScale]; int maxRow = floorf([tileContainerView frame].size.height / scaledTileHeight); // this is the maximum possible row int maxCol = floorf([tileContainerView frame].size.width / scaledTileWidth); // and the maximum possible column int firstNeededRow = MAX(0, floorf(visibleBounds.origin.y / scaledTileHeight)); int firstNeededCol = MAX(0, floorf(visibleBounds.origin.x / scaledTileWidth)); int lastNeededRow = MIN(maxRow, floorf(CGRectGetMaxY(visibleBounds) / scaledTileHeight)); int lastNeededCol = MIN(maxCol, floorf(CGRectGetMaxX(visibleBounds) / scaledTileWidth)); // iterate through needed rows and columns, adding any tiles that are missing for (int row = firstNeededRow; row &lt;= lastNeededRow; row++) { for (int col = firstNeededCol; col &lt;= lastNeededCol; col++) { BOOL tileIsMissing = (firstVisibleRow &gt; row || firstVisibleColumn &gt; col || lastVisibleRow &lt; row || lastVisibleColumn &lt; col); if (tileIsMissing) { UIView *tile = [dataSource tiledScrollView:self tileForRow:row column:col resolution:resolution]; // set the tile's frame so we insert it at the correct position CGRect frame = CGRectMake([self tileSize].width * col, [self tileSize].height * row, [self tileSize].width, [self tileSize].height); [tile setFrame:frame]; [tileContainerView addSubview:tile]; // annotateTile draws green lines and tile numbers on the tiles for illustration purposes. [self annotateTile:tile]; } } } // update our record of which rows/cols are visible firstVisibleRow = firstNeededRow; firstVisibleColumn = firstNeededCol; lastVisibleRow = lastNeededRow; lastVisibleColumn = lastNeededCol; } </code></pre>
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