我怎么能在javascript中发表声明“for”等待

Question

I have 1 app using phone gap 2.5.0 wrote for ios. I am try to download files in server to my app. I need downloads a lot files (84 files); and i use 1 loop for to download all.

But when i use "for" statement, it's loop too fast and download all files almost at the same time, and some file can't download complete because timeout.

So I want 1 file download finish and then the next file begin download.

How can I do that?

Please help me! I am dumper...

This is my code:

var fileTransfer = new FileTransfer();

for (var i = 0; i < anhup.length; i++) {
    console.log("anhup[" + i + "]: " + anhup[i]);
    fileTransfer.download(
        "http://smartphone.thnt.vn/VietGames/GhepTranhTu/IOS/update/"
                + anhup[i], window.rootFS.fullPath + "/" + anhup[i],
        function(entry) {
            sa = entry.fullPath;
            console.log("download complete: " + entry.fullPath);

        }, function(error) {
            console.log("download error source " + error.source);
            console.log("download error target " + error.target);
            console.log("upload error code" + error.code);
        });
}

Answer 1

Try

function download() {
    var i = 0;

    var fileTransfer = new FileTransfer();

    function doDownload(i) {
        fileTransfer.download(
                "http://smartphone.thnt.vn/VietGames/GhepTranhTu/IOS/update/"
                        + anhup[i], window.rootFS.fullPath + "/" + anhup[i],
                function(entry) {
                    sa = entry.fullPath;
                    console.log("download complete: " + entry.fullPath);

                    if (i < anhup.length - 1) {
                        doDownload(i + 1);
                    }

                }, function(error) {
                    console.log("download error source " + error.source);
                    console.log("download error target " + error.target);
                    console.log("upload error code" + error.code);
                });
    }

    doDownload(0)
}

Answer 2

Make a function and keep calling itself until the object is empty, like so.

function loadFile() {
    // no more to load
    if(!anhup.length)
        return;

    var context = anhup.shift();

    fileTransfer.download(url, function(entry) {
        console.log("download complete: " + entry.fullPath);

        loadFile();
    }, function(error) {
        // ...
    });
}

Answer 3

You can't do that with "for" loop, you need to start downloading the next file when 'success' callback function is called; the easiest way is to make 'i' global variable, and rewrite your code like this (not tested!):

var i = 0;
var downloadNext;

var onSuccess = function(entry) {
    sa = entry.fullPath;
    console.log("download complete: " + entry.fullPath);
    i = i + 1;
    if (i < anhup.length) {
       downloadNext();
    }
};

var onFail = function(error) {
        console.log("download error source " + error.source);
        console.log("download error target " + error.target);
        console.log("upload error code" + error.code);
};

downloadNext = function() {
    console.log("anhup[" + i + "]: " + anhup[i]);
    fileTransfer.download(
        "http://smartphone.thnt.vn/VietGames/GhepTranhTu/IOS/update/"
            + anhup[i], window.rootFS.fullPath + "/" + anhup[i], 
         onSuccess,
         onFail
    );
};

// start downloading the first one
downloadNext();