我想在 MainActivity 内部的一个片段中获取 EditText（来自 MainActivity），我得到一个 Nullpointer 错误

Question

Hello i want to get the EditText (from the MainActivity) in a fragment inside off the MainActivity and get this error "java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.addTextChangedListener(android.text.TextWatcher)' on a null object reference " and i dont know what to do..

Please help me. Thanks your EiskalterFreund

Error: "java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.addTextChangedListener(android.text.TextWatcher)' on a null object reference"

Code (fragment what calls the EditText):

EditText search;
search = view.findViewById(R.id.main_app_search);

XML File (MainActivity):

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:aapt="http://schemas.android.com/aapt"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mainLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        android:id="@+id/TabLayout">

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/main_tabs"
            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:layout_gravity="bottom"
            android:background="@drawable/common_google_signin_btn_icon_light_normal_background"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:tabIndicator="@color/white"
            app:tabIndicatorColor="@color/colorAccent"
            app:tabIndicatorHeight="2dp"
            app:tabSelectedTextColor="@color/colorAccent"
            app:tabTextColor="@color/design_default_color_on_secondary" />

    </LinearLayout>

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/AppBarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <include
            android:id="@+id/main_page_toolbar"
            layout="@layout/main_app_bar_layout" />

    </com.google.android.material.appbar.AppBarLayout>

    <EditText
        android:id="@+id/main_app_search"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:hint="Search..."
        android:layout_marginTop="60dp"/>

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/main_tabs__pager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/floating_button"
        android:layout_below="@+id/AppBarLayout">

    </androidx.viewpager.widget.ViewPager>

</RelativeLayout>

Answer 1

If you declared the edittext public you can access the edittext in fragment like this

MainActivity class

public EditText search;

//now initiate it with correct id in onCreate() method
onCreate(){
search = view.findViewById(R.id.main_app_search);
}

then in fragment class get the edittext like this

((MainActivity)getActivity()). search.setText("Hello")

Answer 2

You forgot to give your EditText an ID.