Quickstart: Roaming application data (Windows Store apps using JavaScript and HTML) (Windows)

Language: JavaScript and HTML | VB/C#/C++ and XAML

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Learn about storing and retrieving settings and files from the roaming application data store. For info about the roaming application data store and why you'd want to use it, see Roaming application data.

Register to receive notification when roaming data changes

This example sets datachangeHandler as the handler for roaming data changes.

JavaScript



var applicationData = Windows.Storage.ApplicationData.current;
 
function initialize() 
{
    applicationData.addEventListener("datachanged", datachangeHandler);
}

function dataChangeHandler(eventArgs)
{
    // TODO: Refresh your data
}

Get the containers for the app's settings and files

Use the ApplicationData.roamingSettings property to get the settings and the ApplicationData.roamingFolder property to get the files.

JavaScript


var roamingSettings = applicationData.roamingSettings;
var roamingFolder = applicationData.roamingFolder;

The next steps use the roamingSettings and roamingFolder variables from this step.

Write data to a setting

Use the ApplicationDataContainer.values property to access the settings in the roamingSettings container we got in the previous step. This example creates a setting named exampleSetting exampleSetting and a HighPriority setting that is best suited for transitioning time-critical information such as application state.

JavaScript


// Simple setting

roamingSettings.values["exampleSetting"] = "Hello World";
// High Priority setting, for example, last page position in book reader app

roamingSettings.values["HighPriority"] = "65";

An ApplicationDataCompositeValue object contains settings that must be accessed atomically. This example creates a composite setting named exampleCompositeSetting and adds it to the roamingSettings container.

JavaScript


// Composite setting

var composite = new Windows.Storage.ApplicationDataCompositeValue();
composite["intVal"] = 1;
composite["strVal"] = "string";

roamingSettings.values["exampleCompositeSetting"] = composite;

Call the ApplicationDataContainer.CreateContainer method to create a settings container. This example creates a settings container named exampleContainer and adds a setting named exampleSetting. The Always value from the ApplicationDataCreateDisposition enumeration indicates that the container should be created if it does not already exist.

After changing a setting in the roaming app data store, the system sends the datachanged event.

JavaScript


// Setting in a container

var container = roamingSettings.createContainer("exampleContainer", 
                                                Windows.Storage.ApplicationDataCreateDisposition.Always);

if (roamingSettings.containers.hasKey("exampleContainer"))
{
    roamingSettings.containers.lookup("exampleContainer").values["exampleSetting"] = "Hello World";
}

Read data from a setting

Use the ApplicationDataContainer.values property to access the exampleSetting setting in the roamingSettings container.

JavaScript


// Simple setting

var value = roamingSettings.values["exampleSetting"];
        
if (!value)
{
    // No data
}
else
{
    // Access data in value
}

Use the ApplicationDataContainer.values property to access the exampleCompositeSetting setting in the roamingSettings container.

JavaScript


// Composite setting

var composite = roamingSettings.values["exampleCompositeSetting"];

if (!composite)
{
    // No data
}
else
{
    // Access data in composite["intVal"] and composite["strVal"]
}

Use the ApplicationDataContainer.values property to access the exampleSetting setting in the exampleContainer container.

JavaScript


// Setting in a container

var hasContainer = roamingSettings.containers.hasKey("exampleContainer");

if (hasContainer)
{
    // Access data in roamingSettings.containers.lookup("exampleContainer").values.hasKey("exampleSetting");
}

Write data to a file

Use the file APIs, such as Windows.Storage.StorageFolder.createFileAsync and Windows.Storage.FileIO.writeTextAsync, to create and update a file in the roaming app data store. This example creates a file named dataFile.txt in the roamingFolder container and writes the current date and time to the file. The replaceExisting value from the CreationCollisionOption enumeration indicates that the file should be replaced if it already exists.

JavaScript


function writeTimestamp() {
   roamingFolder.createFileAsync("dataFile.txt", Windows.Storage.CreationCollisionOption.replaceExisting)
      .then(function (sampleFile) {
         var formatter = new Windows.Globalization.DateTimeFormatting.DateTimeFormatter("longtime");
         var timestamp = formatter.format(new Date());

         return Windows.Storage.FileIO.writeTextAsync(sampleFile, timestamp);
      }).done(function () {      
      });
}

Read data from a file

Use the file APIs, such as Windows.Storage.StorageFolder.getFileAsync, Windows.Storage.StorageFile.GetFileFromApplicationUriAsync and Windows.Storage.FileIO.readTextAsync to open and read a file in the roaming app data store. This example opens the dataFile.txt file created in the previous step and reads the date from the file. The openIfExists value from the CreationCollisionOption enumeration indicates that the file must exist. For details on loading file resources from various locations see How to load file resources.

JavaScript


function readTimestamp() {
   roamingFolder.getFileAsync("dataFile.txt")
      .then(function (sampleFile) {
         return Windows.Storage.FileIO.readTextAsync(sampleFile);
      }).done(function (timestamp) {
         // Data is contained in timestamp
      }, function () {
         // Timestamp not found
      });
}

Delete settings when finished with them

Call the ApplicationDataContainerSettings.remove method to delete the exampleSetting setting from the roamingSettings container when you have finished with it.

JavaScript


// Simple setting

roamingSettings.values.remove("exampleSetting");

Call the ApplicationDataCompositeValue.remove method to delete the exampleCompositeSetting composite setting from the roamingSettings container when you have finished with it.

JavaScript


// Delete composite setting

roamingSettings.values.remove("exampleCompositeSetting");

Call the ApplicationDataContainer.deleteContainer method to delete the exampleContainer settings container when you have finished with it.

JavaScript


// Delete container

roamingSettings.deleteContainer("exampleContainer");

Remarks

Each app has a quota for roaming application data. Check the ApplicationData.roamingStorageQuota property to determine the total size of roaming data allowed. If your roaming data exceeds the quota, it won’t roam until its size is less than the quota again.

Quickstart: Roaming application data (Windows Store apps using JavaScript and HTML)

Register to receive notification when roaming data changes

Get the containers for the app's settings and files

Write data to a setting

Read data from a setting

Write data to a file

Read data from a file

Delete settings when finished with them

Remarks

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