phonecap同步调用文件系统 [英] phonecap synchronous call to filesystem

问题描述

我在使用phonegap进行异步调用时遇到问题，因为我需要获取以下函数的返回值才能处理其余代码.

I encounter a problem with asynchronous call using phonegap, because I need to get the return of the following function in order to process the rest of the code.

所以我有以下功能:

function getFileContent(fileName) {
    var content = null;
    document.addEventListener("deviceready", function() {
        window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, function(fileSystem) {
            fileSystem.root.getFile("data/" + fileName, null, function(fileEntry) {
                fileEntry.file(function(file) {
                    var reader = new FileReader();
                    reader.onloadend = function(evt) {
                        content = evt.target.result;
                        alert(content);
                    }
                    reader.readAsText(file);
                });
            }, fail);
        }, fail);
    }, false);
   return content;
}

但是当我先尝试alert(getFileContent(fileName));时，我会得到null，然后是带有文件内容的警报

but when I try alert(getFileContent(fileName)); first I get null and then the alert with the content of the file

我尝试在返回之前添加以下行，但是什么也不执行:

I have try to add the following line before the return but then nothing is executed:

while (content == null);

我想避免使用setTimeout之类的东西，因为我需要立即获得响应，而无需延迟

I would like to avoid using something like setTimeout because I need to get the response immediately and not after a delay

推荐答案

正如SHANK所说，我必须在最后一个回调函数中调用final函数，因此我只是将函数更改为:

As said by SHANK I must call the final function in the last callback function so I just changed my function to:

function getFileContent(fileName, call) {
    var callBack = call;
    var content = null;
    var args = arguments;
    var context = this;
    document.addEventListener("deviceready", function() {
        window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, function(
                fileSystem) {
            fileSystem.root.getFile("data/" + fileName, null, function(
                    fileEntry) {
                fileEntry.file(function(file) {
                    var reader = new FileReader();
                    reader.onloadend = function(evt) {
                        args = [].splice.call(args, 0);
                        args[0] = evt.target.result;
                        args.splice(1, 1);
                        callBack.apply(context, args);
                    }
                    reader.readAsText(file);
                });
            }, fail);
        }, fail);
    }, false);
}

现在可以正常工作了

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