In this tutorial you will learn via examples how to create or delete files in the android ecosystem.
Example 1: Create, Read and Delete a File in External Storage
This example project will teach you the following concepts:
- How to create a file in the android external storage.
- How to read a file in the android external storage.
- How to delete a file from the sd card.
- How to implement runtime permissions in Java android.
- How to create a file in the background thread using AsyncTask.
Here is the demo screenshot:
Step 1: Create Project
The first step is to create a Android Project in Android Studio.
Step 2: Add Dependencies
No special or third party dependencies are needed for this project.
Step 3: Design Layouts
Design your layout as follows:
activity_main.xml
Add a TextView, button and edittext:
<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout
tools:context="com.example.ankitkumar.asynctask.MainActivity"
android:background="#F58F"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:id="@+id/activity_main"
xmlns:tools="http://schemas.android.com/tools"
xmlns:android="http://schemas.android.com/apk/res/android">
<LinearLayout
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:id="@+id/ll_for_enter_data"
android:weightSum="3"
android:orientation="horizontal">
<EditText
android:background="#ffffF1"
android:layout_height="75dp"
android:layout_width="0dp"
android:id="@+id/ed_enter_data"
android:layout_weight="2.25"/>
<Button
android:layout_height="75dp"
android:layout_width="0dp"
android:id="@+id/button_add"
android:layout_weight="0.75"
android:text="Add Data"/>
</LinearLayout>
<TextView
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:id="@+id/tv_title"
android:text="Content from file"
android:textColor="#eae8c2"
android:layout_centerHorizontal="true"
android:layout_marginTop="10dp"
android:layout_below="@+id/ll_for_enter_data"
android:textSize="18sp"/>
<TextView
android:background="#303F9F"
android:layout_height="100dp"
android:layout_width="match_parent"
android:id="@+id/tv_show_data"
android:text="Data from file"
android:textColor="#000000"
android:layout_marginTop="10dp"
android:layout_below="@+id/tv_title"
android:textSize="16sp"/>
<Button
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:id="@+id/button_delete"
android:text="Delete File"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"/>
</RelativeLayout>Step : Write Code
Go to your MainActivity.java and add imports including the following:
import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;Extend the AppCompatActivity and implement the View.OnClickListener:
public class MainActivity extends AppCompatActivity implements View.OnClickListener{Define the following constants:
static final Integer LOCATION = 0x1;
static final Integer CALL = 0x2;
static final Integer WRITE_EXST = 0x3;
static final Integer READ_EXST = 0x4;
static final Integer CAMERA = 0x5;
static final Integer ACCOUNTS = 0x6;
static final Integer GPS_SETTINGS = 0x7;
String myData = "";Instantiate a File and pass the path of the file creation as below:
final File myFile = new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/TestFile.txt");Define our views:
Button buttonAdd, buttonDelete;
EditText editTextForSave;
TextView textViewForShowData;Override our onCreate():
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editTextForSave = (EditText) findViewById(R.id.ed_enter_data);
textViewForShowData = (TextView) findViewById(R.id.tv_show_data);
buttonAdd = (Button) findViewById(R.id.button_add);
buttonDelete = (Button) findViewById(R.id.button_delete);
buttonAdd.setOnClickListener(this);
buttonDelete.setOnClickListener(this);
}Here is how we create a method that will ask for permission at runtime:
private void askForPermission(String permission, Integer requestCode) {
if (ContextCompat.checkSelfPermission(MainActivity.this, permission) != PackageManager.PERMISSION_GRANTED) {
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, permission)) {
//This is called if user has denied the permission before
//In this case I am just asking the permission again
ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);
} else {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);
}
} else {
//Toast.makeText(this, "" + permission + " is already granted.", Toast.LENGTH_SHORT).show();
}
}Here is how invoke that method:
public void ask(View v){
switch (v.getId()){
case R.id.button_add:
askForPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE,WRITE_EXST);
new MyAsynTask().execute();
break;
case R.id.button_delete:
askForPermission(Manifest.permission.READ_EXTERNAL_STORAGE,READ_EXST);
deleteFile();
break;
default:
break;
}
}And here is how we handle the permission result using the onRequestPermissionsResult():
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if(ActivityCompat.checkSelfPermission(this, permissions[0]) == PackageManager.PERMISSION_GRANTED){
switch (requestCode) {
case 3:
writeFile();
break;
//Read External Storage
case 4:
Intent imageIntent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(imageIntent, 11);
break;
}
Toast.makeText(this, "Permission granted", Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this, "Permission denied", Toast.LENGTH_SHORT).show();
}
}Here is how we write to a file on the SD card using the OutputStreamWriter:
public void writeFile(){
// write on SD card file data in the text box
try {
// buttonAdd.setEnabled(false);
FileOutputStream fOut = new FileOutputStream(myFile);
final OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
String temp=editTextForSave.getText().toString();
myOutWriter.append(temp);
myOutWriter.append("\n");
myOutWriter.close();
fOut.close();
Log.e("MA : ","Done writing SD");
} catch (Exception e) {
Log.e("catch : ",e.getMessage());
}
// editTextForSave.setText("");
// buttonAdd.setEnabled(true);
}Here is how we read a file in the external storage using the BufferedReader:
public void showData(){
try {
FileInputStream fis = new FileInputStream(myFile);
DataInputStream in = new DataInputStream(fis);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
while ((strLine = br.readLine()) != null) {
myData = myData + "\n" + strLine;
}
in.close();
} catch (IOException e) {
e.printStackTrace();
}
// textViewForShowData.setText(myData);
}Here is we delete a file from the SD card programmatically in android:
public void deleteFile(){
myFile.delete();
myData = "";
textViewForShowData.setText("File no Longer Exist.");
Log.e("MA : ","File Deleted");
}Here is how we implement the asyncTask to write and read our data in the external storage:
// The definition of our task class
private class MyAsynTask extends AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... params) {
writeFile();
showData();
return "All Done!";
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
buttonAdd.setEnabled(false);
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
textViewForShowData.setText(myData);
editTextForSave.setText("");
buttonAdd.setEnabled(true);
}
}
}Here is the full code for the MainActivity:
MainActivity.java
package com.example.ankitkumar.asynctask;
import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
static final Integer LOCATION = 0x1;
static final Integer CALL = 0x2;
static final Integer WRITE_EXST = 0x3;
static final Integer READ_EXST = 0x4;
static final Integer CAMERA = 0x5;
static final Integer ACCOUNTS = 0x6;
static final Integer GPS_SETTINGS = 0x7;
String myData = "";
final File myFile = new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/TestFile.txt");
Button buttonAdd, buttonDelete;
EditText editTextForSave;
TextView textViewForShowData;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editTextForSave = (EditText) findViewById(R.id.ed_enter_data);
textViewForShowData = (TextView) findViewById(R.id.tv_show_data);
buttonAdd = (Button) findViewById(R.id.button_add);
buttonDelete = (Button) findViewById(R.id.button_delete);
buttonAdd.setOnClickListener(this);
buttonDelete.setOnClickListener(this);
}
private void askForPermission(String permission, Integer requestCode) {
if (ContextCompat.checkSelfPermission(MainActivity.this, permission) != PackageManager.PERMISSION_GRANTED) {
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, permission)) {
//This is called if user has denied the permission before
//In this case I am just asking the permission again
ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);
} else {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);
}
} else {
//Toast.makeText(this, "" + permission + " is already granted.", Toast.LENGTH_SHORT).show();
}
}
public void ask(View v){
switch (v.getId()){
case R.id.button_add:
askForPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE,WRITE_EXST);
new MyAsynTask().execute();
break;
case R.id.button_delete:
askForPermission(Manifest.permission.READ_EXTERNAL_STORAGE,READ_EXST);
deleteFile();
break;
default:
break;
}
}
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if(ActivityCompat.checkSelfPermission(this, permissions[0]) == PackageManager.PERMISSION_GRANTED){
switch (requestCode) {
case 3:
writeFile();
break;
//Read External Storage
case 4:
Intent imageIntent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(imageIntent, 11);
break;
}
Toast.makeText(this, "Permission granted", Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this, "Permission denied", Toast.LENGTH_SHORT).show();
}
}
@Override
public void onClick(View v) {
ask(v);
}
public void writeFile(){
// write on SD card file data in the text box
try {
// buttonAdd.setEnabled(false);
FileOutputStream fOut = new FileOutputStream(myFile);
final OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
String temp=editTextForSave.getText().toString();
myOutWriter.append(temp);
myOutWriter.append("\n");
myOutWriter.close();
fOut.close();
Log.e("MA : ","Done writing SD");
} catch (Exception e) {
Log.e("catch : ",e.getMessage());
}
// editTextForSave.setText("");
// buttonAdd.setEnabled(true);
}
public void showData(){
try {
FileInputStream fis = new FileInputStream(myFile);
DataInputStream in = new DataInputStream(fis);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
while ((strLine = br.readLine()) != null) {
myData = myData + "\n" + strLine;
}
in.close();
} catch (IOException e) {
e.printStackTrace();
}
// textViewForShowData.setText(myData);
}
public void deleteFile(){
myFile.delete();
myData = "";
textViewForShowData.setText("File no Longer Exist.");
Log.e("MA : ","File Deleted");
}
// The definition of our task class
private class MyAsynTask extends AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... params) {
writeFile();
showData();
return "All Done!";
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
buttonAdd.setEnabled(false);
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
textViewForShowData.setText(myData);
editTextForSave.setText("");
buttonAdd.setEnabled(true);
}
}
}Run
Copy the code into your project or download the code in the reference links below.
Reference
Find the reference links below:
| Number | Link |
|---|---|
| 1. | Download code |
| 2. | Follow code author |
