Load file from assets android

Assets (Активы)

В Android имеется ещё один каталог, в котором могут храниться файлы, предназначенные для включения в пакет — assets. Этот каталог находится на том же уровне, что и res. Для файлов, располагающихся в assets, в R.java не генерируются идентификаторы ресурсов. Для их считывания необходимо указать путь к файлу. Путь к файлу является относительным и начинается с /assets. Этот каталог, в отличие от подкаталога res, позволяет задавать произвольную глубину подкаталогов и произвольные имена файлов и подкаталогов.

По умолчанию проект в студии не содержит данную папку. Чтобы её создать, выберите меню File | New | Folder | Assets Folder.

Чтение файлов

Для доступа к файлам используется класс AssetManager. Пример для чтения текстового файла.

Сначала на Kotlin.

Для доступа к графическому файлу из актива можно использовать следующий код:

Вы также можете загрузить изображение в Bitmap, используя BitmapFactory.decodeStream(), вместо Drawable.

Функция-расширение для Kotlin, которая вернёт Bitmap.

Используем собственные шрифты

Напишем практический пример создания приложения, в котором будут использоваться собственные шрифты, не входящие в стандартную библиотеку шрифтов Android. Для этого мы упакуем нужные шрифты вместе с приложением. Поместим в каталог assets/fonts файлы шрифтов (можно скачать бесплатные шрифты с сайтов 1001 Free Fonts или Urban Fonts ).

В файл разметки добавим пару текстовых полей с заготовленным текстом для вывода этого текста с нашим шрифтом.

В классе активности загрузим объект EditText из ресурсов, а затем создадим объект Typeface, используя вызов статического метода Typeface.createFromAsset(). Метод createFromAsset() принимает два параметра:

• объект AssetManager, который можно получить вызовом метода getAssets()
• путь к файлу актива.

Например, загрузить шрифт для текстового поля EditText можно следующим способом:

Запустив проект, мы увидим в текстовых полях надписи Happy New Year! и Meow!, выводимые нашими собственными шрифтами.

Пример для фрагмента.

Загрузка локальных файлов из активов в WebView

Если нужно загрузить локальные страницы и изображения из активов в WebView, то можно использовать префикс file://android_asset. Подробнее смотрите в статье про WebView.

Получаем список файлов в папке assets

Можно получить список файлов, которые находятся в папке assets. Для быстрой проверки кода я вручную скопировал в папку два файла:

Кроме ваших файлов, также возвращаются странные папки /images, /sounds, /webkit. Учитывайте это в своих проектах. Так как в папке можно создавать собственные подпапки, то можно воспользоваться вспомогательным методом:

Ограничение на размер файлов

По сети гуляет информация, что существует ограничение в 1 Мб на размер файлов в папке assets. При превышении размера у вас может появиться ошибка:

Я не сталкивался, поэтому рецепт решения проблемы не предлагаю.

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Game Programming, Android and Retro Games

Android: Loading files from the Assets and Raw folders

Posted by Dimitri | May 24th, 2011 | Filed under Programming

This tutorial will explain how to load files from the res/raw and the Assets folder using a String to specify the file name. Yes, there are a lot of tutorials on this subject, but they all use the automatically generated integer IDs from the R class as inputs and not many of them even mention the possibility of loading files from the Assets folder. As a result of depending on the ID, the file reference must be known beforehand.

Instead, the code featured in this post will explain how to find the reference to the file and then load it at runtime based solely on its name. This means that the reference ID and the file don’t even have to exist in the first place, and can be acquired at run time.

Before looking into the code, it’s important to highlight the main differences between the raw folder and the Assets folder. Since raw is a subfolder of Resources (res), Android will automatically generate an ID for any file located inside it. This ID is then stored an the R class that will act as a reference to a file, meaning it can be easily accessed from other Android classes and methods and even in Android XML files. Using the automatically generated ID is the fastest way to have access to a file in Android.

The Assets folder is an “appendix” directory. The R class does not generate IDs for the files placed there, so its less compatible with some Android classes and methods. Also, it’s much slower to access a file inside it, since you will need to get a handle to it based on a String. There is also a 1MB size limit for files placed inside the Assets folder, however some operations are more easily done by placing files in this folder, like copying a database file to the system’s memory. There’s no (easy) way to create an Android XML reference to files inside the Assets folder.

The first thing the code does is to create two private variables. A Resources object that will act as a handle to the app’s resources and a String, that will be used to output the content of the files to LogCat (lines 16 and 18).

Now let’s jump straight to line 60 where the LoadFile() method is defined. It returns a String and takes two parameters: the first one is the file name and the second is a boolean, that signals the method whether it should load from the res/raw or the Assets folder.

After that, the method creates a InputStream object (line 63). Streams are like handles to read files into buffers (Input Stream) and to write files from these buffers (Output stream).

Line 65 checks if the loadFromRawFolder parameter is true. Case it is, the code at lines 68 and 70 is executed. The former dynamically loads resources from the raw folder. The getIdentifier() method from the resources object returns a resource ID based on the path. This parameter is composed by:

package name:type of resource/file name

Package name is self explanatory; type of resource can be one of the following: raw, drawable, string. File name, in this example, is the fileName parameter, an it’s being concatenated to create one single String. Since all information that this method requires is being passed on the first parameter the other two can be null.

Finally, line 70 feeds this ID to the openRawResource() method, which will return a InputStream from a file located at the res/raw folder.

At the else block, the Assets folder is being opened, by first calling the getAssets() method to return a handle to the Assets folder and right after that, the open() method is called, passing the fileName as the parameter. All that is done to also return the InputStream, although this time, for a file at the Assets folder (line 75).

Now that we have the InputStream, we can create the buffer to read the file into. That’s accomplished by line 79, that creates a byte array that has exactly the same length as iS (the InputStream object). The file is read into the buffer at the next line (line 81).

With the file loaded into the buffer, it’s time to prepare a OutputStream to write the buffer contents into. First, a object of this type is created at line 83. Then, the write() method is called passing the buffer as the parameter (line 85). With that, a handle to the file’s content was created.

There’s nothing left to do with these two streams, so they are closed at lines 87 and 88. Finally, the return for this method is set, by converting the oS object to a String (line 91).

At last, the LoadFile() method is called at line 33 (don’t forget to omit the file extension) and at line 47 (don’t forget to include the file extension). Both method calls are surrounded by a try/catch block since they can throw an exception.

The returned String from the method calls are stored at the output variable. It’s then later used to print the contents of the loaded files into LogCat’s console (lines 35 and 49).

And that’s about it! The method that was declared in the Activity can be easily adapted to load and return anything from these folders, not just a String. Additionally, it can be used to dynamically to acquire a reference, and load files at run time.

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Loading html file to webview on android from assets folder using Android Studio

I’m using Android Studio/Gradle.

app\src\main\android_asset folder has the file called chart.html..

I’m trying to load this file to my webview like this:

But I always get the error: could not be loaded because ERR_FILE_NOT_FOUND.

What am I missing here?

3 Answers 3

The directory name should be assets not android_assets

Do like this:

As shown in the above pics just right click on your app->New->Folder->Assets Folder

Now put your .html file here in assets folder.

Remaining is same in code what you did.

I use many productFlavors with different applicationId.

If I attempt to load a html file from res/raw/file.html I get a ClassNotFoundException Didn’t find class «product.flavor.package.R$raw»

The R.java file has a different Package name.

It look’s like you can’t load a URL from file like : webView.loadUrl( «file:///android_res/raw/page.html»); because the WebView try to use the R.class file with has a different package name.

I assume the ERR_FILE_NOT_FOUND from loading a html file from assets has the same problem but you don’t see the exception. ( webView.loadUrl( «file:///android_assets/page.html» ); )

With this small work around I solve my problem :

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Load a file from assets folder in android studio

I was wondering if there is a way to access a file and it’s path from my assets folder in android studio? The reason why I need to access the file and its path is because I am working with a method that REQUIRES the String path for a file, and it must access the file from its String path. However, in android studio I haven’t found a way to access the file directly from the String value of its path. I decided to use a workaround and simply read the file from an InputStream and write the file to an OutputStream, but the file is about 170MB, and it is too memory intensive to write the File to an OutputStream. It takes my application about 10:00 Minutes to download the file when I implement that strategy. I have searched all over this website and numerous sources to find a solution (books and documentation) but am unable to find a viable solution. Here is an example of my code:

As you can see the TDBLoader.loadModel() method requires a String for the file URI as the second argument, so it would be convenient to have the ability to access the File directly from my assets folder without utilizing an InputStream. The method takes as an argument (Model model, String url, Boolean showProgress). As I mentioned, the current strategy I am using utilizes too much memory and either crashes the Application entirely, or takes 10 minutes to download the file I need. I am using an AsyncTask to perform this operation, but due to the length of time required to perform the task that kind of defeats the purpose of an AsyncTask in this scenario.

What further complicates things is that I have to use an old version of Apache Jena because I am working with Android Studio and the official version of Apache Jena is not compatible with android studio. So I have to use a port that is 8 years old which doesn’t have the updated classes that Apache Jena offers. If I could use the RDFParser class I could pass an InputStream, but that class does not exist in the older version of Apache Jena that I must use.

So I am stuck at this point. The method must utilize the String url path of the file in my assets folder, but I don’t know how to access this without writing to a custom file from an InputStream, but writing to the file from the InputStream utilizes too much memory and forces the App to crash. If anyone has a solution I will greatly appreciate it.

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Load files bigger than 1M from assets folder

I’m going crazy, I created a file object, so it can be read with ObjectInputStream, and I placed the assets folder. The method works with a file smaller than 1M, and give error with larger files. I read that is a limit of Android platform, but I also know that can be «easily» avoided. Those who have downloaded the game Reging Thunder, for example, can easily see that in their assets folder is a file 18.9M large. This is my code for read 1 object from a ObjecInputStream

now I have an uncompressed file and I can use it without worrying about the error «This file can not be opened as a file descriptor; it is probably compressed»

This function works well with files smaller than 1M, with bigger files return an java.io.IOException on line «ObjectInputStream ois=new ObjectInputStream(is);»

11 Answers 11

Faced the same issue. I’ve cut up my 4MB file into 1 MB chunks, and on the first run I join the chunks into a data folder on the phone. As an added bonus, the APK is properly compressed. The chunk files are called 1.db, 2.db, etc. The code goes like this:

The limitation is on compressed assets. If the asset is uncompressed, the system can memory-map the file data and use the Linux virtual memory paging system to pull in or discard 4K chunks as appropriate. (The «zipalign» tool ensures that uncompressed assets are word-aligned in the file, which means they’ll also be aligned in memory when directly mapped.)

If the asset is compressed, the system has to uncompress the entire thing to memory. If you have a 20MB asset, that means 20MB of physical memory is tied up by your application.

Ideally the system would employ some sort of windowed compression, so that only parts need to be present, but that requires some fanciness in the asset API and a compression scheme that works well with random access. Right now APK == Zip with «deflate» compression, so that’s not practical.

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