একটি পেশাদার অ্যান্ড্রয়েড অ্যাপ তৈরি করার সর্বোত্তম উপায়। সোর্স কোড – 1. WebView Android App Code:
MainActivity.java

import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

String websiteURL = "https://kamrulbd.com/"; // sets web url
private WebView webview;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Webview stuff
    webview = findViewById(R.id.webView);
    webview.getSettings().setJavaScriptEnabled(true);
    webview.getSettings().setDomStorageEnabled(true);
    webview.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
    webview.loadUrl(websiteURL);
    webview.setWebViewClient(new WebViewClientDemo());

}

private class WebViewClientDemo extends WebViewClient {
    @Override
    //Keep webview in app when clicking links
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }
}

}
AndroidManifest.xml

2. Internet Connection Error:
   AndroidManifest.xml

MainActivity.java

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.util.Log;
import android.webkit.WebView;
import android.webkit.WebViewClient;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

String websiteURL = "https://viskill.in/"; // sets web url
private WebView webview;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if( ! CheckNetwork.isInternetAvailable(this)) //returns true if internet available
    {
        //if there is no internet do this
        setContentView(R.layout.activity_main);
        //Toast.makeText(this,"No Internet Connection, Chris",Toast.LENGTH_LONG).show();

        new AlertDialog.Builder(this) //alert the person knowing they are about to close
                .setTitle("No internet connection available")
                .setMessage("Please Check you're Mobile data or Wifi network.")
                .setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        finish();
                    }
                })
                //.setNegativeButton("No", null)
                .show();

    }
    else
    {
        //Webview stuff
        webview = findViewById(R.id.webView);
        webview.getSettings().setJavaScriptEnabled(true);
        webview.getSettings().setDomStorageEnabled(true);
        webview.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
        webview.loadUrl(websiteURL);
        webview.setWebViewClient(new WebViewClientDemo());

    }
}


private class WebViewClientDemo extends WebViewClient {
    @Override
    //Keep webview in app when clicking links
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }
}

}

class CheckNetwork {

private static final String TAG = CheckNetwork.class.getSimpleName();

public static boolean isInternetAvailable(Context context)
{
    NetworkInfo info = (NetworkInfo) ((ConnectivityManager)
            context.getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo();

    if (info == null)
    {
        Log.d(TAG,"no internet connection");
        return false;
    }
    else
    {
        if(info.isConnected())
        {
            Log.d(TAG," internet connection available...");
            return true;
        }
        else
        {
            Log.d(TAG," internet connection");
            return true;
        }

    }
}

}

3. Back & Exit Feature:
   MainActivity.java

//set back button functionality
@Override
public void onBackPressed() { //if user presses the back button do this
if (webview.isFocused() && webview.canGoBack()) { //check if in webview and the user can go back
webview.goBack(); //go back in webview
} else { //do this if the webview cannot go back any further

    new AlertDialog.Builder(this) //alert the person knowing they are about to close
            .setTitle("EXIT")
            .setMessage("Are you sure. You want to close this app?")
            .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    finish();
                }
            })
            .setNegativeButton("No", null)
            .show();
}

}

4. Swipe Down to Refresh:
   activity_main.xml

<WebView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/webView"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentBottom="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true"
    tools:ignore="MissingConstraints" />

MainActivity.java

SwipeRefreshLayout mySwipeRefreshLayout;
//Swipe to refresh functionality
mySwipeRefreshLayout = (SwipeRefreshLayout)this.findViewById(R.id.swipeContainer);

mySwipeRefreshLayout.setOnRefreshListener(
new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
webview.reload();
}
}
);
private class WebViewClientDemo extends WebViewClient {
@Override
//Keep webview in app when clicking links
public boolean shouldOverrideUrlLoading(WebView view, String url) {
view.loadUrl(url);
return true;
}
@Override
public void onPageFinished(WebView view, String url) {
super.onPageFinished(view, url);
mySwipeRefreshLayout.setRefreshing(false);
}
}

5. Screen Rotation:
   AndroidManifest.xml

android:screenOrientation=”portrait”>

6. Splash Screen:
   SplashActivity.java import androidx.appcompat.app.AppCompatActivity; import android.content.Intent; import android.os.Bundle; import android.view.Window; import android.view.WindowManager; public class SplashActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState); Window window = getWindow() ; window.addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN); setContentView(R.layout.activity_splash); Thread splashTread = new Thread(){ @Override public void run() { try { sleep(3000); startActivity(new Intent(getApplicationContext(),MainActivity.class)); finish(); } catch (InterruptedException e) { e.printStackTrace(); } super.run(); } }; splashTread.start();} }
   activity_splash

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    tools:context=".SplashActivity">


    <ImageView

        android:layout_width="match_parent"

        android:layout_height="300dp"

        android:src="@drawable/logo"

        android:scaleType="centerCrop"

        android:padding="50dp"

        android:layout_marginTop="220dp"/>

    <ProgressBar

        android:layout_width="220dp"

        android:layout_height="10dp"

        android:layout_gravity="center_horizontal"

        style="?android:attr/progressBarStyleHorizontal"

        android:max="100"

        android:indeterminate="true"

        android:progress="0"

        android:layout_marginTop="100dp"


        />



</LinearLayout> 

AndroidManifest.xml

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

7. Enable Download Button:
   MainActivity.Java

if(Build.VERSION.SDK_INT>= Build.VERSION_CODES.M){
if(checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_DENIED){

            Log.d("permission","permission denied to WRITE_EXTERNAL_STORAGE - requesting it");
            String[] permissions = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
            requestPermissions(permissions,1);
        }


    }

//handle downloading

webview.setDownloadListener(new DownloadListener() {
@Override
public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimeType, long contentLength) {

            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
            request.setMimeType(mimeType);
            String cookies = CookieManager.getInstance().getCookie(url);
            request.addRequestHeader("cookie",cookies);
            request.addRequestHeader("User-Agent",userAgent);
            request.setDescription("Downloading file....");
            request.setTitle(URLUtil.guessFileName(url,contentDisposition,mimeType));
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS,URLUtil.guessFileName(url, contentDisposition, mimeType));
            DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
            dm.enqueue(request);
            Toast.makeText(getApplicationContext(),"Downloading File",Toast.LENGTH_SHORT).show();


        }
    });

AndroidMainfest.xml