科尔多瓦文件检查异步写入

Question

I use cordovaFile method to test if file exists in several directories. When I find one, I do some actions and break the for loop.

But, cordovaFile.checkFile (like writeFile or others methods) works asynchronously, so the CLI displays me (for console.log) :

1     890383   log      ===== file_created =====
2     890389   log      object
3     890395   log      null
5     890492   log      ===== file_created =====
6     890494   log      object
7     890496   log      null
9     890556   log      ===== file_created =====
10    890558   log      object
11    890559   log      null
13    890626   log      ===== file_created =====
14    890627   log      object
15    890628   log      null
17    890671   log      ===== file_created =====
18    890672   log      object
19    890674   log      null

Is there a way to run cordova.checkFile synchronously ?

My code (originnaly in controllers) :

dir_list = [
    cordova.file.applicationDirectory,
    cordova.file.externalRootDirectory,
    cordova.file.externalDataDirectory,
    cordova.file.applicationStorageDirectory,
    cordova.file.dataDirectory
];

for (index = 0; index < dir_list.length; ++index) {
    current_dir = dir_list[index];

    file_created = null;
    $cordovaFile.checkFile(current_dir, filename)
    .then(function (success) {
        file_created = true;
    }, function (error) {
        file_created = false;
    }

    console.log('===== file_created =====');
    console.log(typeof file_created);
    console.log(JSON.stringify(file_created));

    if (file_created) {
        // Some actions
        break;
    }
});

Solution inspired by Aaron Franco's answer

// This function will run by backup function
$scope.write_file_list = function(file_list, filename, content) {
  if (file_list.length) {
    current_dir = file_list[0];
    $cordovaFile.writeFile(current_dir, filename, content, true).then(
    function(result) {
      // Action if file saved
    }, function(err) {
      file_list.splice(0, 1);
      $scope.write_file_list(file_list, filename, content);
    });
  }
  else {
    // Action if none file saved
  }

};

// This function is called by controller
$scope.backup = function() {
    dir_list = [
        cordova.file.applicationDirectory,
        cordova.file.externalRootDirectory,
        cordova.file.externalDataDirectory,
        cordova.file.applicationStorageDirectory,
        cordova.file.dataDirectory
    ];
    content = 'content file';
    filename = 'test.txt';
    $scope.write_file_list(dir_list, filename, content);
}

Answer 1

You should execute your code inside a method that can be called after the file is created.

dir_list = [
    cordova.file.applicationDirectory,
    cordova.file.externalRootDirectory,
    cordova.file.externalDataDirectory,
    cordova.file.applicationStorageDirectory,
    cordova.file.dataDirectory
];

for (index = 0; index < dir_list.length; ++index) {
    current_dir = dir_list[index];
    $cordovaFile.checkFile(current_dir, filename)
    .then(function (success) {
        console.log('===== file_created =====');
        // do some stuff here that deals with the created file.
    }, function (error) {
        // do something with error
    }

});

By doing it this way, there is no need to flag the file creation. You know the file was created when your success function is called.

Cordova is designed to run on the main thread of your application, so anything you do synchronously will block that thread. This is why Cordova apps are written asynchronously. That and the fact that JavaScript is an Async language to begin with.

The alternative would be to use a promise.

<script src="https://www.promisejs.org/polyfills/promise-7.0.4.min.js"></script>

You should be able to use it in this way to check one file.

dir_list = [
    cordova.file.applicationDirectory,
    cordova.file.externalRootDirectory,
    cordova.file.externalDataDirectory,
    cordova.file.applicationStorageDirectory,
    cordova.file.dataDirectory
];
function checkIfFileExist(filename) {
   return new Promise(function(resolve, reject){
     for (index = 0; index < dir_list.length; ++index) {
       current_dir = dir_list[index];
       $cordovaFile.checkFile(current_dir, filename).then(resolve, reject);
     }
   });
 }

checkIfFileExist(filename).then(function (successData) { 
    // file exists here
}, function (err) { 
    // file doesn't exist here
});

That should allow you to check one at a time. For more details on using promises:

http://ramkulkarni.com/blog/using-javascript-promises-with-cordova/