Android Internal Storage Example Tutorial

来源:互联网 时间:1970-01-01

Android offers a few structured ways to store data . These include

Shared Preferences Internal Storage External Storage SQLite Storage Storage via Network Connection(on cloud)

In this tutorial we are going to look into the saving and reading data into files using Android Internal Storage .

Android Internal Storage

Android Internal storage is the storage of the private data on the device memory. By default, saving and loading files to the internal storage are private to the application and other applications will not have access to these files. When the user uninstalls the applications the internal stored files associated with the application are also removed. However, note that some users root their Android phones, gaining superuser access. These users will be able to read and write whatever files they wish.

Reading and Writing Text File in Android Internal Storage

Android offers openFileInput and openFileOutput from the Java I/O classes to modify reading and writing streams from and to local files.

openFileOutput() : This method is used to create and save a file. It’s syntax is given below: FileOutputStream fOut = openFileOutput("file name",Context.MODE_PRIVATE);

The method openFileOutput() returns an instance of FileOutputStream . After that we can call write method to write data on the file. Its syntax is given below:

String str = "test data";fOut.write(str.getBytes());fOut.close(); openFileInput()

: This method is used to open a file and read it. It returns an instance of FileInputStream. Its syntax is given below:

FileInputStream fin = openFileInput(file);

After that, we call read method to read one character at a time from the file and then print it. Its syntax is given below:

int c;String temp="";while( (c = fin.read()) != -1){ temp = temp + Character.toString((char)c);}fin.close();

In the above code, string temp contains all the data of the file.

Note that these methods do not accept file paths (e.g. path/to/file.txt), they just take simple file names. Project Structure

Code

The xml layout contains an EditText to write data to the file and a Write Button and Read Button. Note that the onClick methods are defined in the xml file only as shown below:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"><TextViewandroid:id="@+id/textView1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentLeft="true"android:layout_alignParentRight="true"android:padding="5dp"android:text="Android Read and Write Text from/to a File"android:textStyle="bold"android:textSize="28sp" /><EditTextandroid:id="@+id/editText1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentLeft="true"android:layout_alignParentRight="true"android:layout_below="@+id/textView1"android:layout_marginTop="22dp"android:minLines="5"android:layout_margin="5dp"><requestFocus /></EditText><Buttonandroid:id="@+id/button1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Write Text into File"android:onClick="WriteBtn"android:layout_alignTop="@+id/button2"android:layout_alignRight="@+id/editText1"android:layout_alignEnd="@+id/editText1" /><Buttonandroid:id="@+id/button2"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Read Text From file"android:onClick="ReadBtn"android:layout_centerVertical="true"android:layout_alignLeft="@+id/editText1"android:layout_alignStart="@+id/editText1" /></RelativeLayout>

The MainActivity contains the implementation of the reading and writing to files as it was explained above.

package com.journaldev.internalstorage;import android.os.Bundle;import android.app.Activity;import android.view.View;import android.widget.EditText;import android.widget.Toast;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.InputStreamReader;import java.io.OutputStreamWriter;public class MainActivity extends Activity {EditText textmsg;static final int READ_BLOCK_SIZE = 100;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);textmsg=(EditText)findViewById(R.id.editText1);}// write text to filepublic void WriteBtn(View v) {// add-write text into filetry {FileOutputStream fileout=openFileOutput("mytextfile.txt", MODE_PRIVATE);OutputStreamWriter outputWriter=new OutputStreamWriter(fileout);outputWriter.write(textmsg.getText().toString());outputWriter.close();//display file saved messageToast.makeText(getBaseContext(), "File saved successfully!",Toast.LENGTH_SHORT).show();} catch (Exception e) {e.printStackTrace();}}// Read text from filepublic void ReadBtn(View v) {//reading text from filetry {FileInputStream fileIn=openFileInput("mytextfile.txt");InputStreamReader InputRead= new InputStreamReader(fileIn);char[] inputBuffer= new char[READ_BLOCK_SIZE];String s="";int charRead;while ((charRead=InputRead.read(inputBuffer))>0) {// char to string conversionString readstring=String.copyValueOf(inputBuffer,0,charRead);s +=readstring;}InputRead.close();textmsg.setText(s);} catch (Exception e) {e.printStackTrace();}}}

Here, a toast is displayed when data is successfully written into the internal storage and the data is displayed in the EditText itself on reading the data from the file.

The image shown below is the output of the project. The image depicts text being written to the internal storage and on clicking Read it displays back the text in the same EditText.

Where is the file located?

To actually view the file open the Android Device Monitor from Tools->Android->Android Device Monitor.

The file is present in the folder data->data->{package name}->files as shown in the images below:

The file “mytextfile.txt” is found in the package name of the project i.e. com.journaldev.internalstorage as shown below:

Download the final project for android internal storage example from below link.

Download Android Internal Storage Example Project 1 downloads


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