Andorid development art exploration notes (2), cross platform applet development framework

2. singleTop： Stack top reuse mode

In this mode, if Activity Already at the top of the stack, this Activity Will not recreate , At the same time, its onNewIntent Method will be called , Through the parameters of this method, we can get the current request information . If the new Activity Not at the top of the stack , Then it will be recreated . If the current stack is ABCD, The model is standard, To create a D, The stack becomes ABCDD, If singleTop Then for ABCD.

3. singleTask： In stack reuse mode

This is a single instance mode .Activity When starting, first find out whether there is an instance in the stack , If so, set it to the top of the stack , Do not create a new instance , If it does not exist, create a new instance and push it onto the stack .

①S1 In the stack Activity by ABC, Want to start D, Then create an instance stack ,S1 Turn into ABCD.

②S1 In the stack ABC, but D The desired stack is S2,S2 non-existent , therefore S2 and D At the same time, create and transfer D Push the S2 In the stack .

③S1 In the stack ABCD, Want to be in S1 Start in B, Will CD Out of the stack ,S1 The stack becomes AB.

（ All the above are in singTask In mode ）

4. singleInstance： Single instance mode .

It's a kind of reinforcement singleTask Pattern , So it has singleTask The function of mode , A little bit stronger , That's the pattern Activity It can only be located on one task stack .Activity A In this mode, it can only be located on the stack S1 in ,Activity B Can only be located separately on the stack S2 in .

< About TaskAffinity>

It marks a Activity The name of the required task stack . By default, it's all Activity The package name of the app . So it's connected to singleTask Pairs using . One more parameter allowTaskReparenting, If it is True also singleTask Next , that When one Activity A start-up B One of them Activity, When B Startup time , This Activity Your task stack will start from A Transfer to B.

You can do this by Menifest Start mode is specified in , You can also get it from Acitivity Of addFlags Set the flag bit to specify the startup mode . In terms of priority , The latter is higher than the former . And the limited scope of the two methods is also different , The former cannot be specified FLAG_ACTIVITY_CLEAR_TOP identification , The latter cannot be Activity Appoint singleInstance Pattern .

In the book is singleTask An example is introduced to illustrate its operation ：

A by standard Pattern , So its TaskAffinity Is the default package name S1,B and C Are all singleTask Pattern ,TaskAffinity by S2.A Start... First B,B Then start C, At this time, the stack is ：S1 There are only A, because B and C need S2 Task stack , therefore B Created S2 Stack ,S2 In the stack BC. then C start-up A, This time because A yes standard Pattern , So it will go to the one that created it Actvitiy namely C In the stack of , therefore S2 Stack becomes BCA,S1 Stack as A. next A start-up B, because B by singleTask Pattern , therefore S2 Medium CA All pop up the stack to let B To the top of the stack , here S2 Stack as B. Then press the back key ,S2 Stack Actviity Be taken out , Backstage S1 The stack is put into the foreground . and S1 Only A, But this A Not at all S2 Stack but S1 Stack . next A Press the return key in the , Of all stacks Activity Be taken out , Back to the desktop .

Here are some examples singleTask To understand the task stack diagram ：

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< About Activity Of Flags>

• FLAG_ACTIVITY_NEW_TASK

Designated as singleTask Pattern