Question

我被困在Javascript的事件处理程序方面。

rowCells [j]是对唯一对象的引用。 galleryCell也是对新创建对象的引用。按理说这两者可以联系在一起。

但是，似乎两个引用完全没有绑定在一起，以使事件侦听器正常工作。所有单元格都被分配给相同的东西（最后一个galleryCell对象）。

galleryCell变量位于for循环中，在每次迭代时获取一个新引用。为什么这些引用会丢失？

function TypeGallery (galleryObj)
{  //receives the <div> element that contains rows and cells of a gallery

   //Properties --------------
   var galleryCellArr = [];   //array of galleryZoomCell objects

   //Methods -----------------  
   var Initialize  = function ()
   {
      var rows     = galleryObj.children;
      var rowCount = rows.length;
      for (var i=0;i<rowCount;i++)
      {
         var rowCells     = rows[i].children;
         var rowCellCount = rowCells.length;
         for (var j=0;j<rowCellCount;j++)
         {
            var sliderObj   = new TypeSlider(300,1,false);
            var galleryCell = new TypeGalleryZoomCell(rowCells[j],sliderObj)
            galleryCellArr.push(galleryCell);

            rowCells[j].onmousedown = function () {galleryCell.Deploy();};
            rowCells[j].onmouseup   = function () {galleryCell.Retract();};
         }
      }
   }

   //Initialization
   Initialize();
}

Answer 1

尝试将javascript闭包放在for循环中，如下所示：

function TypeGallery (galleryObj)
{  //receives the <div> element that contains rows and cells of a gallery

   //Properties --------------
   var galleryCellArr = [];   //array of galleryZoomCell objects

   //Methods -----------------  
   var Initialize  = function ()
   {
      var rows     = galleryObj.children;
      var rowCount = rows.length;
      for (var i=0;i<rowCount;i++)
      {
         var rowCells     = rows[i].children;
         var rowCellCount = rowCells.length;
         for (var j=0;j<rowCellCount;j++)
         {
            (function(j) {

                var sliderObj   = new TypeSlider(300,1,false);
                var galleryCell = new TypeGalleryZoomCell(rowCells[j],sliderObj)
                galleryCellArr.push(galleryCell);

                rowCells[j].onmousedown = function () {galleryCell.Deploy();};
                rowCells[j].onmouseup   = function () {galleryCell.Retract();};

            })(j);
         }
      }
   }

   //Initialization
   Initialize();
}

Answer 2

好的，我现在了解Javascript和块范围限制的问题。

在此过程中我发现了第二个可能的解决方案：是否有任何异议或警告用'让'替换'var' for for循环？
就我所知，这段代码很好用。有任何隐患吗？

   var Initialize  = function ()
   {
      var rowsArr  = galleryObj.children;
      var rowCount = rowsArr.length;
      for (let i=0;i<rowCount;i++)
      {  //Javascript does not understand block-scope unless the let keyword
         let rowCellsArr  = rowsArr[i].children;
         let rowCellCount = rowCellsArr.length;
         for (let j=0;j<rowCellCount;j++) 
         {
            //Attach (rowCellsArr[j]);

            let sliderObj   = new TypeSlider(300,1,false);
            let galleryCell = new TypeGalleryZoomCell(rowCellsArr[j],sliderObj);
            galleryCellArr.push(galleryCell); 

            galleryCellArr[galleryCellArr.length-1].cell.onmousedown = function () {galleryCell.Deploy();};
            galleryCellArr[galleryCellArr.length-1].cell.onmouseup   = function () {galleryCell.Retract();};

         }
      }
   }

Javascript：将自定义对象方法绑定到事件侦听器

2 个答案: