Android studio，重新打开应用后删除了File.properties

Question

I saved a File.properties in this.getFilesDir() + "Data.propertie" . In the app, I save the data that the user wrote, but when i open the app, all the data (or the file) that I saves from the previous time has been deleted.

Example:

        // Store
        for (Map.Entry<String,String> entry : MainActivity.Notes.entrySet()) { // Put all data from Notes in properties to store later
            properties.put(entry.getKey(), entry.getValue());
        }

        try { properties.store(new FileOutputStream(this.getFilesDir() + "data.properties"), null); } // Store the data
        catch (IOException e) { e.printStackTrace(); } // Error exception

        // Load the map
        Properties properties = new Properties(); // Crate properties object to store the data


        try {
            properties.load(new FileInputStream(this.getFilesDir() + "data.proprties")); } // Try to load the map from the file
        catch (IOException e) { e.printStackTrace(); } // Error exception

        for (String key : properties.stringPropertyNames()) {
            Notes.put(key, properties.get(key).toString()); // Put all data from properties in the Notes map
        }

// Can load the data

You can see that i saved the data in the file, and I can load it, but when I open the app, the data has been deleted

There is a way to write in the file and save the data that i write to the next time I open the app?

Answer 1

First off Context.getFilesDir returns a File object. This File represents the private data directory of your app.

Then you do getFilesDir() + "foo" which will implicitly call toString() on the File instance. File.toString() is equivalent to File.getPath which does not necessarily return a trailing slash.

This means, if getFilesDir() returns a File at /data/app , your properties file will become /data/appdata.properties which is not in your data Folder and cannot be written to.

Instead, to get a File within a directory you can create a new File instance with that directory. eg:

File propertiesFile = new File(this.getFilesDir(), "data.properties");
// use propertiesFile for FileOutputStream/FileInputStream etc.

This ensures that your properties file is within that directory and prevents any issues from file separators