Preferences and the database, but sometimes, just a simple file and also to meet the demand for data storage. Android offering two ways to access files: one for the file type is packed with your application and a file type to be created by your application on the device.
In this chapter, I presented a sample project to accessing 2 these type of files which an application usually interacts with them, hope that you can understand more about storing and retrieving files in Android. Source code now available on @Github.
DEMO VIDEO:
Assets Files - packed with your application
main/assets/ folder. You can use it to store raw asset files. Files that you save here are compiled into an .apk file as-is, and the original file name is preserved. You can navigate this directory in the same way as a typical file system using URIs and read files as a stream of bytes using the AssetManager. For example, this is a good location for textures and game data.In general, assuming you have some static data want to include with the application, such as a list of words for a spelling checker. The easiest way to do this is to place the file in the
res/assets folder, from which it will be placed inside the Android APK file of applications in the packaging process as a raw resource. Maybe I have a text file in it:
Resources type. In order to access it, you need an AssetManager instance, usually initialized by call getAssets() in your current Context (usually is an Activity). After that, like accessing file in Java platform, defining a BufferedReader object with InputStreamReader to read this text file line by line and show this content to a TextView after completed:
public void readAssetsFile() {
String fileString = "";
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(getAssets().open("lorem_ipsum.txt"), "UTF-8"));
// do reading, usually loop until end of file reading
String line;
while ((line = reader.readLine()) != null) {
//process line
fileString += line;
}
//set result to TextView after finish reading
textView.setText(fileString);
} catch (IOException e) {
e.printStackTrace();
textView.setError("Cannot open file!");
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
Button:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
button1 = findViewById(R.id.btn_1);
button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
readAssetsFile(); //read a file in res/assets folder
}
});
}
As note above, res/assets folder used for saving raw resource files. For another cases, you can save the database file (.db) or other file types which providing data to your application, readers find out yourself the way to access and use them!
Files in external memory - Huge storage space
To access a file located in a folder of SD card, you must find the directory for the SD Card by using
getExternalStorageDirectory() and specify the correct file name:
//Find the directory for the SD Card using the API
//*Don't* hardcode "/sdcard"
File sdcard = Environment.getExternalStorageDirectory();
//Get the text file based on folder
File file = new File(sdcard, "Test/introduce.txt");
BufferedReader initialized with a FileReader instance:
public void readFromSDcard() {
//Find the directory for the SD Card using the API
//*Don't* hardcode "/sdcard"
File sdcard = Environment.getExternalStorageDirectory();
//Get the text file based on folder
File file = new File(sdcard, "Test/introduce.txt");
//Read text from file
StringBuilder text = new StringBuilder();
try {
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
text.append(line);
text.append('\n');
}
br.close();
} catch (IOException e) {
//You'll need to add proper error handling here
}
//Set the text
textView.setText(text);
}
onCreate():
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
button2 = findViewById(R.id.btn_2);
button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
readFromSDcard();
}
});
}
TextView:
AndroidManifest.xml to use this feature:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
FileOutputStream and attach with it an OutputStreamWriter instance. Never forget call File.createNewFile() before writing data:
public void writeTextToFile() {
if (editText.getText().toString().trim().equals("")) {
Toast.makeText(this, "Please input some texts", Toast.LENGTH_SHORT).show();
} else {
try {
File sdcard = Environment.getExternalStorageDirectory();
//Get the text file based on folder
File file = new File(sdcard, "Test/output.txt");
file.createNewFile();
FileOutputStream fOut = new FileOutputStream(file);
OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
//get EditText content to OutputStreamWriter
myOutWriter.append(editText.getText().toString().trim());
myOutWriter.close();
fOut.close();
Toast.makeText(this, "Done writing File to SD card!", Toast.LENGTH_SHORT).show();
} catch (Exception e) {
e.printStackTrace();
}
}
}
Toast will show:
NOTE: Remember providing write data to SD card permission in
AndroidManifest.xml to use this feature:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
Other file type?
Bitmap with BitmapFactory, you can easily to get it to an ImageView:
ImageActivity.java
This is output screen:package info.devexchanges.accessingfiles;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ImageView;
import java.io.File;
public class ImageActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_image);
View button = findViewById(R.id.btn_get);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
File sdcard = Environment.getExternalStorageDirectory();
//Get PNG file based on folder
File imgFile = new File(sdcard, "Test/logo.png");
if(imgFile.exists()){
//decode Bitmap by BitmapFactory
Bitmap bitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());
//set Bitmap to ImageView
ImageView imageView = (ImageView) findViewById(R.id.image);
imageView.setImageBitmap(bitmap);
}
}
});
}
}
Conclusions
