javascript - 如何检查 observableArray 的变化

Question

我正在使用 knockout_2.0.js。我有一个 observableArray，我在其上设置了订阅。喜欢 ：

 var Items = ko.observableArray();


 Items.subscribe(function(newValue){

  //I want to check here whether the item is Added or Deleted from the array

 }); 

我怎样才能做到这一点 ？

Answer 1

如果您只想知道是否添加或删除了某些内容，您可以使用外部作用域上的变量轻松跟踪它。

var items = ko.observableArray();

var itemLen = items.length;

items.subscribe(function (newValue) {

    //I want to check here whether the item is Added or Deleted from the array
    if (itemLen > items.length) {
        // Item removed
    } else if (itemLen < items.length) {
        // item added
    } else {
        // something else was modified
    }
    itemLen = items.length;
});

Answer 2

试试下面的代码，这可能会有所帮助。

var Items = ko.observableArray();
var ItemsLength = ko.observableArray();

this.ItemsLength = ko.computed({
    read: function() {
    return this.Items().length;
    }
});

this.ItemsLength.subscribe(function(newValue){

  //you will get control over here whether the
       item is Added or Deleted from the array

});