Memory leak

What is memory leak

The reason for memory leakage is essentially that objects with a long life cycle refer to objects with a short life cycle , Resulting in a short life cycle The object cannot be GC Recycle in time , As a result, the occupied memory cannot be released , If the program runs for a long time, it may eventually lead to OOM out of memory .

Under what circumstances are memory leaks prone to occur ？

There are many reasons for memory leaks. Here are a few common situations .

One 、Handler Cause memory leaks .

We know ,Handler、Message、MessageQueue It's interconnected ,Handler By sending a message Message Interact with the main thread , If Handler Message sent Message Not yet dealt with , The Message And send it Handler The object will be MessageQueue Has been held , This could lead to Handler Cannot be recycled , This leads to memory leaks .

for instance ：

AActivity There's a delay in the code 1 Second execution message Message, When the interface starts from AActivity Jump to BActivity when ,AActivity Automatic backstage , At this point, if the system resources are tight （ Or open the “ Don't keep the activity ” Options ）,AActivity Will be finish. But here's the problem , hypothesis AActivity Of Handler object mHandler Is a non static anonymous inner class object , It automatically holds the outer class AActivity References to , Which leads to SecondActivity Cannot be recycled , Memory leak .

terms of settlement ：

take Handler Declared as a static inner class , You don't hold external classes SecondActivity References to , Its lifecycle has nothing to do with external classes , If Handler It needs to context Words , External classes can be referenced by weak references , Or directly at Activity Of onDestroy Lieutenant general Handler Destruction of objects .

Two 、Bitmap There is no call recycle()

Bitmap When the object is confirmed not to be used , We should call recycle() Free memory , Then set to null, Otherwise, memory leaks can result .

terms of settlement ：

stay Acrivity or Fragment In the call recycle().

3、 ... and 、 Memory leak caused by objects in the collection not being cleaned up

We often add references to some objects to the collection , But when we don't need to change the object , It doesn't clean up its references from the collection , In this way, the collection will become larger and larger . If this set is static, This will cause the resources in the collection to occupy memory all the time and cannot be cleaned up .

terms of settlement ：

Set the collection resource empty when it is useless .

Four 、 Memory leak caused by resource object not being closed

Resource objects such as （Cursor,File Documents, etc. ） Often with some buffer , When we don't use it , They should be shut down in time , So that their buffers reclaim memory in time . Instead of waiting GC To deal with it .

5、 ... and 、 There is no memory leak caused by registration cancellation

such Android Memory leak ratio Java The memory leak is even more serious , Because some of the others Android The program may refer to the Android The object of the program （ E.g. registration mechanism ）. Even if Android The program is over , But other applications still have access to Android A reference to an object of a program , It can also cause memory leaks .

resolvent ：

1. Use ApplicationContext Instead of ActivityContext;
2. stay Activity perform onDestory when , Call de registration ;

Ways to detect memory leaks

LeakCanary Tools

The official address is as follows ：https://github.com/square/leakcanary/LeakCanary Need to integrate... In project code . When a memory leak occurs ,LeakCanary A window will pop up to prompt and generate the corresponding heap storage information record .

Android Profiler analyzer

open Android Studio, Compile code , Run on a simulator or a real machine App, Then click on the icon below , Enter the following interface

This method can intuitively observe the memory fluctuation during the running of the program, and can clearly list all the objects causing memory consumption and memory allocation , It takes some experience to use ,