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Ludiras
Asked: 2020-06-12 14:04:13 +0800 CST 2020-06-12 14:04:13 +0800 CST

Using Fragment and Activity with a Button Navigation View

  • 772

Goodnight everyone,

I have a button navigation view in my application that each button goes to a Fragment, except for the central button that I use to add and I want it to go to an Activity with a form, I have the following code:

package com.isaac.appet;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;

import com.isaac.appet.FinderFragment.FinderFragment;
import com.isaac.appet.HomeFragment.HomeFragment;
import com.isaac.appet.NotesFragment.NotesFragment;


public class MainActivity extends AppCompatActivity {

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

        BottomNavigationView bottomNavigation = findViewById(R.id.bottomNavigation);
        bottomNavigation.setOnNavigationItemSelectedListener(navListener);

        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.fragment_container,new HomeFragment()).commit();

    }

    private BottomNavigationView.OnNavigationItemSelectedListener navListener = new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {

            Fragment selectedFragment = null;


            switch (menuItem.getItemId()) {

                case R.id.btnHome:

                    selectedFragment = new HomeFragment();
                    break;

                case R.id.btnFinder:

                    selectedFragment = new FinderFragment();
                    break;

                case R.id.btnNotes:

                    selectedFragment = new NotesFragment();
                    break;

                case R.id.btnAdd:

                    startActivity(new Intent(MainActivity.this, PetsFormActivity.class));
                    break;
            }

            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, selectedFragment).commit();

            return true;
        }

    };

}

This is my attempt to make the central button go to the Activity, and in principle it does, but when I want to go back it gives me a Null Pointer, which I indicate below:

    2019-06-11 23:57:08.313 28899-28907/com.isaac.appet E/com.isaac.appe: Failed to send DDMS packet REAQ to debugger (-1 of 20): Broken pipe
2019-06-11 23:57:33.756 28899-28899/com.isaac.appet E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.isaac.appet, PID: 28899
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
        at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:396)
        at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:444)
        at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:434)
        at com.isaac.appet.MainActivity$1.onNavigationItemSelected(MainActivity.java:63)
        at android.support.design.widget.BottomNavigationView$1.onMenuItemSelected(BottomNavigationView.java:204)
        at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:840)
        at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:158)
        at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:991)
        at android.support.design.internal.BottomNavigationMenuView$1.onClick(BottomNavigationMenuView.java:115)
        at android.view.View.performClick(View.java:6597)
        at android.view.View.performClickInternal(View.java:6574)
        at android.view.View.access$3100(View.java:778)
        at android.view.View$PerformClick.run(View.java:25889)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6746)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:495)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

When I give it, it tells me that the line that is wrong or gives a conflict is the one that makes the Fragment transaction after the switch, but I'll stay there, to see if you can give me a hand. Thanks.

java

1 Answers

  1. Best Answer

    What you can do would be to create a method to load the fragments and not return null when selecting the Itemto load your activity:

    private void loadFragment(Fragment fragment) {
        // Cargar Fragmentos
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.frame_container, fragment);
        transaction.addToBackStack(null);
        transaction.commit();
    }

    Inside the case call the method and assign the fragment to load.

    Example:

    selectedFragment = new HomeFragment(); 
loadFragment(selectedFragment);

    To launch your activity it will be:

    case R.id.btnAdd:
startActivity(new Intent(MainActivity.this, PetsFormActivity.class));
break;

    Delete this line that is before thereturn true getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, selectedFragment).commit();

    • 3