时序图

​ 序列图是一种交互图，它显示了流程以何种顺序相互操作。

Mermaid可以渲染序列图，如下定义。

sequenceDiagram
    Alice->>John:Message  Hello John, how are you?
    John-->>Alice:Message Great!
    Alice-xJohn:Message See you later!

sequenceDiagram
Alice ->> John: Hello John, how are you?
John -->> Alice: Great!
Alice-x John: See you later!

1.1 ：定义序列图的参与者

​ 参与者可以隐式定义，如上图例子----即参与者在图表源文本中按照出现的顺序呈现。但有时，您可能希望以不同于在第一条消息中显示的顺序显示参与者。可以通过以下步骤指定行动者的出现顺序:

sequenceDiagram
    participant John
    participant Alice
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!

sequenceDiagram
participant John
participant Alice
Alice->>John: Hello John, how are you?
John-->>Alice: Great!

1.2:为参与者设置别名

​ 参与者可以有一个便于识别的ID和一个描述性的标签

sequenceDiagram
    participant A as Alice
    participant J as John
    A->>J: Hello John, how are you?
    J->>A: Great!

sequenceDiagram
participant A as Alice
participant J as John
A->>J: Hello John, how are you?
J->>A: Great!

一：语法----时序图

[][][][] [参与者A] [线(箭头)] [参与者B] ：Message(关键字可忽略) 文本描述

语法可解读：即 参与者A与参与者B通过线连接 ：连接的线上可以描述A与B的关系

​ 现在有6种类型的线（箭头）

Type

Description

->

Solid line without arrow

-->

Dotted line without arrow

->>

Solid line with arrowhead

-->>

Dotted line with arrowhead

-x

Solid line with a cross at the end

--x

Dotted line with a cross at the end.

1.2：我们可以定义参与的的主动（activate）和被动（activate）的关系。

sequenceDiagram
    Alice->>John: Hello John, how are you?
    activate John
    John-->>Alice: Great!
    deactivate John

sequenceDiagram
Alice->>John: Hello John, how are you?
activate John
John-->>Alice: Great!
deactivate John

即通过“activate John”关键字activate 定义对象“John”为主动发起开始，“deactivate John”关键字deactivate定义John结束。如上。

备注：简写activate和deactivate通过在":"后追加+/-

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    John-->>-Alice: Great!

1.2.1 : activate可以连续标示同一个参与者

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!

sequenceDiagram
Alice->>+John: Hello John, how are you?
Alice->>+John: John, can you hear me?
John-->>-Alice: Hi Alice, I can hear you!
John-->>-Alice: I feel great!

二：设置笔记

我们可以为一个时序图设置笔记，语法如下

​ Note [ right of | left of | over ] [Actor]: 笔记内容

​ 语法解读：关键字 Note [ 右边 | 左边 | 上面 ] [参与者]: 笔记内容

sequenceDiagram
    participant John
    Note right of John: Text in note

sequenceDiagram
participant John
Note right of John: Text in note

备注：也可以在横跨两个对象

sequenceDiagram
    Alice->John: Hello John, how are you?
    Note over Alice,John: A typical interaction

sequenceDiagram
Alice->John: Hello John, how are you?
Note over Alice,John: A typical interaction

三：循环

​ 我们可以在时序图中表达一个循环，语法如下。

loop Loop text
... statements ...
end

举例：

sequenceDiagram
    Alice->John: Hello John, how are you?
    loop Every minute
        John-->Alice: Great!
    end

sequenceDiagram
Alice->John: Hello John, how are you?
loop Every minute
John-->Alice: Great!
end

四：Alt选择

​ 我们还可以在时序图中表达选择，即二选一的表示，语法如下

alt Describing text
... statements ...
else
... statements ...
end

OR

opt Describing text
... statements ...
end

举例如下

sequenceDiagram
    Alice->>Bob: Hello Bob, how are you?
    alt is sick
        Bob->>Alice: Not so good :(
    else is well
        Bob->>Alice: Feeling fresh like a daisy
    end
    opt Extra response
        Bob->>Alice: Thanks for asking
    end

sequenceDiagram
Alice->>Bob: Hello Bob, how are you?
alt is sick
Bob->>Alice: Not so good :(
else is well
Bob->>Alice: Feeling fresh like a daisy
end
opt Extra response
Bob->>Alice: Thanks for asking
end

五：并行

​ 在时序图中表达并行，语法如下

par [Action 1]
... statements ...
and [Action 2]
... statements ...
and [Action N]
... statements ...
end

举例1：简单并行

sequenceDiagram
        par Alice to Bob
    Alice->>Bob: Hello Bob, I am Alice.
    and Alice to John
    Alice->>John: Hello Bob, I am Alice.
    end
    Bob->>Alice: Hello Alice.
    John->>Alice: Hello Alice.

sequenceDiagram
par Alice to Bob
Alice->>Bob: Hello Bob, I am Alice.
and Alice to John
Alice->>John: Hello Bob, I am Alice.
end
Bob->>Alice: Hello Alice.
John->>Alice: Hello Alice.

举例2: 嵌套并行,即par内嵌套子par语句

六：设置背景

​ 我们可以为时序图的部分语句进行涂色，语法如下

rect rgb(0, 255, 0)
... content ...
end

例如

sequenceDiagram
par Alice to Bob
rect rgb(0, 255, 0)
Alice->>Bob: Hello Bob, I am Alice.
end
and Alice to John
Alice->>John: Hello Bob, I am Alice.
end
rect rgb(255, 0, 0)
Bob->>Alice: Hello Alice.
John->>Alice: Hello Alice.
end

七：设置备注

即为程序可读性提高，可以为时序图设置备注，语法如下


sequenceDiagram
    Alice->>John: Hello John, how are you?
    %% this is a comment
    John-->>Alice: Great!

sequenceDiagram
Alice->>John: Hello John, how are you?
%% this is a comment
John-->>Alice: Great!