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[wechat applet] operation mechanism and update mechanism
2022-07-06 20:34:00 【Front end Xiao Liu is not afraid of cattle】
Hello, old man , Niuniu is more civilized again , We have explained some commonly used components above , As a developer , We also need to understand the running mechanism and update mechanism of the applet , That's the question , How much do you know about them ?
Today, Niuniu will take you to have a test , Don't take notes of what you don't understand !
List of articles
One , Operating mechanism
The first one is about the running mechanism of the applet , The applet is started and finally destroyed , There are actually many different steps , Applets experience many states , The general operation mechanism is shown in the figure below .
Next, let's begin to explain the detailed steps
1.1 Start of applet
Look at the picture above , We know , The applet will first have a Cold start
, A simple explanation is The user opens the applet for the first time , Or the applet is automatically destroyed after a certain period of time and then opened again by the user , This is the time , The applet needs to reload the code , Reload boot .
At this time, a little friend may ask , What if you start the applet again before destroying it ? This time is called Hot start
La , When using small programs at ordinary times , We will find that , Close the applet and reopen it soon , The loading speed is much faster than the former , This is because the applet was not destroyed , It is from the background state to the foreground state , This process is called hot start , It can also be said to cut the front desk .
1.2 Applet front and background
After the applet finishes loading , There will be two states , Namely Front desk status and Backstage status .
- After the applet starts , When the interface is displayed , The applet is in
Front desk status
- And when we close the applet , In a certain amount of time , The applet is not really closed, that is, destroyed , But to enter what is said
Backstage status
, The applet is still running in the background , Part of itAPI
The use of will be limited . The operation here is to cut the background in the previous figure . - Under normal circumstances , The time of background state will not last for a long time , After a short period of time, the pending event will be turned on , Go into suspend state ( Explain later ).
- Before destruction , The user clicks the applet again to open it , The applet will start from
Backstage status
orPending state
Re enterFront desk status
, This is the hot start we talked about earlier
1.3 Pending state
The applet is Backstage status
After a short time , It will switch to Pending state
, In this state , Wechat will stop the applet JS Thread execution , The content state of the applet will be temporarily preserved , event 、 Callback, etc. re-enter the applet In foreground status
Will trigger .
Small tip:
- The backstage doesn't stop JS Thread execution , If the applet is turned on Backstage music 、 Location And other functions , The applet will not cut in from the background and hang , That is, the applet can run continuously
1.4 Applet destruction event
The last one is when the suspended state lasts too long ( It's thirty minutes now ), In order to reduce resource tension , Now , The applet will be destroyed .
There's another situation , When the applet takes up too much system resources , It will also be destroyed by the system or actively recycled by wechat clients .
In development , We can use wx.onMemoryWarning
Monitor memory alarm events , Set memory cleanup .
Two , Renewal mechanism
We know , Wechat client will cache the code of the applet in the local cache , And developers will release updated new versions of small programs from time to time in the management background , So how does wechat client know whether there is a new version ?
In fact, wechat clients will have several opportunities to check the local cache , If there's a new version , Then update the applet code package , But if you happen to open the applet without these opportunities after releasing the new version , It may be an old version of the applet .
The following is a list of the time to check for updates
2.1 Synchronize updates at startup
Synchronous updates will affect the startup time of the applet , Synchronous updates do not necessarily occur at startup , In the following two cases , The update will be synchronized when the applet is started .
Check regularly and find new versions
When wechat is running , It will regularly check whether the recently used applet has a new version , And set whether to update synchronously the next time you start the appletThe user hasn't used it for a long time
I haven't used the applet for a long time , Wechat client iterates normally for applet version , These applets will be updated synchronously at startup .
2.2 Asynchronous update at startup
Every time the applet is cold started , There will be asynchronous check whether there is a new version of operation , If you find a new version , The new version code will be downloaded asynchronously , Without affecting the operation of the applet , But it can also lead to , If it is still the old version after startup , Only the next start , Will open the new version of the applet .
2.3 Developers manually trigger
Wechat provides a APIwx.getUpdateManager
, You can prompt the user to restart the applet to update the new version when there is a new version
3、 ... and , Life cycle
Finally, let's end today with the life cycle .
The life cycle can be divided into two parts: program and page , For programs , When we first started the applet , Will trigger
onLaunch
Method , When our applet is initialized , Will triggeronShow
Method , The page loads and displays , At this time, the... Of the display page is triggeredonLoad
andonShow
Method , Successfully displayed page .Show page for the first time , It will also trigger the page
onReady
Method , Render page elements , Be careful , The method , A page can only be called once .When the applet cuts into the background , Be careful , The applet will trigger the page first
onHide
Method , Hide page , Trigger the program againonHide
MethodWhen the applet cuts into the foreground from the background , The applet will trigger the program first
onShow
Method , Then trigger the... Of the pageonShow
Method , Display the page .
Here is an online picture for everyone to understand
That's the end of this article , If it helps you , You can pay attention to the follow-up updates of Niuniu , Thank you for your support !
Debt see ~
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