findViewById Attribute in Fragment from the activity xml Not work

Question

How to access an attribute in the activity xml? I want to use it in fragment.

for example : this is my activity xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:fab="http://schemas.android.com/apk/res-auto">

<androidx.constraintlayout.widget.ConstraintLayout
    fab:layout_constraintTop_toTopOf="parent"
    fab:layout_constraintLeft_toLeftOf="parent"
    fab:layout_constraintRight_toRightOf="parent"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/layTitle"
    android:layoutDirection="rtl"
    android:background="@color/colorPrimary"
    android:padding="@dimen/paddingTitle"
    android:elevation="@dimen/elevationActivityTitle"
    android:layout_alignParentTop="true">
    <ImageView
        fab:layout_constraintLeft_toLeftOf="parent"
        fab:layout_constraintTop_toTopOf="parent"
        fab:layout_constraintBottom_toBottomOf="parent"
        android:layout_width="@dimen/imgActivityTitle"
        android:layout_height="@dimen/imgActivityTitle"
        android:id="@+id/btn_back"
        android:src="@drawable/ic_back"
        android:elevation="5dp"
        android:layout_alignParentEnd="true"
        android:layout_centerVertical="true"/>
    

</androidx.constraintlayout.widget.ConstraintLayout>
<FrameLayout
    android:id="@+id/frag"
    android:layout_width="0dp"
    android:layout_height="0dp"
    fab:layout_constraintBottom_toBottomOf="parent"
    fab:layout_constraintTop_toBottomOf="@+id/layTitle"
    fab:layout_constraintLeft_toLeftOf="parent"
    fab:layout_constraintRight_toRightOf="parent"
    />
</androidx.constraintlayout.widget.ConstraintLayout>

I want findViewByid ImageView in fragment When I was searching for solution I got the following one:

TextView btn_back= (TextView) getView().findViewById(R.id.btn_back)

But, unfortunately it was not working for me.

Where are you using this line? Activity or fragment? – Süleyman Bilgin Nov 11 '20 at 12:03 — Süleyman Bilgin, Nov 11 '20 at 12:03

score 1 · Answer 1 · answered Nov 11 '20 at 12:16

1

Use either viewModel or interfaces to talk between activity and fragment. don't try to send the button to fragment but trigger it from there. That will prevent any leaks or null pointers.

answered Nov 11 '20 at 12:16

Arutha

494
5
14

score 1 · Answer 2 · answered Nov 11 '20 at 12:17

Ok. You have some options.

Firstly, you can access these variables to directly in fragment like that.

MainActivity.java

TextView backButton;

backButton = findViewById(R.id.btn_back);

Fragment.java

((MainActivity) getActivity()).backButton

You can get current activity with getActivity() but Java compiler cannot understand which activity so have to cast to MainActivity.

Secondly, you can pass your activity instance to fragment. You can use constructors and newInstance() function. You can read that post Best practice for instantiating a new Android Fragment

In my opinion, I prefer second option because you guarantee these variables that include activity class. Some devices occur errors at first option. But second option uses more ram because you are passing your variables to another class.

The choice is yours

First option not work , i use it but crashed application maybe second way work so thank you for answer — Pouria Hemi, Nov 11 '20 at 12:33

score 1 · Accepted Answer · answered Nov 11 '20 at 18:24

1

You can use the interface to do it :

Create an interface names IBtnClick with one void method: "void onBtnClicked();"

use interface in activity like this:

IBtnClick iBtnClick= (IBtnClick)getActivity();

here getAtivity is our context, if it doesn't work use another scope context.

and use your method in button click listener like this

iBtnClick.onBtnClicked();

Now in your fragment you have to implements interface and

you can add any action you want in Overrided method.

answered Nov 11 '20 at 18:24

Hamed Karami

405
1
6
28

I want use in activity – Pouria Hemi Nov 12 '20 at 00:29
1

I know, you can use it in the activity. – Hamed Karami Nov 12 '20 at 07:11

score 0 · Answer 4 · answered Nov 11 '20 at 11:32

Try This code

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.recharge_plane_fragment, container, false);

  
    alertdialog_Listview=view.findViewById(R.id.alertdialog_Listview);

  

    return view;
}

score 0 · Answer 5 · answered Nov 11 '20 at 11:41

0

You can declare your TextView btn_back as static in activity

public static TextView btn_back;
btn_back = (TextView) findViewById(R.id.btn_back);

and get it in fragment

TextView btn_back = ((MainActivity)getActivity()).btn_back;

answered Nov 11 '20 at 11:41

Ann Developer

157
3

1

Making views static causes memory leaks. Also, what is the point of using a fragment if it only works in 1 specific Activity? – Elletlar Nov 11 '20 at 12:05

findViewById Attribute in Fragment from the activity xml Not work

5 Answers5