ios - React Native 在 iOS 应用程序进入后台时将新的图像副本加载到内存中

Question

我创建了一个新的 React Native 项目 (v0.60.4)，并在真正的 iPhone 11 Pro iOS 13.1.3 上以 Release模式运行它。 app.js 非常简单:

import React from 'react';
import {
  SafeAreaView,
  Image,
} from 'react-native';

const App: () => React$Node = () => {
  return (
      <SafeAreaView>
        <Image source={require('./test.png')} />
      </SafeAreaView>
  );
};

export default App;

我注意到，每次我的应用程序进入后台(当我切换到另一个应用程序时)，我都会看到内存使用量激增，而且从未释放过(即使有内存警告)。

我可以看到增加是由应用程序移入后台时创建的新 ImageIO_PNG_Data 引起的。

虽然此图像的大小相对适中，但在我的实际应用程序中，它会在用户应用程序频繁切换后导致应用程序崩溃。

这是用 Swift 编写的同一个应用程序、同一个图像，使用相同的方法创建 RN 正在使用的 UIImage。

没有额外的图像加载到内存中。 RN 做了什么不同的事情，将这些额外的图像加载到内存中，而不是清除旧的图像？当应用程序进入后台时会发生什么？

更新

标记一代后，我注意到所有大图像都来自看起来像 iOS 应用程序进入后台时的快照:

   0 libsystem_kernel.dylib mmap
   1 ImageIO _ImageIO_Malloc
   2 ImageIO AppleJPEGReadPlugin::copyImageBlockSet(InfoRec*, CGImageProvider*, CGRect, CGSize, __CFDictionary const*)
   3 ImageIO IIO_Reader::CopyImageBlockSetProc(void*, CGImageProvider*, CGRect, CGSize, __CFDictionary const*)
   4 ImageIO IIOImageProviderInfo::CopyImageBlockSetWithOptions(void*, CGImageProvider*, CGRect, CGSize, __CFDictionary const*)
   5 CoreGraphics CGImageProviderCopyImageBlockSetWithOptions
   6 QuartzCore CA::Render::copy_image(CGImage*, CGColorSpace*, unsigned int, double, double)
   7 QuartzCore CA::Render::prepare_image(CGImage*, CGColorSpace*, unsigned int, double)
   8 QuartzCore CA::Layer::prepare_commit(CA::Transaction*)
   9 QuartzCore CA::Context::commit_transaction(CA::Transaction*, double)
  10 QuartzCore CA::Transaction::commit()
  11 UIKitCore __83-[UIApplication _createSnapshotContextForScene:withName:performLayoutWithSettings:]_block_invoke_4
  12 UIKitCore -[UIApplication _performWithUICACommitStateSnapshotting:]
  13 UIKitCore __83-[UIApplication _createSnapshotContextForScene:withName:performLayoutWithSettings:]_block_invoke_2
  14 UIKitCore +[UIView(Animation) performWithoutAnimation:]
  15 UIKitCore __83-[UIApplication _createSnapshotContextForScene:withName:performLayoutWithSettings:]_block_invoke
  16 UIKitCore -[UIScene _applyOverrideSettings:forActions:]
  17 UIKitCore -[UIWindowScene _applySnapshotSettings:forActions:]
  18 UIKitCore -[UIApplication _createSnapshotContextForScene:withName:performLayoutWithSettings:]
  19 UIKitCore __65-[UIApplication _performSnapshotsWithAction:forScene:completion:]_block_invoke_3
  20 FrontBoardServices -[FBSSceneSnapshotAction _executeNextRequest]
  21 FrontBoardServices -[FBSSceneSnapshotAction _executeNextRequest]
  22 FrontBoardServices -[FBSSceneSnapshotAction executeRequestsWithHandler:completionHandler:expirationHandler:]
  23 UIKitCore __65-[UIApplication _performSnapshotsWithAction:forScene:completion:]_block_invoke_2
  24 UIKitCore -[UIApplication _beginSnapshotSessionForScene:withSnapshotBlock:]
  25 UIKitCore __65-[UIApplication _performSnapshotsWithAction:forScene:completion:]_block_invoke
  26 UIKitCore -[UIScene _enableOverrideSettingsForActions:]
  27 UIKitCore -[UIScene _performSystemSnapshotWithActions:]
  28 UIKitCore -[UIApplication _performSnapshotsWithAction:forScene:completion:]
  29 UIKitCore __98-[_UISceneSnapshotBSActionsHandler _respondToActions:forFBSScene:inUIScene:fromTransitionContext:]_block_invoke_3
  30 UIKitCore __98-[_UISceneSnapshotBSActionsHandler _respondToActions:forFBSScene:inUIScene:fromTransitionContext:]_block_invoke.30
  31 UIKitCore -[UIApplication prepareSnapshotsWithAction:forScene:completion:]
  32 UIKitCore __98-[_UISceneSnapshotBSActionsHandler _respondToActions:forFBSScene:inUIScene:fromTransitionContext:]_block_invoke_2
  33 UIKitCore -[UIScene _emitSceneSettingsUpdateResponseForCompletion:afterSceneUpdateWork:]
  34 UIKitCore -[UIScene scene:didUpdateWithDiff:transitionContext:completion:]
  35 UIKitCore -[UIApplicationSceneClientAgent scene:handleEvent:withCompletion:]
  36 FrontBoardServices -[FBSSceneImpl updater:didUpdateSettings:withDiff:transitionContext:completion:]
  37 FrontBoardServices __88-[FBSWorkspaceScenesClient sceneID:updateWithSettingsDiff:transitionContext:completion:]_block_invoke_2
  38 FrontBoardServices -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:]
  39 FrontBoardServices __88-[FBSWorkspaceScenesClient sceneID:updateWithSettingsDiff:transitionContext:completion:]_block_invoke
  40 libdispatch.dylib 0x102a9b2a7
  41 libdispatch.dylib 0x102a9e9cf
  42 FrontBoardServices __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__
  43 FrontBoardServices -[FBSSerialQueue _queue_performNextIfPossible]
  44 FrontBoardServices -[FBSSerialQueue _performNextFromRunLoopSource]
  45 CoreFoundation __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
  46 CoreFoundation __CFRunLoopDoSource0
  47 CoreFoundation __CFRunLoopDoSources0
  48 CoreFoundation __CFRunLoopRun
  49 CoreFoundation CFRunLoopRunSpecific
  50 GraphicsServices GSEventRunModal
  51 UIKitCore UIApplicationMain
  52 tmp main /...
  53 libdyld.dylib start

Answer 1

当然，当应用程序进入后台时，操作系统实际上会拍摄应用程序的照片，在滚动后台应用程序时用作预览。在我们的应用程序中，我们做了这样的事情:

- (void)deleteAllTemporaryFiles
{
  RCTLogInfo(@"[Delegate] Deleting all temp files...");
  [self deleteDirectoryFiles:NSTemporaryDirectory()];
  [self deleteDirectoryFiles:NSSearchPathForDirectoriesInDomains(NSCachesDirectory,   NSUserDomainMask, YES)[0]];
  [self deleteDirectoryFiles:NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0]];
}

- (void)deleteDirectoryFiles:(NSString *)directory
{
  NSArray<NSString *> *temp = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:directory error:NULL];
  for (NSString *path in temp) {
    if (/* check for directories you want to keep here */) continue;
    @try {
      NSString *filePath = [directory stringByAppendingPathComponent:path];
      RCTLogInfo(@"[Delegate] Deleting %@",filePath);
      [[NSFileManager defaultManager] removeItemAtPath:filePath error:NULL];
    }
    @catch (NSException *e) {
      RCTLogInfo(@"[Delegate] Deletion error: %@", e);
    }
  }
}

在委托(delegate)中:

// Delete all temp files when app is paused
- (void)applicationDidEnterBackground:(UIApplication *)application
{
  [self deleteAllTemporaryFiles];
}