Essential Books

Fetch Device Directory

suggest change

First Add Storage permission to read/fetch device directory. 

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Create model class 

//create one directory model class
//to store directory title and type in list

public class DirectoryModel {
    String dirName;
    int dirType; // set 1 or 0, where 0 for directory and 1 for file.

    public int getDirType() {
        return dirType;
    }

    public void setDirType(int dirType) {
        this.dirType = dirType;
    }

    public String getDirName() {
        return dirName;
    }

    public void setDirName(String dirName) {
        this.dirName = dirName;
    }
}

Create list using directory model to add directory data. 

//define list to show directory

List<DirectoryModel> rootDir = new ArrayList<>();

Fetch directory using following method. 

//to fetch device directory

private void getDirectory(String currDir) { // pass device root directory
        File f = new File(currDir);
        File[] files = f.listFiles();
        if (files != null) {
            if (files.length > 0) {
                rootDir.clear();
                for (File inFile : files) {
                    if (inFile.isDirectory()) { //return true if it's directory
                        // is directory
                        DirectoryModel dir = new DirectoryModel();
                        dir.setDirName(inFile.toString().replace("/storage/emulated/0", ""));
                        dir.setDirType(0); // set 0 for directory
                        rootDir.add(dir);
                    } else if (inFile.isFile()) { // return true if it's file
                        //is file
                        DirectoryModel dir = new DirectoryModel();
                        dir.setDirName(inFile.toString().replace("/storage/emulated/0", ""));
                        dir.setDirType(1); // set 1 for file
                        rootDir.add(dir);
                    }
                }
            }
            printDirectoryList();
        }
    }

Print directory list in log. 

//print directory list in logs

private void printDirectoryList() {
    for (int i = 0; i < rootDir.size(); i++) {
        Log.e(TAG, "printDirectoryLogs: " + rootDir.get(i).toString());
    }
}

Usage 

//to Fetch Directory Call function with root directory.

String rootPath = Environment.getExternalStorageDirectory().toString(); // return ==>  /storage/emulated/0/
getDirectory(rootPath );

To fetch inner files/folder of specific directory use same method just change argument, pass the current selected path in argument and handle response for same.

To get File Extension : 

private String getExtension(String filename) {

    String filenameArray[] = filename.split("\\.");
    String extension = filenameArray[filenameArray.length - 1];
    Log.d(TAG, "getExtension: " + extension);

    return extension;
}
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Storing Files in Internal and External Storage:
* Storing Files in Internal External Storage
* Android Internal and External Storage - Terminology Clarification
* Using External Storage
* Using Internal Storage
* Save Database on SD Card Backup DB on SD
* Fetch Device Directory
Table Of Contents
0 Getting Started
1 Layouts
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4 NavigationView
5 Intent
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258 Annotation Processor
259 SyncAdapter with periodically do sync of data
260 Singleton Class for Toast Message
261 Fastjson
262 Android Architecture Components
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265 Loading Bitmaps Effectively
266 Getting system font names
267 Smartcard
268 Convert vietnamese string to english
269 Contributors