Extjs上传图片预览与解决无法预览

{
               width: 450,
               fileUpload: true,
               fieldLabel: '选择图片',
               items: [{
                   xtype: 'textfield',
                   id: 'up_forth',
                   name: 'up_forth',
                   inputType: 'file',
                   width: 300
               }]
}

预览box

{
                   columnWidth: .18,
                   bodyStyle: ' margin:4px 10px 10px 5px',
                   layout: 'form',
                   items: [{
                       xtype: 'box',
                       autoEl: {
                           width: 150, height: 150,
                           tag: 'div',
                           id: 'browser_up_forth'
                       }
                   }]
}

var preview = function (myform, control_id) {
    var img_reg = /.([jJ][pP][gG]){1}$|.([jJ][pP][eE][gG]){1}$|.([gG][iI][fF]){1}$|.([pP][nN][gG]){1}$|.([bB][mM][pP]){1}$/
    myform.on('render', function (f) {
        myform.form.findField(control_id).on('render', function () {
            Ext.get(control_id).on('change', function (field, newValue, oldValue) {
                var obj = Ext.get(control_id).dom;
                var url = getFullPath(obj);
                if (img_reg.test(url)) {
                    var newPreview = Ext.get('browser_' + control_id).dom;
                    var showPic = Ext.get("showPic_" + control_id);
                    if (showPic != null) {
                        showPic.remove();//删除原来的图片
                    }
                    var imgDiv = document.createElement("div");
                    imgDiv.id = "showPic_" + control_id;
                    document.body.appendChild(imgDiv);
                    imgDiv.style.width = "150px";
                    imgDiv.style.height = "150px";
                    imgDiv.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod = scale)";
                    imgDiv.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = url;
                    newPreview.appendChild(imgDiv);
                }
            }, this);
        }, this);
    }, this);
}

//得到图片地址
function getFullPath(obj) {
    if (obj) {
        // ie
        if (window.navigator.userAgent.indexOf("MSIE") >= 1) {
            obj.select();
            return document.selection.createRange().text;
        }
        // firefox
        else if (window.navigator.userAgent.indexOf("Firefox") >= 1) {
            if (obj.files) {
                return obj.files.item(0).getAsDataURL();
            }
            return obj.value;
        }
        return obj.value;
    }
}