问题
My Main Activity. This is where all my coding is done.
FrameLayout simpleFrameLayout;
TabLayout tabLayout;
VideoView video;
Button btn_show;
InterstitialAd interstitialAd;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn_show = (Button) findViewById(R.id.bt_show);
interstitialAd = new InterstitialAd(this);
interstitialAd.setAdUnitId("ca-app-pub-8708219564656739/2401085524");
interstitialAd.loadAd(new AdRequest.Builder().build());
btn_show.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
interstitialAd.show();
}
});
// get the reference of FrameLayout and TabLayout
simpleFrameLayout = (FrameLayout) findViewById(R.id.simpleFrameLayout);
tabLayout = (TabLayout) findViewById(R.id.simpleTabLayout);
// Create a new Tab named "First"
TabLayout.Tab firstTab = tabLayout.newTab();
firstTab.setText("Apps"); // set the Text for the first Tab
firstTab.setIcon(R.drawable.app); // set an icon for the
// first tab
tabLayout.addTab(firstTab); // add the tab at in the TabLayout
// Create a new Tab named "Second"
TabLayout.Tab secondTab = tabLayout.newTab();
secondTab.setText("Products"); // set the Text for the second Tab
secondTab.setIcon(R.drawable.company); // set an icon for the second tab
tabLayout.addTab(secondTab); // add the tab in the TabLayout
// Create a new Tab named "Third"
TabLayout.Tab thirdTab = tabLayout.newTab();
thirdTab.setText("Donate"); // set the Text for the first Tab
thirdTab.setIcon(R.drawable.donation); // set an icon for the first tab
tabLayout.addTab(thirdTab); // add the tab at in the TabLayout
// perform setOnTabSelectedListener event on TabLayout
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
// get the current selected tab's position and replace the fragment accordingly
Fragment fragment = null;
switch (tab.getPosition()) {
case 0:
fragment = new FirstFragment();
break;
case 1:
fragment = new SecondFragment();
break;
case 2:
fragment = new ThirdFragment();
break;
}
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.simpleFrameLayout, fragment);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft.commit();
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
}
My Main Activity Xml.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center"
android:clickable="true"
android:focusable="true"
android:gravity="center"
android:orientation="vertical"
tools:context=".MainActivity">
<android.support.design.widget.TabLayout
android:id="@+id/simpleTabLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:tabBackground="@android:color/darker_gray"
app:tabIndicatorColor="#f00"
app:tabSelectedTextColor="#f00"
app:tabTextColor="#000" />
<FrameLayout
android:id="@+id/simpleFrameLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#9C27B0">
</FrameLayout>
</LinearLayout>
My Third Fragment XML. This is my third fragent and where my button is located.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/rellay"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#00BCD4"
tools:context="info.androidhive.materialtabs.fragments.OneFragment">
<Button
android:id="@+id/bt_show"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Show Ad"
android:textAllCaps="false" />
<com.google.android.gms.ads.AdView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/ad_view"
android:layout_centerHorizontal="true"
xmlns:ads="http://schemas.android.com/apk/res-auto"
ads:adSize="BANNER"
ads:adUnitId="ca-app-pub-8708219564656739/7492209225"/>
<com.google.android.gms.ads.AdView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/ad_view2"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
xmlns:ads="http://schemas.android.com/apk/res-auto"
ads:adSize="BANNER"
ads:adUnitId="ca-app-pub-8708219564656739/3552964218"/>
</RelativeLayout>
I am trying to use a button which is on my third layout to show a add and when I try to use my button in my MainActivity it gives me a null object error.
My Third Fragment Activity
package com.abhiandroid.tablayoutexample;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class ThirdFragment extends Fragment {
public ThirdFragment() {
// Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_third, container, false);
}
}
I need a method that searches other layouts for Id's as currently, my code is only searching the MainActitivity for Id's and hence is unable to find my button. This is a very small thing that is causing very large issues for me and is ruining my life slowly.
回答1:
try to pass that class object to the class where u are trying to access because no instance is available in memory and you are trying to access container without initialising so its giving u null issue.
回答2:
You are trying to access the button, which is defined in Third Fragment XML, from Main Activity which has activity_main.xml as its resource file. Android will try to search bt_show in activity_main.xml. Since it's not defined there, you are getting an NPE.
You should use findViewById method in the onCreateView or onViewCreated method of the Third Fragment.
Hope this helps.
来源：https://stackoverflow.com/questions/62662917/not-able-to-use-button-as-it-is-on-another-layout