1. Android – Read/Write to External Storage
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage 1

2. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
Android External Storage: a place to store addition data  of Android, the files that you store here is not applied the security system.
Usually there are two types of external storage: 
Fixed external storage: Commonly understood as the hard drive of the device.
Removable  storage: Such as SD Card. 
Use the static method of Environment class  you can get the information on the directory of the external storage.
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

3. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
Android External Storage
The table below results running on the emulator device.
To read/write the data on the external storage requires you to configureAndroidManifest.xml, added:
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

4. Read and write files on the external storage example
AndroidManifest.xml configuration allows read and write data on the external storage memory.
Full content of 
AndroidManifest.xml:
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

5. Read and write files on the external storage example
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="
    xmlns:tools="
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
 <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true">
        <requestFocus />
    </EditText>
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="120dp"
        android:layout_marginTop="10dp" />
   <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="save"
        android:layout_alignParentBottom="true"
/>
    <Button
        android:text="read" />
        style="?android:attr/buttonStyleSmall"
        android:text="List Dirs"
/>
</RelativeLayout>
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

6. Read and write files on the external storage example
public class MainActivity extends Activity {
   private EditText editText;
   private TextView textView;
   private Button saveButton;
   private Button readButton;
   private Button listButton;   
   private static final int REQUEST_ID_READ_PERMISSION = 100;
   private static final int REQUEST_ID_WRITE_PERMISSION = 200;
   private final String fileName = "note.txt";
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);
       editText = (EditText) findViewById(R.id.editText);
       textView = (TextView) findViewById(R.id.textView);
       saveButton = (Button) findViewById(R.id.button_save);
       readButton = (Button) findViewById(R.id.button_read);
       listButton = (Button) findViewById(R.id.button_list);
       saveButton.setOnClickListener(new OnClickListener() {
           public void onClick(View arg0) {
               askPermissionAndWriteFile();
           }
       });
MainActivity.java
import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.ActivityCompat;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

7. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
MainActivity.java  Contd
readButton.setOnClickListener(new OnClickListener() {
           public void onClick(View arg0) {
               askPermissionAndReadFile();
           }
       });
       listButton.setOnClickListener(new OnClickListener() {
               listExternalStorages();
   }
   private void askPermissionAndWriteFile() {
       boolean canWrite = this.askPermission(REQUEST_ID_WRITE_PERMISSION,
               Manifest.permission.WRITE_EXTERNAL_STORAGE);
       //
       if (canWrite) {
           this.writeFile();
       }
   }
   private void askPermissionAndReadFile() {
       boolean canRead = this.askPermission(REQUEST_ID_READ_PERMISSION,
               Manifest.permission.READ_EXTERNAL_STORAGE);
       if (canRead) {
           this.readFile();
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

8. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
   // When you have the request results
MainActivity.java  Contd
   public void onRequestPermissionsResult(int requestCode,
                                          String permissions[], int[] grantResults) {
       super.onRequestPermissionsResult(requestCode, permissions, grantResults);
       //
       // Note: If request is cancelled, the result arrays are empty.
       if (grantResults.length > 0) {
           switch (requestCode) {
               case REQUEST_ID_READ_PERMISSION: {
                   if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                       readFile();
                   }
               }
               case REQUEST_ID_WRITE_PERMISSION: {
                       writeFile();
           }
       } else {
           Toast.makeText(getApplicationContext(), "Permission Cancelled!", Toast.LENGTH_SHORT).show();
       }
   }
 // With Android Level >= 23, you have to ask the user
   // for permission with device (For example read/write data on the device).
private boolean askPermission(int requestId, String permissionName) {
       if (android.os.Build.VERSION.SDK_INT >= 23) {
           // Check if we have permission
           int permission = ActivityCompat.checkSelfPermission(this, permissionName);
           if (permission != PackageManager.PERMISSION_GRANTED) {
               // If don't have permission so prompt the user.
               this.requestPermissions(
                       new String[]{permissionName},
                       requestId
               );
               return false;
           }
       }
       return true;
   }
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

9. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
MainActivity.java  Contd
private void writeFile() {
   
       File extStore = Environment.getExternalStorageDirectory();
       // ==> /storage/emulated/0/note.txt
       String path = extStore.getAbsolutePath() + "/" + fileName;
       Log.i("ExternalStorageDemo", "Save to: " + path);
       String data = editText.getText().toString();
       try {
           File myFile = new File(path);
           myFile.createNewFile();
           FileOutputStream fOut = new FileOutputStream(myFile);
           OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
           myOutWriter.append(data);
           myOutWriter.close();
           fOut.close();
           Toast.makeText(getApplicationContext(), fileName + " saved", Toast.LENGTH_LONG).show();
       } catch (Exception e) {
           e.printStackTrace();
       }
   }
 private void readFile() {
   
       File extStore = Environment.getExternalStorageDirectory();
       // ==> /storage/emulated/0/note.txt
       String path = extStore.getAbsolutePath() + "/" + fileName;
       Log.i("ExternalStorageDemo", "Read file: " + path);
       String s = "";
       String fileContent = "";
       try {
           File myFile = new File(path);
           FileInputStream fIn = new FileInputStream(myFile);
           BufferedReader myReader = new BufferedReader(
                   new InputStreamReader(fIn));
           while ((s = myReader.readLine()) != null) {
               fileContent += s + "\n";
           }
           myReader.close();
           this.textView.setText(fileContent);
       } catch (IOException e) {
           e.printStackTrace();
       }
       Toast.makeText(getApplicationContext(), fileContent, Toast.LENGTH_LONG).show();
   }
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

10. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
   private void listExternalStorages() {
       StringBuilder sb = new StringBuilder();
        sb.append("Data Directory: ").append("\n - ")
               .append(Environment.getDataDirectory().toString()).append("\n");
        sb.append("Download Cache Directory: ").append("\n - ")
               .append(Environment.getDownloadCacheDirectory().toString()).append("\n");
        sb.append("External Storage State: ").append("\n - ")
               .append(Environment.getExternalStorageState().toString()).append("\n");
        sb.append("External Storage Directory: ").append("\n - ")
               .append(Environment.getExternalStorageDirectory().toString()).append("\n");
        sb.append("Is External Storage Emulated?: ").append("\n - ")
               .append(Environment.isExternalStorageEmulated()).append("\n");
        sb.append("Is External Storage Removable?: ").append("\n - ")
               .append(Environment.isExternalStorageRemovable()).append("\n");
        sb.append("External Storage Public Directory (Music): ").append("\n - ")
               .append(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC).toString()).append("\n");
       sb.append("Download Cache Directory: ").append("\n - ")
       sb.append("Root Directory: ").append("\n - ")
               .append(Environment.getRootDirectory().toString()).append("\n");
       Log.i("ExternalStorageDemo", sb.toString());
       this.textView.setText(sb.toString());
   } }
MainActivity.java  Contd
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

11. Read and write files on the external storage example
Output
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage

12. S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage
Thank You
12 September 2018
S.RENUKADEVI/AP/SCD/ANDROID - Read/Write to External Storage