修改settings.json 里的两处 editor.rulers。 一处默认，一处dart的。

{

    "workbench.colorTheme": "Default Light+",

    "cmake.configureOnOpen": true,

    "C_Cpp.updateChannel": "Insiders",

    "http.proxySupport": "off",

    "[dart]": {

        "editor.formatOnSave": true,

        "editor.formatOnType": true,

        "editor.rulers": [

            80,128

        ],

        "editor.selectionHighlight": false,

        "editor.suggest.snippetsPreventQuickSuggestions": false,

        "editor.suggestSelection": "first",

        "editor.tabCompletion": "onlySnippets",

        "editor.wordBasedSuggestions": false

    },

    "editor.fontSize": 15,

    "terminal.integrated.defaultProfile.windows": "Command Prompt",

    "editor.wordWrapColumn": 120,

    "editor.columnSelection": true,

    "editor.rulers": [80,128],

    "dart.lineLength": 128

}