How to go from one fragment to another, from an other java class?

Question

I have a login page on fragment connected to BackgroundWorker class which has database connectivity.

my login page sends texts from EditTexts to BackgroundWorker Class, then all the database queries(by accessing PHP files from WAMP) are done in the BackgroundWorker class.

When i click the login button on my fragment it opens the dialog box which tells me if login was successful or not. (the code of dialog box exists in BackgroundWorker class (Please refer the code if i am not being clear) )

but the thing is, i don't want dialog box, i want to go from one fragment to another from that BackgroundWorker.java file.

i have the code of how can i go from one activity to another, but not of fragment

fragment XML FILE

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="com.example.admin.blingiton.Client_login">

    <!-- TODO: Update blank fragment layout -->

    <RelativeLayout
        android:id="@+id/ClientLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    <ImageView
        android:id="@+id/back"
        android:layout_width="wrap_content"
        android:layout_height="600dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:scaleType="fitXY"
        app:srcCompat="@drawable/back" />

    <ImageView
        android:id="@+id/mirae"
        android:layout_width="300dp"
        android:layout_height="250dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:layout_marginBottom="12dp"
        android:layout_marginStart="32dp"
        android:scaleType="centerInside"
        app:srcCompat="@drawable/mirae" />

    <ImageView
        android:id="@+id/header"
        android:layout_width="wrap_content"
        android:layout_height="600dp"
        android:layout_alignBottom="@+id/mirae"
        android:layout_alignParentStart="true"
        android:layout_marginBottom="20dp"
        android:scaleType="fitStart"
        app:srcCompat="@drawable/header" />

    <EditText
        android:id="@+id/cusername"
        android:layout_width="200dp"
        android:layout_height="35dp"
        android:layout_alignTop="@+id/mirae"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="13dp"
        android:background="@drawable/username"
        android:ems="10"
        android:hint="username"
        android:inputType="textPersonName"
        android:textAlignment="center" />

    <EditText
        android:id="@+id/cpassword"
        android:layout_width="200dp"
        android:layout_height="35dp"
        android:layout_alignStart="@+id/cusername"
        android:layout_below="@+id/cusername"
        android:layout_marginTop="18dp"
        android:background="@drawable/password"
        android:ems="10"
        android:hint="password"
        android:inputType="textPassword"
        android:textAlignment="center" />

    <Button
        android:id="@+id/clogin"
        android:layout_width="200dp"
        android:layout_height="35dp"
        android:layout_above="@+id/signupbtn"
        android:layout_alignStart="@+id/cpassword"
        android:layout_marginBottom="11dp"
        android:background="@drawable/login" />

    <Button
        android:id="@+id/signupbtn"
        android:layout_width="200dp"
        android:layout_height="35dp"
        android:layout_alignBottom="@+id/mirae"
        android:layout_alignStart="@+id/clogin"
        android:background="@drawable/signup"
         />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:src="@drawable/log" />

    </RelativeLayout>
    <RelativeLayout
        android:id="@+id/afterlogin"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </RelativeLayout>

    </RelativeLayout>

Fragment.java file

EditText UsernameEt, PasswordEt;
Button login;
View v;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
    Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    v = inflater.inflate(R.layout.fragment_clientlogin, container, false);

    UsernameEt = (EditText) v.findViewById(R.id.cusername);
    PasswordEt = (EditText) v.findViewById(R.id.cpassword);
    login = (Button) v.findViewById(R.id.clogin);

    login.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        String username = UsernameEt.getText().toString();
        String password = PasswordEt.getText().toString();
        String type = "login";
        BackgroundWorker backgroundWorker = new
        BackgroundWorker(getActivity());
        backgroundWorker.execute(type, username, password);

      }
    });

    return v;
  }

BackgroundWorker.java < /b>

Context context;
AlertDialog alertDialog;
BackgroundWorker(Context ctx) {
  context = ctx;
}
@Override
protected String doInBackground(String...params) {
    String type = params[0];
    String login_url = "http://192.168.10.2/login.php";
    if (type.equals("login")) {
      try {
        String user_name = params[1];
        String password = params[2];
        URL url = new URL(login_url);
        HttpURLConnection httpURLConnection =
          (HttpURLConnection) url.openConnection();
        httpURLConnection.setRequestMethod("POST");
        httpURLConnection.setDoOutput(true);
        httpURLConnection.setDoInput(true);
        OutputStream outputStream = httpURLConnection.getOutputStream();
        BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
        String post_data = URLEncoder.encode("user_name", "UTF- 
          8 ")+" = "+URLEncoder.encode(user_name,"
          UTF - 8 ")+" & " +
          URLEncoder.encode("password", "UTF- 
            8 ")+" = "+URLEncoder.encode(password,"
            UTF - 8 ");
            bufferedWriter.write(post_data); 
            bufferedWriter.flush(); 
            bufferedWriter.close(); 
            outputStream.close(); 
            InputStream inputStream = httpURLConnection.getInputStream(); 
            BufferedReader bufferedReader = new BufferedReader(new 
            InputStreamReader(inputStream, "iso-8859-1")); 
            String result = ""; String line = "";
            while ((line = bufferedReader.readLine()) != null) {
              result += line;
            }
            bufferedReader.close(); inputStream.close(); httpURLConnection.disconnect();
            return result;
          }
          catch (MalformedURLException e) {
            e.printStackTrace();
          } catch (IOException e) {
            e.printStackTrace();
          }
        }
        return null;
      }

      @Override
      protected void onPreExecute() {
        alertDialog = new AlertDialog.Builder(context).create();
        alertDialog.setTitle("Login Status");
      }

      @Override
      protected void onPostExecute(String result) {
        Client_login cl = new Client_login();

        alertDialog.setMessage(result);
        //alertDialog.show();
        if (result.contentEquals("login success !!!!! Welcome user")) {


          //Code Here.

        } else {
          Toast toast = Toast.makeText(context, "Email or password is wrong",
            Toast.LENGTH_SHORT);
          toast.show();
        }
      }

      @Override
      protected void onProgressUpdate(Void...values) {
        super.onProgressUpdate(values);
      }

Possible duplicate of [How to go to fragment from activity](https://stackoverflow.com/questions/18011374/how-to-go-to-fragment-from-activity) — Bhuvanesh BS, Apr 23 '18 at 17:28

Rishabh Rawat · Answer 1 · 2018-04-23T18:23:21.330

try to use this if you find any error please let me know. First create a interface

interface ChangeFragment
{
   public void chfragment();
}

Then your second fragment

public class SecondFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// this is your success login fragment
return inflater.inflate(R.layout.fragment_second, container, false);
 }
}

After that your activity where you place the login fragment

public class Successfull extends Activity implements ChangeFragment
{
     protected void onCreate(android.os.Bundle savedInstanceState) {

      //your code    
     }  
    }

    @Override
    public void chfragment()
    {
        SecondFragment yoursecondfragment=new SecondFragment();
        FragmentManager manager=getSupportedFragmentManager();
        FragmentTransaction transaction=manager.beginTransaction();
        transaction.replace(R.layout.framelayout,yoursecondfragment);
        transaction.commit();
    }
}

then your backgroundworker thread

Context context;
    AlertDialog alertDialog;
    BackgroundWorker (Context ctx) {
        context = ctx;
    }
    @Override
    protected String doInBackground(String... params) {
        String type = params[0];
        String login_url = "http://192.168.10.2/login.php";
        if(type.equals("login")) {
            try {
                String user_name = params[1];
                String password = params[2];
                URL url = new URL(login_url);
                HttpURLConnection httpURLConnection = 
    (HttpURLConnection)url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);
                OutputStream outputStream = httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter = new BufferedWriter(new 
    OutputStreamWriter(outputStream, "UTF-8"));
                String post_data = URLEncoder.encode("user_name","UTF- 
   8")+"="+URLEncoder.encode(user_name,"UTF-8")+"&"
                        +URLEncoder.encode("password","UTF- 
   8")+"="+URLEncoder.encode(password,"UTF-8");
                bufferedWriter.write(post_data);
                bufferedWriter.flush();
                bufferedWriter.close();
                outputStream.close();
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new 
   InputStreamReader(inputStream,"iso-8859-1"));
                String result="";
                String line="";
                while((line = bufferedReader.readLine())!= null) {
                    result += line;
                }
                bufferedReader.close();
                inputStream.close();
                httpURLConnection.disconnect();
                return result;
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override
    protected void onPreExecute() {
        alertDialog = new AlertDialog.Builder(context).create();
        alertDialog.setTitle("Login Status");
    }

    @Override
    protected void onPostExecute(String result) {
        Client_login cl = new Client_login();

        alertDialog.setMessage(result);
        //alertDialog.show();
        if(result.contentEquals("login success !!!!! Welcome user")) {
           //Code Here.
           ChangeFragment frag=new Successfull();
           frag.chfragment();

        }else
        {
            Toast toast= Toast.makeText(context, "Email or password is wrong", 
    Toast.LENGTH_SHORT);
            toast.show();
        }
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }

I think this code will help you.

.FragmentManager android.support.v4.app.FragmentActivity.getSupportFragmentManager()' on a null object reference i got this error, i dont want to go from an activity, i want to go from interface to activity. — Parisa Sachdev, Apr 28 '18 at 14:29

How to go from one fragment to another, from an other java class?

1 Answers1