Develop Reference

Empty Exposed Dropdown menu when placed inside a custom dialog layout

I'm trying to implement an Exposed Dropdown menu on an AlertDialog with a custom layout defined in dialog_main_createremote.xml:
<?xml version="1.0" encoding="utf-8"?>
<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="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
android:padding="10dp">
<com.google.android.material.textfield.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Name"
style="#style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
android:layout_marginTop="10dp">
<com.google.android.material.textfield.TextInputEditText
android:id="#+id/dialog_main_textinput"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</com.google.android.material.textfield.TextInputLayout>
<com.google.android.material.textfield.TextInputLayout
style="#style/Widget.MaterialComponents.TextInputLayout.OutlinedBox.ExposedDropdownMenu"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:hint="Category">
<AutoCompleteTextView
android:id="#+id/dialog_main_dropdown"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:inputType="none"/>
</com.google.android.material.textfield.TextInputLayout>
</LinearLayout>
As per Material Design Guidelines, items need a layout for the dropdown menu to appear, so I created the following in the dropdown_item.xml file:
<?xml version="1.0" encoding="utf-8"?>
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="16dp"
android:ellipsize="end"
android:maxLines="1"
android:textAppearance="?attr/textAppearanceSubtitle1" />
Finally, I started to generate the AlertDialog with a MaterialAlertDialogBuilder, then defined and instantiated a LayoutInflater which I used to get dialog's custom view and get access to the setAdapter method, but after setting the adapter and showing the dialog all I can get is an Outlined TextInputLayout without any dropdown menu.
So that's it, thanks in advance for any suggestions/solutions, also, as you may have noticed, I'm new to android development, so, if possible and of course, if you have time in your hands, elaborate your answer or point to a specific resource where I could get more info.
MainActivity.java:
public class MainActivity extends AppCompatActivity {
private RemoteListViewModel remoteListViewModel;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RecyclerView recyclerView = findViewById(R.id.main_recyclerview);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setHasFixedSize(true);
final RemoteAdapter adapter = new RemoteAdapter();
recyclerView.setAdapter(adapter);
remoteListViewModel = new ViewModelProvider(this).get(RemoteListViewModel.class);
remoteListViewModel.getAllRemotes().observe(this, new Observer<List<Remote>>() {
#Override
public void onChanged(#Nullable List<Remote> remotes) {
adapter.setRemotes(remotes);
}
});
ExtendedFloatingActionButton createButton = findViewById(R.id.create_efab);
createButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
MaterialAlertDialogBuilder builder = new MaterialAlertDialogBuilder(MainActivity.this);
LayoutInflater inflater = LayoutInflater.from(MainActivity.this);
final View inflatedView = inflater.inflate(R.layout.dialog_main_createremote, null);
AutoCompleteTextView actv = inflatedView.findViewById(R.id.dialog_main_dropdown);
String categories[] = getResources().getStringArray(R.array.categories);
actv.setAdapter(new ArrayAdapter(MainActivity.this, R.layout.dropdown_item, categories));
builder.setView(R.layout.dialog_main_createremote);
builder.setTitle("Set control params");
builder.setNegativeButton("Nope", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
builder.setPositiveButton("Okey", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
builder.show();
}
});
}
}

why setOnClickListener doesnt work in my view pager?

I have a view pager and cardview in my activity
and define lottie animation for my favorite btn
but the code of setOnClickListener didnt work and app did crash when i go to this activity
when i comment the setOnClickListener code, it will ok
and also the code is working well in another activity
this is my java activity code
public class MainActivity3 extends AppCompatActivity {
ImageView imageView;
String[] money;
boolean switchIsOn = false;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main3);
//favorite animation button
final LottieAnimationView animatedSwitchButton =(LottieAnimationView) findViewById(R.id.fav_lot);
animatedSwitchButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (switchIsOn){
animatedSwitchButton.setSpeed(-1);
animatedSwitchButton.playAnimation();
switchIsOn = false;
}else {
animatedSwitchButton.setSpeed(1);
animatedSwitchButton.playAnimation();
switchIsOn = true;
}
}
});
money = getResources().getStringArray(R.array.money);
ViewPager mViewPager = findViewById(R.id.viewPager);
CardPagerAdapters mCardAdapter = new CardPagerAdapters();
for (String s : money) {
mCardAdapter.addCardItem(new CardItemString(s));
}
mViewPager.setAdapter(mCardAdapter);
mViewPager.setOffscreenPageLimit(3);
}
}
and the adapter.xml
<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.card.MaterialCardView 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:id="#+id/cardView"
android:layout_width="250dp"
android:layout_height="320dp"
app:cardCornerRadius="20dp"
android:layout_gravity="center"
android:backgroundTint="#00FFFFFF">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#6FCDDC39"
android:padding="15dp">
<TextView
android:id="#+id/titleTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_alignParentEnd="true"
android:layout_gravity="center_horizontal"
android:fontFamily="sans-serif-black"
android:gravity="center_horizontal"
android:text="#string/app_name"
android:textColor="#075AFF"
android:textSize="24sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.airbnb.lottie.LottieAnimationView
android:id="#+id/fav_lot"
android:layout_width="100dp"
android:layout_height="100dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.533"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/titleTextView"
app:lottie_rawRes="#raw/fav" />
</androidx.constraintlayout.widget.ConstraintLayout>
</com.google.android.material.card.MaterialCardView>
the logcat error is
2020-11-24 16:47:40.817 11330-11330/com.paradise.myapplication4 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.paradise.myapplication4, PID: 11330
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.paradise.myapplication4/com.paradise.myapplication4.MainActivity3}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.airbnb.lottie.LottieAnimationView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.airbnb.lottie.LottieAnimationView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.paradise.myapplication4.MainActivity3.onCreate(MainActivity3.java:26)
at android.app.Activity.performCreate(Activity.java:7009)
at android.app.Activity.performCreate(Activity.java:7000)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6494) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 
mainActivity.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
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"
tools:context=".MainActivity">
<androidx.viewpager.widget.ViewPager
android:id="#+id/viewPager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"
android:overScrollMode="never"
android:paddingVertical="100dp"
android:paddingHorizontal="30dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0"/>
</RelativeLayout>
cardIPagerAdapter java code
public class CardPagerAdapters extends PagerAdapter {
private final List<CardView> mViews;
private final List<CardItemString> mData;
private float mBaseElevation;
public CardPagerAdapters() {
mData = new ArrayList<>();
mViews = new ArrayList<>();
}
public void addCardItem(CardItemString item) {
mViews.add(null);
mData.add(item);
}
public int getCount() {
return mData.size();
}
#Override
public boolean isViewFromObject(#NonNull View view, #NonNull Object object) {
return view == object;
}
#NonNull
#Override
public Object instantiateItem(ViewGroup container, int position) {
View view = LayoutInflater.from(container.getContext())
.inflate(R.layout.adapter, container, false);
container.addView(view);
bind(mData.get(position), view);
CardView cardView = view.findViewById(R.id.cardView);
if (mBaseElevation == 0) {
mBaseElevation = cardView.getCardElevation();
}
cardView.setMaxCardElevation(mBaseElevation * 1);
mViews.set(position, cardView);
return view;
}
#Override
public void destroyItem(ViewGroup container, int position, #NonNull Object object) {
container.removeView((View) object);
mViews.set(position, null);
}
private void bind(CardItemString item, View view) {
TextView titleTextView = view.findViewById(R.id.titleTextView);
titleTextView.setText(item.getTitle());
}
}

Your animatedSwitchButton is null because you use findViewById() on your current object, which is your MainActivity3. This Activity doesn't contain the View with the ID fav_lot in adapter.xml though, since its layout-file is set to activity_main3.xml.
So you need to use findViewById() on the object you attached your adapter.xml to. This could be mViewPager.findViewById(R.id.fav_lot) for example, although I am not sure what your adapter.xml is actually attached to.

RecyclerView has no LayoutManager android.support.v7.widget.RecyclerView

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.liliyu.easyresumebuilder, PID: 11145
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.liliyu.easyresumebuilder/com.example.liliyu.easyresumebuilder.MainActivity}: android.view.InflateException: Binary XML file line #10: RecyclerView has no LayoutManager android.support.v7.widget.RecyclerView{df7f7c9 VFED..... ......I. 0,0-0,0 #7f070061 app:id/main_activity1}, adapter:null, layout:null, context:com.example.liliyu.easyresumebuilder.MainActivity#2857d33
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2434)
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView
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"
android:id="#+id/main_activity1"
tools:context="com.example.liliyu.easyresumebuilder.MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="#dimen/spacing_medium"
android:orientation="vertical">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<LinearLayout
android:id="#+id/user_name_layout"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="#dimen/spacing_small"
android:layout_alignParentLeft="true"
android:layout_toLeftOf="#+id/user_picture"
android:gravity="center_vertical">
<TextView
android:id="#+id/name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="#dimen/caption_text_size"
tools:text="Your name" />
</LinearLayout>
<TextView
android:id="#+id/email"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/user_name_layout"
android:layout_toLeftOf="#+id/user_picture"
tools:text="Your email" />
</RelativeLayout>
</LinearLayout>
</android.support.v7.widget.RecyclerView>
MainActivity.java
#SuppressWarnings("ConstantConditions")
public class MainActivity extends AppCompatActivity {
private BasicInfo basicInfo;
private RecyclerView recyclerView = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
loadData();
setupUI();
}
private void setupUI() {
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.main_activity1);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
setupBasicInfo();
}
private void setupBasicInfo() {
((TextView) findViewById(R.id.name)).setText(TextUtils.isEmpty(basicInfo.name)
? "Your name"
: basicInfo.name);
((TextView) findViewById(R.id.email)).setText(TextUtils.isEmpty(basicInfo.email)
? "Your email"
: basicInfo.email);
ImageView userPicture = (ImageView) findViewById(R.id.user_picture);
if (basicInfo.imageUri != null) {
ImageUtils.loadImage(this, basicInfo.imageUri, userPicture);
} else {
userPicture.setImageResource(R.drawable.user_ghost);
}
findViewById(R.id.edit_basic_info).setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, BasicInfoEditActivity.class);
intent.putExtra(BasicInfoEditActivity.KEY_BASIC_INFO, basicInfo);
startActivityForResult(intent, REQ_CODE_EDIT_BASIC_INFO);
}
});
}
private void loadData() {
connectAndGetApiData();
basicInfo = basicInfo == null ? new BasicInfo() : basicInfo;
}
public void connectAndGetApiData() {
if (retrofit == null) {
retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build();
}
ResumeService resumeService=retrofit.create(ResumeService.class);
Call<Resume> call =resumeService.getResume();
try {
call.enqueue(new Callback<Resume>() {
#Override
public void onResponse(Call<Resume> call, Response<Resume> response) {
recyclerView.setAdapter(new ResumeAdapter(getApplicationContext(),response.body()));
}
#Override
public void onFailure(Call<Resume> call, Throwable throwable) {
System.out.println(throwable.toString());
}
});
}catch(Throwable e){
e.printStackTrace();
}
}
}

Add a parentLayout (could be LinearLayout) to your RecyclerView and remove child from your RecyclerView.

You can't put children inside a RecyclerView in XML. It looks like what you have there currently is what you want to be in your ViewHolder. That's not how to do it.
Make a new layout XML file and move what's wrapped in your RecyclerView into that file.
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/main_activity1"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
//delete all elements
</android.support.v7.widget.RecyclerView
>

java.lang.NullPointerException error in GridView making app crash

I created a 2x2 grid where the first 3 grids has three(Thingspeak) charts imported from GitHub(https://github.com/MacroYau/ThingSpeakAndroid)and the fourth grid will be implemented later so for the time being I just added a blank chart in it.
I have checked out all similar questions on stackoverflow and read their answers and I have understood the error in the logcat at line 60(chartView = (LineChartView) findViewById(R.id.chart);) means that this id is pointing to null but I don't know how to solve it as chart is present as an id in my activity_main.xml layout.
I have used the following files: activity_main.xml, main.xml, TempHumidity.java and GridViewAdapter.java
Code snippet from TempHumidity.java
public class TempHumidity extends AppCompatActivity {
private ThingSpeakChannel tsChannel, tsChannel1, tsChannel2;
private ThingSpeakLineChart tsChart, tsChart1, tsChart2;
private LineChartView chartView, chartView1, chartView2;
GridView simpleGrid;
int charts[] = {R.id.chart, R.id.chart1, R.id.chart2};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
simpleGrid = (GridView) findViewById(R.id.simpleGridView); // init GridView
// Create an object of CustomAdapter and set Adapter to GirdView
GridViewAdapter customAdapter = new GridViewAdapter(getApplicationContext(), charts);
simpleGrid.setAdapter(customAdapter);
// Connect to ThinkSpeak Channels
tsChannel = new ThingSpeakChannel(377467);
tsChannel1 = new ThingSpeakChannel(357670);
tsChannel2 = new ThingSpeakChannel(377509);
// Set listener for Channel feed update events
tsChannel.setChannelFeedUpdateListener(new ThingSpeakChannel.ChannelFeedUpdateListener() {
#Override
public void onChannelFeedUpdated(long channelId, String channelName, ChannelFeed channelFeed) {
// Show Channel ID and name on the Action Bar
getSupportActionBar().setTitle(channelName);
getSupportActionBar().setSubtitle("Channel " + channelId);
// Notify last update time of the Channel feed through a Toast message
Date lastUpdate = channelFeed.getChannel().getUpdatedAt();
Toast.makeText(TempHumidity.this, lastUpdate.toString(), Toast.LENGTH_LONG).show();
}
});
// Fetch the specific Channel feed
tsChannel.loadChannelFeed();
// Create a Calendar object dated 1 minutes ago
Calendar calendar = Calendar.getInstance();
calendar.add(Calendar.MINUTE, -1);
// Configure LineChartView
chartView = (LineChartView) findViewById(R.id.chart); //Logcat error points here
chartView.setZoomEnabled(false);
chartView.setValueSelectionEnabled(true);
GridViewAdapter.java
public class GridViewAdapter extends BaseAdapter {
private Context context;
private final int[] charts;
LayoutInflater inflter;
public GridViewAdapter(Context Appcontext, int[] charts) {
this.context = Appcontext;
this.charts = charts;
inflter = (LayoutInflater.from(Appcontext));
}
#Override
public View getView(int i, View view, ViewGroup viewGroup) {
view = inflter.inflate(R.layout.activity_main, null); // inflate the layout
LineChartView cv = (LineChartView) view.findViewById(R.id.chart); // get the reference of ImageView
return view;
}
#Override
public int getCount() {
return charts.length;
}
#Override
public Object getItem(int position) {
return null;
}
#Override
public long getItemId(int position) {
return 0;
}
}
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<!--
-->
<GridView
android:id="#+id/simpleGridView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:footerDividersEnabled="false"
android:padding="1dp"
android:numColumns="2" />
</LinearLayout>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<!-- Container LinearLayout -->
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<!-- Row 1 -->
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1">
<lecho.lib.hellocharts.view.LineChartView
android:id="#+id/chart"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
/>
<lecho.lib.hellocharts.view.LineChartView
android:id="#+id/chart1"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
/>
</LinearLayout>
<!-- Row 2 -->
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1">
<lecho.lib.hellocharts.view.LineChartView
android:id="#+id/chart2"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
/>
<lecho.lib.hellocharts.view.LineChartView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
/>
</LinearLayout>
</LinearLayout>
Logcat:
E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.macroyau.thingspeakandroid.demo/com.macroyau.thingspeakandroid.demo.TempHumidity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2299)
at android.app.ActivityThread.access$700(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5283)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.macroyau.thingspeakandroid.demo.TempHumidity.onCreate(TempHumidity.java:60)
at android.app.Activity.performCreate(Activity.java:5283)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2299) 
at android.app.ActivityThread.access$700(ActivityThread.java:150) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:5283) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869) 
at dalvik.system.NativeStart.main(Native Method) 
01-14 17:11:28.007 23142-23146/com.macroyau.thingspeakandroid.demo
D/dalvikvm: GC_CONCURRENT freed 587K, 19% free 8887K/10932K, paused 4ms+22ms, total 114ms
When I run the codes(as it is in GitHub) without adding two similar charts in a GridView:
Currently my activity_main.xml layout looks like this:

As Mike M. in the comments pointed out that the chart id is not present in the main.xml file which is the reason why it pointing to null.
All I had to do is remove the main.xml file and set the layout to activity_main.xml in the onCreate method like this:
setContentView(R.layout.activity_main) (as I have already made a 2x2 layout in it activity_main.xml)
and remove the GridViewAdapter.java.

Navigation drawer header textview nullpointerexception

I have an 2 activity and a service, in first I have navigation drawer, and 2 textviews in its header, and I must change their text sometimes, in service there is some data that i need
On first run everything is perfect, but when I go to the first activity from second, I have nullpointerexception in textviews. What causes it, and how to fix?
//First
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Navigation drawer init
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbarMain);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view_main);
navigationView.setNavigationItemSelectedListener(this);
intent = new Intent("playbackservice");
sConn = new ServiceConnection() {
public void onServiceConnected(ComponentName name, IBinder binder) {
Log.d(LOG_TAG, "MainActivity onServiceConnected");
service = ((PlaybackService.PlaybackServiceBinder) binder).getService();
bound = true;
prepareLayout();
}
public void onServiceDisconnected(ComponentName name) {
Log.d(LOG_TAG, "MainActivity onServiceDisconnected");
bound = false;
}
};
}
private void prepareLayout() {
Log.d(LOG_TAG, "prepareLayout: Running");
((TextView) findViewById(R.id.songNameNavhead)).setText(currentSong.getName());
((TextView) findViewById(R.id.artistNavhead)).setText(currentSong.getArtist());
}
And
//Layout nav_header_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="#dimen/nav_header_height"
android:gravity="bottom"
android:orientation="vertical"
android:background="#color/colorPrimaryDark"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:theme="#style/ThemeOverlay.AppCompat.Dark">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="#string/default_song_name"
android:id="#+id/songNameNavhead"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/default_artist"
android:id="#+id/artistNavhead"/>
</LinearLayout>
And
//activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
android:id="#+id/drawer_layout"
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:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="#layout/app_bar_main"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<android.support.design.widget.NavigationView
android:id="#+id/nav_view_main"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="#layout/nav_header_main"
app:menu="#menu/activity_main_drawer"/>
</android.support.v4.widget.DrawerLayout>
Error
05-12 19:34:05.001 11086-11086/iskandarovlev.myitschool.ru.lyricplayer E/AndroidRuntime: FATAL EXCEPTION: main
Process: iskandarovlev.myitschool.ru.lyricplayer, PID: 11086
java.lang.NullPointerException
//MainActivity.java:302 is
//((TextView) header.findViewById(R.id.songNameNavhead)).setText(currentSong.getName());
//this line
at iskandarovlev.myitschool.ru.lyricplayer.MainActivity.prepareLayout(MainActivity.java:302)
at iskandarovlev.myitschool.ru.lyricplayer.MainActivity.access$700(MainActivity.java:48)
at iskandarovlev.myitschool.ru.lyricplayer.MainActivity$3.onServiceConnected(MainActivity.java:355)
at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1140)
at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1157)
at android.os.Handler.handleCallback(Handler.java:808)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5542)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:657)
at dalvik.system.NativeStart.main(Native Method)

To successfuly find any widget in Navigation Drawer's header, you need to obtain header view first. This can be achieved by using getHeaderView() method:
View header = ((NavigationView)findViewById(R.id.navigation_view)).getHeaderView(0);
Then, having header pointing to the right ViewGroup with our widgets in it, you can use findViewById() as usual:
TextView tv = header.findViewById(R.id.songNameNavhead);
tv.setText(currentSong.getName());
Or in more compact manner:
((TextView)header.findViewById(R.id.songNameNavhead))
.setText(currentSong.getName());

private void prepareLayout() {
Log.d(LOG_TAG, "prepareLayout: Running");
((TextView) findViewById(R.id.songNameNavhead)).setText(currentSong.getName());
((TextView) findViewById(R.id.artistNavhead)).setText(currentSong.getArtist());
}
These need to use the navigationDrawer's view and then it's header, not your activity's view, so it should be
View header = navigationView.getHeaderView(0)
((TextView) navigationViewHeader.findViewById(R.id.songNameNavhead)).setText(currentSong.getName());
((TextView) navigationViewHeader.findViewById(R.id.artistNavhead)).setText(currentSong.getArtist());