knockout.js的学习笔记3
上一节主要是说viewModel各个域中相互通知，本节开始介绍viewModel与节点的相互通知。
我们在body上添加如下HTML片断：
The name is <span data-bind="text: fullName" id="node"></span>
然后将第一节提到的$.applyBindings疯狂删减到这样：
$.applyBindings = function(model, node){
var str = node.getAttribute("data-bind");
str = "{"+str+"}"
var bindings = eval("0,"+str);
for(var key in bindings){//如果直接eval肯定会报错,因为它找到fullName
console.log(key)
}
}
window.onload = function(){
var model = new MyViewModel();
var node = document.getElementById("node");
$.applyBindings(model, node)
}
意料中的失败，因为fullName在window中找不到。knockoutjs里面有一个叫buildEvalWithinScopeFunction处理此问题：
$.buildEvalWithinScopeFunction = function (expression, scopeLevels) {
var functionBody = "return (" + expression + ")";
for (var i = 0; i < scopeLevels; i++) {
functionBody = "with(sc[" + i + "]) { " + functionBody + " } ";
}
return new Function("sc", functionBody);
}
然后将applyBindings 改成这样:
$.applyBindings = function(model, node){
var str = node.getAttribute("data-bind");
str = "{"+str+"}"
var fn = $.buildEvalWithinScopeFunction(str,2);
var bindings = fn([node,model])
console.log(bindings.text == model.fullName)//到这里我们就把viewModel与节点关联起来了
}
在data-bind定义两个东西,一个是viewModel中的域，另一个是对应的操作，在这里是text！在knockout中有一个叫ko.bindingHandlers的对象，里面储放着各种操作，格式如下：
ko.bindingHandlers['event'] = {
'init' : function (element, valueAccessor, allBindingsAccessor, viewModel) { }
};
ko.bindingHandlers['submit'] = {
'init': function (element, valueAccessor, allBindingsAccessor, viewModel) { }
};
ko.bindingHandlers['visible'] = {
'update': function (element, valueAccessor) { }
}
ko.bindingHandlers['enable'] = {
'update': function (element, valueAccessor) { }
};
ko.bindingHandlers['disable'] = {
'update': function (element, valueAccessor) { }
};
ko.bindingHandlers['value'] = {
'init': function (element, valueAccessor, allBindingsAccessor) { },
'update': function (element, valueAccessor) { }
};
ko.bindingHandlers['options'] = {
'update': function (element, valueAccessor, allBindingsAccessor) { }
};
ko.bindingHandlers['selectedOptions'] = {
'init': function (element, valueAccessor, allBindingsAccessor) { },
'update': function (element, valueAccessor) { }
};
ko.bindingHandlers['text'] = {
'update': function (element, valueAccessor) {
ko.utils.setTextContent(element, valueAccessor());
}
};
ko.bindingHandlers['html'] = {
'init': function() {
return { 'controlsDescendantBindings': true };
},
'update': function (element, valueAccessor) {
var value = ko.utils.unwrapObservable(valueAccessor());
ko.utils.setHtml(element, value);
}
};
init可以猜测是用于第一次绑定元素时调用的，update是每次viewModel调用的。
现在我们是玩玩，不用大动干戈。
$.applyBindings = function(model, node){
var str = node.getAttribute("data-bind");
str = "{"+str+"}"
var fn = $.buildEvalWithinScopeFunction(str,2);
var bindings = fn([node,model]);
for(var key in bindings){
if(bindings.hasOwnProperty(key)){
var fn = $.bindingHandlers["text"]["update"];
fn(node,bindings[key])
}
}
}
$.bindingHandlers = {}
$.bindingHandlers["text"] = {
'update': function (node, observable) {
var val = observable()
val = val == null ? "" : val+"";
if("textContent" in node){//优先考虑标准属性textContent
node.textContent = val;
}else{
node.innerText = val;
}
//处理IE9的渲染BUG
if (document.documentMode == 9) {
node.style.display = node.style.display;
}
}
}
window.onload = function(){
var model = new MyViewModel();
var node = document.getElementById("node");
$.applyBindings(model, node);
}
到这里，我们就可以把Planet Earth正确地显示在span中，但当viewModel中的FullName发生改变时，span并没有发生改变，缘由是我们没有把它们绑在一起。很简单，我们把$.applyBindings里面的逻辑都整进一个$.computed 中就行了。
var validValueType = $.oneObject("Null,NaN,Undefined,Boolean,Number,String")
$.dependencyDetection = (function () {
var _frames = [];
return {
begin: function (ret) {
_frames.push(ret);
},
end: function () {
_frames.pop();
},
collect: function (self) {
if (_frames.length > 0) {
self.list = self.list || [];
var fn = _frames[_frames.length - 1];
if ( self.list.indexOf( fn ) >= 0)
return;
self.list.push(fn);
}
}
};
})();
$.valueWillMutate = function(observable){
var list = observable.list
if($.type(list,"Array")){
for(var i = 0, el; el = list[i++];){
el();
}
}
}
$.observable = function(value){
var v = value;//将上一次的传参保存到v中,ret与它构成闭包
function ret(neo){
if(arguments.length){ //setter
if(!validValueType[$.type(neo)]){
$.error("arguments must be primitive type!")
return ret
}
if(v !== neo ){
v = neo;
$.valueWillMutate(ret);//向依赖者发送通知
}
return ret;
}else{ //getter
$.dependencyDetection.collect(ret);//收集被依赖者
return v;
}
}
value = validValueType[$.type(value)] ? value : void 0;
ret(arguments[0]);//必须先执行一次
return ret
}
$.computed = function(obj, scope){//为一个惰性函数，会重写自身
//computed是由多个$.observable组成
var getter, setter
if(typeof obj == "function"){
getter = obj
}else if(obj && typeof obj == "object"){
getter = obj.getter;
setter = obj.setter;
scope = obj.scope;
}
var v
var ret = function(neo){
if(arguments.length ){
if(typeof setter == "function"){//setter不一定存在的
if(!validValueType[$.type(neo)]){
$.error("arguments must be primitive type!")
return ret
}
if(v !== neo ){
setter.call(scope, neo);
v = neo;
$.valueWillMutate(ret);//向依赖者发送通知
}
}
return ret;
}else{
$.dependencyDetection.begin(ret);//让其依赖知道自己的存在
v = getter.call(scope);
$.dependencyDetection.end();
return v;
}
}
ret(); //必须先执行一次
return ret;
}
function MyViewModel() {
this.firstName = $.observable('Planet');
this.lastName = $.observable('Earth');
this.fullName = $.computed({
getter: function () {
return this.firstName() + " " + this.lastName();
},
setter: function (value) {
var lastSpacePos = value.lastIndexOf(" ");
if (lastSpacePos > 0) { // Ignore values with no space character
this.firstName(value.substring(0, lastSpacePos)); // Update "firstName"
this.lastName(value.substring(lastSpacePos + 1)); // Update "lastName"
}
},
scope: this
});
}
$.buildEvalWithinScopeFunction = function (expression, scopeLevels) {
var functionBody = "return (" + expression + ")";
for (var i = 0; i < scopeLevels; i++) {
functionBody = "with(sc[" + i + "]) { " + functionBody + " } ";
}
return new Function("sc", functionBody);
}
$.applyBindings = function(model, node){
var nodeBind = $.computed(function (){
var str = "{" + node.getAttribute("data-bind")+"}"
var fn = $.buildEvalWithinScopeFunction(str,2);
var bindings = fn([node,model]);
for(var key in bindings){
if(bindings.hasOwnProperty(key)){
var fn = $.bindingHandlers["text"]["update"];
var observable = bindings[key]
$.dependencyDetection.collect(observable);//绑定viewModel与UI
fn(node, observable)
}
}
},node);
return nodeBind
}
$.bindingHandlers = {}
$.bindingHandlers["text"] = {
'update': function (node, observable) {
var val = observable()
val = val == null ? "" : val+"";
if("textContent" in node){//优先考虑标准属性textContent
node.textContent = val;
}else{
node.innerText = val;
}
//处理IE9的渲染BUG
if (document.documentMode == 9) {
node.style.display = node.style.display;
}
}
}
window.onload = function(){
var model = new MyViewModel();
var node = document.getElementById("node");
var nodeBind = $.applyBindings(model, node);
$.log("+++++++++++++++++++++++++++")
$.log(model.fullName.list[0] == nodeBind);
$.log(model.lastName.list[0] == model.fullName);
$.log(model.firstName.list[0] == model.fullName);
// $.log(model.lastName.list[0] == model.fullName)
setTimeout(function(){
model.fullName("xxx yyy")
},1500)
setTimeout(function(){
model.fullName("111 222")
},3000)
}
大家可以下载回来看看效果：点我