Error Android Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'

Question

I have a fragment with button, on click the button should change the theme in my app but when i open the class i simply get this error: This is the logcat

08-14 21:32:45.914  29624-29624/addid E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: appid, PID: 29624
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at appid.Fragment.GuidaTv.InitView(GuidaTv.java:75)
        at appid.Fragment.GuidaTv.onCreateView(GuidaTv.java:41)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:955)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:740)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501)
        at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:458)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

My Class:

public class GuidaTv extends Fragment implements View.OnClickListener{

private Button FirstThemButton;
private Button SecondThemButton;
private Button ThirdThemButton;
private SharedPreferences sharePrefences;
private SharedPreferences.Editor editor;

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


    SharePreference();
    InitView();
    FirstThemButton =(Button) v.findViewById(R.id.FirstThem);
    SecondThemButton =(Button) v.findViewById(R.id.SecondThem);
    SecondThemButton =(Button) v.findViewById(R.id.ThirdThem);



    return v;
}


private void SharePreference() {
    sharePrefences=this.getActivity().getSharedPreferences("config", Context.MODE_WORLD_READABLE
            | Context.MODE_WORLD_WRITEABLE);
    editor=sharePrefences.edit();
    boolean isThem = sharePrefences.getBoolean("isThem", false);
    int Them = sharePrefences.getInt("Them",0);//config不存在时返回0
    if(isThem){
        if(Them==1){
            getActivity().setTheme(R.style.AppTheme2);
        }else if(Them==2){
            getActivity().setTheme(R.style.AppTheme2);
        }else if(Them==3){
            getActivity().setTheme(R.style.AppTheme2);
        }
    }else{//sharePrefences不存在是使用默认主题
        getActivity().setTheme(R.style.AppTheme);
    }
}

private void InitView() {
    FirstThemButton=(Button) getActivity().findViewById(R.id.FirstThem);
    SecondThemButton=(Button) getActivity().findViewById(R.id.SecondThem);
    ThirdThemButton=(Button) getActivity().findViewById(R.id.ThirdThem);
    FirstThemButton.setOnClickListener(this);
    SecondThemButton.setOnClickListener(this);
    ThirdThemButton.setOnClickListener(this);
}


public void onClick(View v) {
    switch (v.getId()) {
        case R.id.FirstThem:
            editor.putBoolean("isThem", true);
            editor.putInt("Them", 1);
            editor.commit();
            break;
        case R.id.SecondThem:
            editor.putBoolean("isThem", true);
            editor.putInt("Them",2);
            editor.commit();
            break;
        case R.id.ThirdThem:
            editor.putBoolean("isThem", true);
            editor.putInt("Them", 3);
            editor.commit();
            break;
        default:
            break;
    }

   }
}

my xml file:

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:background="#E5E5E5"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
    android:id="@+id/FirstThem"
    android:layout_width="10dp"
    android:layout_height="10dp"
    android:text="样式一"
    />

<Button
    android:id="@+id/SecondThem"
    android:layout_width="10dp"
    android:layout_height="10dp"
    android:text="样式二"
    />

<Button
    android:id="@+id/ThirdThem"
    android:layout_width="10dp"
    android:layout_height="10dp"
    android:text="样式三"
    />

Please help me to resolve the problem.

Solution 1

Where is your button located? In the activity or the fragments layout? Looks like you are trying to get it twice. Once from the activity inside InitView(); and then again inside onCreateView();

There lies your problem. If your XML layout is inflated from the activity use getActivity().findViewById(R.id.FirstThem);

If its inside the fragment layout, then use the view.findViewById(R.id.FirstThem);

Code Example:

public class GuidaTv extends Fragment implements View.OnClickListener{
 
private Button FirstThemButton;
private Button SecondThemButton;
private Button ThirdThemButton;
private SharedPreferences sharePrefences;
private SharedPreferences.Editor editor;
 
@Override 
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view =inflater.inflate(R.layout.guida_tv,container,false);
 
 
    SharePreference(); 

    FirstThemButton =(Button) view.findViewById(R.id.FirstThem);
    SecondThemButton =(Button) view.findViewById(R.id.SecondThem);

    ThirdThemButton =(Button) view.findViewById(R.id.ThirdThem);
    ^^^ This is the culprit! Change the name! 

    InitView();
 
    return view;
} 
 
 
private void SharePreference() { 
    sharePrefences=this.getActivity().getSharedPreferences("config", Context.MODE_WORLD_READABLE
            | Context.MODE_WORLD_WRITEABLE);
    editor=sharePrefences.edit();
    boolean isThem = sharePrefences.getBoolean("isThem", false);
    int Them = sharePrefences.getInt("Them",0);//config不存在时返回0
    if(isThem){
        if(Them==1){
            getActivity().setTheme(R.style.AppTheme2);
        }else if(Them==2){
            getActivity().setTheme(R.style.AppTheme2);
        }else if(Them==3){
            getActivity().setTheme(R.style.AppTheme2);
        } 
    }else{//sharePrefences不存在是使用默认主题 
        getActivity().setTheme(R.style.AppTheme);
    } 
} 
 
private void InitView() { 
    FirstThemButton.setOnClickListener(this);
    SecondThemButton.setOnClickListener(this);
    ThirdThemButton.setOnClickListener(this);
} 
 
 
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.FirstThem:
            editor.putBoolean("isThem", true);
            editor.putInt("Them", 1);
            editor.commit();
            break; 
        case R.id.SecondThem:
            editor.putBoolean("isThem", true);
            editor.putInt("Them",2);
            editor.commit();
            break; 
        case R.id.ThirdThem:
            editor.putBoolean("isThem", true);
            editor.putInt("Them", 3);
            editor.commit();
            break; 
        default: 
            break; 
    } 
 
} 

Solution 2

Try this.

create one onViewCreated view and place the setOnClickListener inside it.

example:

override fun onViewCreated(view: View, savedInstanceState: Bundle?) { 
    buttonName.setOnClickListener { 
        Toast.makeText(activity,"Success.", Toast.LENGTH_SHORT).show()
    }
}