xmlhttprequest在函数中无法正常工作

时间:2012-03-14 18:23:36

标签: php ajax html5 file-upload xmlhttprequest

有人知道为什么upload.onprogress在单独的函数上不能正常工作吗?

代码正常工作(进度条缓慢移动):

        xhr.upload.onprogress = function(e) {
            if (e.lengthComputable) {
                progress.value = (e.loaded / e.total) * 100;
            }
        };  

但是如果我把它付诸实践,它就不再起作用了:

xhr.upload.onprogress = uploadProgress(event);

function uploadProgress(e) {
    if (e.lengthComputable) {
        progress.value = (e.loaded / e.total) * 100;
    }
}   

在第二个代码上,进度条在文件完成上传后直接跳转到100%而不是,在上传过程中很好地移动到100%


所以,我已经尝试了所提供的解决方案,如果我将函数放入其中,它实际上是可行的。有没有办法把它放在功能之外?

        function uploadFile(blobFile, fileName) {
            ...
            ...

            // Listen to the upload progress for each upload.
            xhr.upload.onprogress = uploadProgress;

            // Progress Bar Calculation why it has to be in uploadFile function..
            function uploadProgress(e) {
                if (e.lengthComputable) {
                    progress.value = (e.loaded / e.total) * 100;
                }
            }                            

            uploaders.push(xhr);
            xhr.send(fd);
        }  

        //it does not work if I put it outside the function. is there anyway to do this?  
        function uploadProgress(e) {
             if (e.lengthComputable) {
                 progress.value = (e.loaded / e.total) * 100;
             }
        }   

3 个答案:

答案 0 :(得分:6)

使用uploadProgress(event);调用函数本身并将返回值赋给xhr.upload.onprogress,而不是将其指定为回调函数:

xhr.upload.onprogress = uploadProgress;

答案 1 :(得分:1)

在第二个例子中,你应该使用

xhr.upload.onprogress = uploadProgress;

xhr.upload.onprogress = uploadProgress(event);

您已分配调用函数的结果,而不是对函数的引用。

答案 2 :(得分:1)

在分配回调之前如何定义函数? JavasCript有时在以后定义函数时会遇到问题。

我的意思是你可以替换:

// Listen to the upload progress for each upload.
xhr.upload.onprogress = uploadProgress;

// Progress Bar Calculation
function uploadProgress(e) {
    if (e.lengthComputable) {
         progress.value = (e.loaded / e.total) * 100;
    }
}

// Progress Bar Calculation
function uploadProgress(e) {
    if (e.lengthComputable) {
         progress.value = (e.loaded / e.total) * 100;
    }
}
// Listen to the upload progress for each upload.
xhr.upload.onprogress = uploadProgress;