为什么progressEvent.total在phonegap中返回-1

Question

我试图下载多个文件。文件在我的设备中正常下载。但progressEvent给出了一些奇怪的结果。对于所有情况progressEvent.total返回-1。虽然progressEvent.loaded值总是在变化。 如何解决它。

function downloadFile(remoteUrl, localPath) {
    var fileTransfer = new FileTransfer();

    fileTransfer.onprogress = function(progressEvent) {
        if (progressEvent.lengthComputable) {
            var perc = Math.floor(progressEvent.loaded / progressEvent.total * 100);
            //statusDom.innerHTML = perc + "% loaded...";
            statusDom.innerHTML = progressEvent.loaded + " - " + progressEvent.total;
        } else {
            if(statusDom.innerHTML == "") {
                statusDom.innerHTML = "Loading";
            } else {
                statusDom.innerHTML += ".";
            }
        }
    };

    fileTransfer.download(encodeURI(remoteUrl), localPath, function(e) {}, fail);
}