iOS相当于增加堆大小

Question

iOS apps (for the most part) is written in Objective-C, which is a subset of C, and is therefore a data managed language, unlike Android/Java.

In Android, you have the ability to increase heap size by simply adding this one line in the XML android manifest:

<application android:largeHeap="true"/>

Is there an iOS version to doing something like this?

Answer 1

Well in iOS you don't have any control over the memory.

It is all managed by the kernel. So you cannot increase the heap size.

As pointed out in the comments, memory management has a different notion in iOS.

You get as many memory as available but if the app uses to much memory it will be killed by the system.

Now that you explained your goal, you shouldn't download large files into memory, this will cause trouble. Instead you should save it directly to the disk as you get the response.

Answer 2

Take a look at Apple's " Memory Usage Performance Guidelines " for an explanation of how iOS doesn't manage swap space.

Although OS X supports a backing store, iOS does not. In iPhone applications, read-only data that is already on the disk (such as code pages) is simply removed from memory and reloaded from disk as needed. Writable data is never removed from memory by the operating system. Instead, if the amount of free memory drops below a certain threshold, the system asks the running applications to free up memory voluntarily to make room for new data. Applications that fail to free up enough memory are terminated.

iOS attempts to provide each application with as much of the device's memory as the OS can spare. However each application is limited to the device's physical memory. There is no option to allocated larger blocks and expect them to be swapped to disk as needed.

Manipulating the heap size in iOS is therefore not a meaningful concept. Each app already has the largest heap the OS can provide. Instead apps must attempt to minimize their memory footprint to remain within the available space on the host device. This means purging in-memory caches in response to memory warnings, streaming access to resources on disk (as @CouchDeveloper suggested in a comment), and minimizing the amount of memory used overall.

As an additional complication iOS attempts to keep memory in use. Unused memory is wasted capacity and users may be better served by the OS keeping more applications suspended and in memory rather than terminated. As a result attempting to measure available free memory does not give a meaningful result. As the device runs low on free memory other applications will reduce their use in response to memory warnings or by being terminated completely.