学会编写mvvm简易框架

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原文链接: segmentfault.com

书接上一篇: 150行代码教你实现一个低配版的MVVM库(1)- 原理篇

写在前面

为了便于分模块,和阅读,我使用了Typescript来进行coding,总行数是正好150行,最早写DEMO的时候用了ES2015,代码行数应该在100行出头,如果你不会搭ts+webpack的编译UMD环境,你也可以把本文中的ts语法人肉转成es6或者es2015,我相信这对你(一个有志于学写mvvm库的青年)来说没有什么难度。

作为作者呢,虽然最后我会放出源码的地址,你可以去github上扫一眼代码,但我还是希望你们可以跟我一起,打开个文本编辑器,一个模块一个模块把代码人肉敲出来,这样的感觉是不一样的,就好比是你可能之前就阅读过angular,vue的源码,但你现在还不是在读我的文章么?

第一步 先把骨架搭好, 血肉晚点再填充

还是再上一遍设计图

设计的类不多,一共就5个

//SegmentFault.ts
export let SegmentFault = class SegmentFault {
    private viewModelPool = {};   //用来维护viewModel的别名alias与viewModel之间的关系
    private viewViewModelMap = {};//用来维护viewModel和被绑定的view之间的关系
    public registerViewModel(alias:string, vm:object) {};//在sf正式运作之前我们先要注册一个下viewModel并给他起一个别名
    public init() {};  //sf库开始运作的入口函数
    
    public refresh(alias:string){}; // 暴露一个强制刷新整个viewModel的方法,因为毕竟有你监控不到的角落
}

SegmentFault是对用户暴露的唯一的对象,就像Angular他会暴露一个angular对象给用户使用一样。
最终,用户会这样来操作SF以达到双向绑定的目的
不妨再看看使用效果

<script src="dist/sf.js"></script> <!-- 这里引入我们的sf.js库-->
<script>
    var sf = new SegmentFault();   //生成一个sf的实例
    sf.registerViewModel("vm", new ViewModel());  //注册一个viewModel,起一个叫vm的别名
    sf.init();  //调用init方法,开始初始化,sf正式开始一些列工作

    //以下是viewModel的定义
    function ViewModel() {
        this.message = "hello, SegmentFault";
        this.buttonClickHandler = function() {
            this.message = "clicked: " + this.message;
        }
    }
</script>

有没有觉得SF的API干净利落,清新爽洁!

根据设计图的Step 1,先给已注册的viewModel加上监视,这里我们需要一个Watcher类

export class Watcher {
    private sf;
    
    //构造函数里传入一个sf的对象,便于callback调用时的作用域确定。。。这是后话
    constructor(sf) {
        this.sf = sf;
    }
    public observe(viewModel, callback) {} //暗中观察
}

再来看一下Step 2, 另一个主要的类Scanner,Scanner是干什么的呢?作用就一个遍历整个DOM Tree把出现sf-xxxx这个attribute的Elements全部挑出来,然后找sf-xxxx = expression,等号右边这个表达式里如果出现了viewModel的alias,那就说么这个element是跟viewModel搭界了,是绑定在一起了,scanner负责把这对"恋人"关系用一个数据结构维护一下,等全部扫描完了一起返回给SegmentFault去听候发落。

//Scanner.ts
export class Scanner {

    private prefix = "sf-"; //库的前缀
    private viewModelPool;
    
    constructor(viewModelPool) {
        this.viewModelPool = viewModelPool; //Scanner肯定是为SegmentFault服务的,所以初始化的时候SegmentFault会把之前注册过的viewModel信息传给Scanner,便于它去扫描。
    }
    
    public scanBindDOM():object {} //找出attribute里带sf-,且等号右边表达式里含有viewModel的alias的Element,并返回一个view与viewModel的map

}

接下去,SegmentFault会获得Scanner.scanBindDOM()所返回的view_viewModel Map,来看看这个Map的具体数据结构

//template
{
    "vm_alias":[
        {
            "viewModel":viewModel,
            "element":element,
            "expression":expression,
            "attributeName":attributeName
        }
    ]
}
//如果实际中的DOM Tree是这样的,
<body>
    <p sf-text="userVM.username"></p>
    <input type="text" sf-value="userVM.username">
</body>
//那么,Scanner扫描到的结果应该是
{
    "userVM":[
        {
            "viewModel": userViewModel,
            "element": <p/>,
            "expression": "vm.username",
            "attributeName": "sf-text"
        },
        {
            "viewModel": userViewModel,
            "element": <input>,
            "expression": "vm.username",
            "attributeName": "sf-value"
        }
    ]
}

我的实现中特地定一个了一个BoundItem类来描述 {"viewModel":viewModel,"element":element,"expression":expression,"attributeName":attributeName}

//BoundItem.ts
export class BoundItem {
    public viewModel: object;
    public element: Element;
    public expression: string;
    public attributeName: string;
 
    constructor(viewModel: object, element: Element, expression: string, attributeName: string) {
        this.viewModel = viewModel;
        this.element = element;
        this.expression = expression;
        this.attributeName = attributeName;
    } 
}

拿到view_viewModel map后,SegmentFault会调用Renderer去挨个渲染每一个BoundItem。

export class Renderer{
    public render(boundItem:BoundItem) {};
}

好至此,几个主要的类都一一登场了,接下去我们完善下SegmentFault类,让ta和其它几个类联动起来

import {Scanner} from "./Scanner";
import {Watcher} from "./Watcher";
import {Renderer} from "./Renderer";
export let SegmentFault = class SegmentFault {
    private viewModelPool = {};
    private viewViewModelMap = {};
    private renderer = new Renderer();
    public init() {
        let scanner = new Scanner(this.viewModelPool);
        let watcher = new Watcher(this);
        //step 1, 暗中观察各个viewModel
        for (let key in this.viewModelPool) {
            watcher.observe(this.viewModelPool[key],this.viewModelChangedHandler);
        }
        /step 2 3, 扫描DOM Tree并返回Map 
        this.viewViewModelMap = scanner.scanBindDOM();
        //step 4, 渲染DOM
        Object.keys(this.viewViewModelMap).forEach(alias=>{
            this.refresh(alias);
        });   
    };
    public registerViewModel(alias:string, viewModel:object) {
        viewModel["_alias"] = alias;
        window[alias] = this.viewModelPool[alias] = viewModel;
    };
    public refresh(alias:string){
        let boundItems = this.viewViewModelMap[alias];
        boundItems.forEach(boundItem => {
            this.renderer.render(boundItem);
        });
    }
    private viewModelChangedHandler(viewModel,prop) {
        this.refresh(viewModel._alias);
    }
}

好,写到这里,骨架全部构建完成,你有没有兴趣自己花点时间去填充血肉呢?
我希望你能做到

这里贴出其它几个类的具体实现,仅供参考,你一定可以写得比我更好。

也放出github地址,上面有完整工程
github.com/momoko8443.…

以及在线演示地址
momoko8443.github.io/...

//Watcher.ts
export class Watcher {
    private sf;
    constructor(sf) {
        this.sf = sf;
    }
    public observe(viewModel, callback) {
        let host = this.sf;
        for (var key in viewModel) {
            var defaultValue = viewModel[key];
            (function (k, dv) {
                if (k !== "_alias") {
                    Object.defineProperty(viewModel, k, {
                        get: function () {
                            return dv;
                        },
                        set: function (value) {
                            dv = value;
                            console.log("do something after set a new value");
                            callback.call(host, viewModel, k);
                        }
                    });
                }
            })(key, defaultValue);
        }
    }
}
//Scanner.ts
import { BoundItem } from "./BoundItem";
export class Scanner {
    private prefix = "sf-";
    private viewModelPool;

    constructor(viewModelPool) {
        this.viewModelPool = viewModelPool;
    }
    public scanBindDOM() :object{
        let boundMap = {};
        
        let boundElements = this.getAllBoundElements(this.prefix);
        boundElements.forEach(element => {
           for (let i = 0; i < element.attributes.length; i++) {
                let attr = element.attributes[i];
                if (attr.nodeName.search(this.prefix) > -1) {
                    let attributeName = attr.nodeName;
                    let expression = element.getAttribute(attributeName);
                    for (let alias in this.viewModelPool) {
                        if (expression.search(alias + ".") != -1) {
                            let boundItem = new BoundItem(this.viewModelPool[alias], element, expression,attributeName);
                            if (!boundMap[alias]) {
                                boundMap[alias] = [boundItem];
                            } else {
                                boundMap[alias].push(boundItem);
                            }
                        }
                    }
                }
            }
        });  
        return boundMap;
    }

    private fuzzyFind(element:HTMLElement,text:string):HTMLElement {
        if (element && element.attributes) {
            for (let i = 0; i < element.attributes.length; i++) {
                let attr = element.attributes[i];
                if (attr.nodeName.search(text) > -1) {
                    return element;
                }
            }
        }
        return null;
    }
     private getAllBoundElements(prefix): Array<HTMLElement> {
        let elements = [];
        let allChildren = document.querySelectorAll("*");
        for (let i = 0; i < allChildren.length; i++) {
            let child: HTMLElement = allChildren[i] as HTMLElement;
            let matchElement = this.fuzzyFind(child, prefix);
            if (matchElement) {
                elements.push(matchElement);
            }
        }
        return elements;
    }
}
//BoundItem.ts
export class BoundItem {
    public viewModel: object;
    public element: Element;
    public expression: string;
    public attributeName: string;
    private interactiveDomConfig = {
        "INPUT":{
            "text":"input",
            "password":"input",
            "email":"input",
            "url":"input",
            "tel":"input",
            "radio":"change",
            "checkbox":"change",
            "color":"change",
            "date":"change",
            "datetime":"change",
            "datetime-local":"change",
            "month":"change",
            "number":"change",
            "range":"change",
            "search":"change",
            "time":"change",
            "week":"change",
            "button":"N/A",
            "submit":"N/A"
        },
        "SELECT":"change",
        "TEXTAREA":"change"
    }
    constructor(viewModel: object, element: Element, expression: string, attributeName: string) {
        this.viewModel = viewModel;
        this.element = element;
        this.expression = expression;
        this.attributeName = attributeName;
        this.addListener(this.element,this.expression);
    }

    private addListener(element,expression){
        let tagName = element.tagName;
        let eventName = this.interactiveDomConfig[tagName];
        if(!eventName){
            return;
        }
        if(typeof eventName === "object"){
            let type = element.getAttribute("type");
            eventName = eventName[type];
        }
        element.addEventListener(eventName, (e)=> {
            let newValue = (element as HTMLInputElement).value;
            let cmd = expression + "= \"" + newValue + "\"";
            try{
                eval(cmd);
            }catch(e){
                console.error(e);
            }
        });
    }
}
//Renderer.ts
import {BoundItem} from "./BoundItem";
export class Renderer{
    public render(boundItem:BoundItem) {
        var value = this.getValue(boundItem.viewModel, boundItem.expression);
        var attribute = boundItem.attributeName.split('-')[1];

        if (attribute.toLowerCase() === "innertext") {
            attribute = "innerText";
        }
        boundItem.element[attribute] = value;
    };
    private getValue(viewModel, expression) {
        return (function () {
            var alias = viewModel._alias;
            var tempScope = {};
            tempScope[alias] = viewModel;
            try {
                var pattern = new RegExp("\\b" + alias + "\\b", "gm");
                expression = expression.replace(pattern, "tempScope." + alias);
                var result = eval(expression);
                tempScope = null;
                return result;
            } catch (e) {
                throw e;
            }
        })();
    }
}

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