Styjun

I have created android app using WebView

Functionality is working fine and But when i add private void createDialog() to showing alertdialog then whosing this error :

NullPointerException: Attempt to invoke virtual method 'void
android.app.Dialog.show()'

on a null object reference in Logcat

Here is my fragment code :

public class MainActivity extends AppCompatActivity
 implements NavigationView.OnNavigationItemSelectedListener 

 public Dialog mDialog;
 public Button mDialogyes, mDialogno;

 ProgressBar progressBar;
 WebView webView;

 @Override
 protected void onCreate(Bundle savedInstanceState) 
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
 setSupportActionBar(toolbar);

 progressBar = (ProgressBar) findViewById(R.id.progressBar);
 webView=(WebView) findViewById(R.id.webView);

 webView.setVisibility(View.INVISIBLE);
 webView.loadUrl("http://m.jazz.com.pk/smart/wifi_3g.html");
 WebSettings webSettings=webView.getSettings();
 webSettings.setJavaScriptEnabled(true);
 webView.setWebChromeClient(new WebChromeClient());

 webView.setWebViewClient(new WebViewClient() 
 @Override
 public void onPageStarted(WebView view, String url, Bitmap favicon) 
 super.onPageStarted(view, url, favicon);
 setProgressBarVisibility(View.VISIBLE);
 

 @Override
 public void onPageFinished(WebView view, String url) 
 super.onPageFinished(view, url);
 setProgressBarVisibility(View.GONE);
 webView.setVisibility(View.VISIBLE);
 

 @Override
 public void onReceivedError(WebView view, WebResourceRequest request, WebResourceError error) 
 super.onReceivedError(view, request, error);
 setProgressBarVisibility(View.GONE);
 
 );
 webView.loadUrl("http://m.jazz.com.pk/smart/wifi_3g.html");


 FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
 fab.setOnClickListener(new View.OnClickListener() 
 @Override
 public void onClick(View view) 


 
 );

 DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
 ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
 this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
 drawer.addDrawerListener(toggle);
 toggle.syncState();

 NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
 navigationView.setItemIconTintList(null);
 navigationView.setNavigationItemSelectedListener(this);

 ConnectivityManager cm = (ConnectivityManager) getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
 NetworkInfo activenetnetwork = cm.getActiveNetworkInfo();
 if(activenetnetwork != null)
 
 if(activenetnetwork.getType() == ConnectivityManager.TYPE_WIFI)
 
 //Toast.makeText(getApplicationContext(),activenetnetwork.getTypeName(),Toast.LENGTH_LONG).show();
 else if(activenetnetwork.getType() == ConnectivityManager.TYPE_MOBILE)
 
 //Toast.makeText(getApplicationContext(),activenetnetwork.getTypeName(),Toast.LENGTH_LONG).show();
 
 else 

 ActionBar actionBar = getSupportActionBar();
 actionBar.setTitle("Web page not available");
 Toast.makeText(getApplicationContext(),"Please Check your Internet ",Toast.LENGTH_LONG).show();
 


 

 private void setProgressBarVisibility(int visibility) 
 // If a user returns back, a NPE may occur if WebView is still loading a page and then tries to hide a ProgressBar.
 if (progressBar != null) 
 progressBar.setVisibility(visibility);
 
 

 private void createDialog() 
 mDialog = new Dialog(this);
 mDialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
 mDialog.setContentView(R.layout.dialog_exit);
 mDialog.setCanceledOnTouchOutside(true);
 mDialog.setCancelable(true);
 mDialogyes = (Button) mDialog.findViewById(R.id.yes);
 mDialogno = (Button) mDialog.findViewById(R.id.no);



 mDialogyes.setOnClickListener(new View.OnClickListener() 
 @Override
 public void onClick(View v) 
 Intent intent = new Intent(Intent.ACTION_MAIN);
 intent.setFlags(intent.FLAG_ACTIVITY_CLEAR_TOP);
 intent.addCategory(Intent.CATEGORY_HOME);
 startActivity(intent);
 finish();
 System.exit(0);


 

 );

 mDialogno.setOnClickListener(new View.OnClickListener() 
 @Override
 public void onClick(View v) 
 mDialog.dismiss();
 
 );


 
 @Override
 public void onBackPressed() 
 DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
 if (drawer.isDrawerOpen(GravityCompat.START)) 
 drawer.closeDrawer(GravityCompat.START);
 else 
 mDialog.show();
 

 

 @Override
 public boolean onCreateOptionsMenu(Menu menu) 
 // Inflate the menu; this adds items to the action bar if it is present.
 getMenuInflater().inflate(R.menu.main, menu);
 return true;
 

 @Override
 public boolean onOptionsItemSelected(MenuItem item) 
 // Handle action bar item clicks here. The action bar will
 // automatically handle clicks on the Home/Up button, so long
 // as you specify a parent activity in AndroidManifest.xml.
 int id = item.getItemId();

 //noinspection SimplifiableIfStatement
 if (id == R.id.action_settings) 
 return true;
 

 return super.onOptionsItemSelected(item);
 

 @SuppressWarnings("StatementWithEmptyBody")
 @Override
 public boolean onNavigationItemSelected(MenuItem item) 
 // Handle navigation view item clicks here.
 int id = item.getItemId();

 if (id == R.id.home) 


 else if (id == R.id.contact) 

 else if (id == R.id.about) 

 else if (id == R.id.share) 

 else if (id == R.id.rate) 

 else if (id == R.id.more) 

 

 DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
 drawer.closeDrawer(GravityCompat.START);
 return true;
 

Looking at your code, the method createDialog() is never called, so the value of mDialog is always null. You need to initialize the dialog (i.e. by calling createDialog()) before you can call mDialog.show(); in your onBackPressed() override.

Need a null pointer check before calling the show method. Example:

if (mDialog != null) 
 mDialog.show(); 

As commented above, your mDialog is null because you need to call the createDialog method first. Whatever code you copied from another application missed something.