I'm an Android beginner and I'building a test app to know what I can do and what I can't, and I'm trying to solve this Runtime error and don't know what to do.
Can anyone help me please? I post my code and the error
MainActvity.java:
package com.example.android.myapplication;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
EditText uname;
{
uname = (EditText) findViewById(R.id.username);
}
EditText pword;
{
pword = (EditText) findViewById(R.id.password);
}
Button btn;
{
btn = (Button) findViewById(R.id.button);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
OnClickButtonListener();
}
public void OnClickButtonListener() {
btn.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent("com.example.android.myapplication.Activity2");
startActivity(intent);
}
}
);
}
}
Log:
05-01 14:32:21.725 32378-32378/com.example.android.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.myapplication, PID: 32378
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.myapplication/com.example.android.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2555)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2773)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1434)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5930)
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:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2172)
at com.example.android.myapplication.MainActivity.<init>(MainActivity.java:12)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1690)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2545)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2773)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1434)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5930)
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:1405)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
Move all three of your statements like this one:
uname = (EditText) findViewById(R.id.username);
into onCreate(), after your setContentView() call, for two reasons:
In general, you cannot safely call methods that you inherit from Activity until after super.onCreate() has been called
You specifically cannot call findViewById() until you actually have the views, such as by calling setContentView()
Take these three line of code to oncreate method after the setcontentview method recall. That initializes your view and your NULLPOINTEREXCEPTION will not happen.
uname = (EditText) findViewById(R.id.username);
pword = (EditText) findViewById(R.id.password);
btn = (Button) findViewById(R.id.button);
Related
I am very new to Android Studio and am trying to create a log in screen which then opens an inventory screen. The problem I am having is when I click Submit to the username and password, the app completely crashes. Right now, I am just working out how to organize the layout portion of things, but need to figure out how to get this transition to work. Any help would be great!
This is the main activity code:
package com.example.cs360projectone;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
EditText username, password;
Button buttonLogIn, buttonRegister;;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
username = (EditText) findViewById(R.id.username);
password = (EditText) findViewById(R.id.newPassword);
buttonLogIn = (Button) findViewById(R.id.buttonLogIn);
buttonRegister = (Button) findViewById(R.id.buttonRegister);
buttonLogIn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if(username.getText().toString().trim().length() <1 || password.getText().toString().trim().length() <1){
username.setError("You must enter a valid username and password");
}
else {
openInventory();
}
}
});
buttonRegister.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view1) {
openRegisterScreen();
}
});
}
public void openRegisterScreen() {
Intent intent = new Intent(this, RegisterScreen.class);
startActivity(intent);
}
public void openInventory() {
Intent intent = new Intent(this, InventoryScreen.class);
startActivity(intent);
}
}
This is the inventory screen code:
package com.example.cs360projectone;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class InventoryScreen extends AppCompatActivity {
Button buttonSMS, buttonSignOut;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_inventory_screen);
buttonSMS.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view1) {
openSMSPermission();
}
});
}
public void openSMSPermission() {
Intent intent = new Intent(this, SMSPermissionScreen.class);
startActivity(intent);
}
}
This is the error from logcat when the button is pressed:
2022-08-03 16:54:09.037 8043-8043/com.example.cs360projectone E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.cs360projectone, PID: 8043
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cs360projectone/com.example.cs360projectone.InventoryScreen}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.cs360projectone.InventoryScreen.onCreate(InventoryScreen.java:18)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2022-08-03 16:54:09.062 8043-8043/com.example.cs360projectone I/Process: Sending signal. PID: 8043 SIG: 9
You need to get the SMS button in the InventoryScreen onCreate method the same way you did with the other buttons in MainActivity.
This means doing a
buttonSMS = (Button) findViewById(R.id.buttonSMS);
before setting up an onClickListener.
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed last year.
I'm studying Android java, and I have this error and can't run it.
Could you help me fixing this error? What is the problem?
Is it related to the error that I can't make a onClickListener() lambda expression? It gives me error and I can't import. So I tried making new View.OnclickListener() and its color is grey.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 9974
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3635)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7839)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.myapplication.MainActivity.onCreate(MainActivity.java:31)
at android.app.Activity.performCreate(Activity.java:8051)
at android.app.Activity.performCreate(Activity.java:8031)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1329)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3608)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7839)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
I/Process: Sending signal. PID: 9974 SIG: 9
And this is my mainActivity.
package com.example.myapplication;
import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
RadioGroup radioGroup;
TextView txtViewResults;
EditText editTextInputWt;
Button btnConvertWt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayShowHomeEnabled(true);
actionBar.setDisplayUseLogoEnabled(true);
actionBar.setLogo(R.mipmap.ic_launcher_weight_round);
actionBar.setTitle(R.string.txtTitle);
btnConvertWt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (radioGroup.getCheckedRadioButtonId() == -1){
Toast.makeText(MainActivity.this, "Please select conversion type", Toast.LENGTH_SHORT).show();
} else if (editTextInputWt.getText().toString().isEmpty()){
Toast.makeText(MainActivity.this, "Please select baggage weight", Toast.LENGTH_SHORT).show();
} else {
double inputWt, outputWt;
try{
inputWt = Double.parseDouble(editTextInputWt.getText().toString());
if (inputWt<0){
Toast.makeText(MainActivity.this, "Baggage weight can't be negative.", Toast.LENGTH_SHORT).show();
} else if (radioGroup.getCheckedRadioButtonId() == R.id.radBtnKgsToLbs){
if (inputWt > 500){
Toast.makeText(MainActivity.this, "Input bg wt can't be greater than 500Kilos", Toast.LENGTH_SHORT).show();
} else {
outputWt = inputWt*2.2;
txtViewResults.setText(String.format("Converted wt: %.2f Lbs", outputWt));
}
} else if (radioGroup.getCheckedRadioButtonId() == R.id.radBtnLbsToKgs){
if (inputWt > 1000){
Toast.makeText(MainActivity.this, "Input bg wt can't be greater than 1000 pounds", Toast.LENGTH_SHORT).show();
} else {
outputWt = inputWt/2.2;
txtViewResults.setText(String.format("Converted wt: %.2f Kgs", outputWt));
}
}
} catch (Exception ex){
ex.printStackTrace();
}
}
}
});
}
}
This is due to you haven't initialised your views and as of this stage they are null and you can't invoke method on null object in java which you can see in your error.
so for this you have to initalise your variable you can do like following
findViewById()
View Binding
Data Binding
Creating view programmatically
as you have used layout file you can do findViewById() as following
public class MainActivity extends AppCompatActivity {
RadioGroup radioGroup;
TextView txtViewResults;
EditText editTextInputWt;
Button btnConvertWt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
....
radioGroup = findViewById(R.id.my_radio_group);
btnConvertWt = findViewById(R.id.my_button); // the id's are same as defined in your layout file
....
btnConvertWt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
....
}
});
}
}
I am writing an app for my company but I cannot see my work since my emulator is not running.
Here is my code below. There are no errors. I am running this in android studio.
It runs on some apps but I tried inputting my code then it does not work.
Please Help
package com.example.tankoverfill;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
Button calc;
TextView tv_heightfills = findViewById(R.id.tv_heightfills);
TextView tv_timefills = findViewById(R.id.tv_timefills);
EditText flow, areas, heights, densities, heightones, cvs;
int x1,y1,w1,a1, x2,y2,w2,a2,g;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
flow = findViewById(R.id.flow);
areas = findViewById(R.id.areas);
heights = findViewById(R.id.heights);
densities = findViewById(R.id.densities);
heightones = findViewById(R.id.heightones);
cvs = findViewById(R.id.cvs);
calc = findViewById(R.id.calc);
calc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
x1 = Integer.parseInt(flow.getText().toString());
y1 = Integer.parseInt(cvs.getText().toString());
w1 = Integer.parseInt(densities.getText().toString());
g = (int) 9.8;
a1 = (x1 / (y1*w1*g));
tv_heightfills.setText(a1);
}
});
calc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
x2 = Integer.parseInt(areas.getText().toString());
y2 = Integer.parseInt(cvs.getText().toString());
w2 = Integer.parseInt(densities.getText().toString());
g = (int) 9.8;
a2 = (x1 / (y1*w1*g));
tv_timefills.setText(a2);
}
});
}
}
D/AndroidRuntime: Shutting down VM E/AndroidRuntime: FATAL EXCEPTION:
main
Process: com.example.tankoverfill, PID: 10137
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.tankoverfill/com.example.tankoverfill.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method
'android.view.Window$Callback android.view.Window.getCallback()' on a
null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback
android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImpl.(AppCompatDelegateImpl.java:249)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
at com.example.tankoverfill.MainActivity.(MainActivity.java:15)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
at android.support.v4.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:43)
at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
I/Process: Sending signal. PID: 10137 SIG: 9 Application terminated.
Hello two of the errors you have in your code are:
first error that you must link the two textview to xml inside onCreate() method
error
TextView tv_heightfills = findViewById(R.id.tv_heightfills);
TextView tv_timefills = findViewById(R.id.tv_timefills);
correct
TextView tv_heightfills;
TextView tv_timefills;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv_heightfills = findViewById(R.id.tv_heightfills);
tv_timefills = findViewById(R.id.tv_timefills);
....
}
Second error is setting int value to the textview setText() method
so it should be:
tv_heightfills.setText(String.valueOf(a1));
same for
tv_timefills.setText(String.valueOf(a2));
First, I'm new to android SDK but I have a decent amount of experience in java. I'm attempting a tutorial on the SDK to get into it. I completed writing everything required but when I go to run it, the app crashes and I get this fatal error:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
Ok, sure. Clearly, there is an issue with View.OnClickListener. Spelling, check. Capitalization, check. Parenthesis, check. Brackets, check. Semicolons, check. Next I checked the documentation for View.OnClickListener. I see its only method is onClick(View v). Ok well everything is fine there. The IDE isn't giving me any other errors. So at this point, I figure I need outside help. For referance, this is the button id:
android:id="#+id/button"
This is MainActivity.java
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.content.Intent;
import android.view.View;
public class MainActivity extends AppCompatActivity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v){
goToSecondActivity();
}
});
}
private void goToSecondActivity() {
Intent intent = new Intent(this, SecondActivity.class);
startActivity(intent);
}
}
And here is the logcat
08-20 16:00:01.171 2565-2565/com.example.joe.helloworld E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.joe.helloworld, PID: 2565
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.joe.helloworld/com.example.joe.helloworld.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.joe.helloworld.MainActivity.onCreate(MainActivity.java:16)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
You've forgotten to call setContentView() with the layout id that contains the Button.
Since there is no content layout, calls to findViewById() return null.
setContentView(R.layout.activity_main);
Right after super.onCreate(...)
You forgot to set the layout for the user to view :
setContentView(R.layout.activity_main);
Also Instead of using :
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v){
goToSecondActivity();
}
});
}
Just use this :
button.setOnClickListener(new Button.OnClickListener()
{
#Override
public void onClick(View v){
goToSecondActivity();
}
});
}
That means inside setOnClickListener use new Button.OnClickListener instead of View.OnClickListener
I created simple application in android. I have a user profile in navigation drawer. when choose address option in that drawer Open that fragment (Example:Address fragment). In that layout i put save button. While click that save button i want validate all the fields. But, when i choose that option from the drawer, application unfortunately stopped.
My code here:
AddressFragment.java
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class AddressFragment extends Fragment {
EditText line2;
Button addrsave;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_layout_address, container, false);
addrsave = (Button) getActivity().findViewById(R.id.addrsave);
// Get a reference to the AutoCompleteTextView in the layout
AutoCompleteTextView textView = (AutoCompleteTextView) view.findViewById(R.id.city_autoCompleteTextView);
// Get the string array
String[] city = getResources().getStringArray(R.array.city);
// Create the adapter and set it to the AutoCompleteTextView
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, city);
textView.setAdapter(adapter);
addrsave.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String addr = line2.getText().toString();
if (addr.equals("")) {
Toast.makeText(getActivity().getApplicationContext(), "Field cannot be left blank.", Toast.LENGTH_SHORT).show();
}
}
});
return view;
}
}
My logcat:
07-22 12:47:46.235 6355-6355/com.h2o E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.h2o, PID: 6355
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.h2o/com.h2o.AccountActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.h2o.AddressFragment.onCreateView(AddressFragment.java:38)
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.FragmentActivity.onStart(FragmentActivity.java:551)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1220)
at android.app.Activity.performStart(Activity.java:5953)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
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:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Please anyone help!!
Thanks in advance!!!
Change this:
addrsave = (Button) getActivity().findViewById(R.id.addrsave);
to this:
addrsave = (Button) view.findViewById(R.id.addrsave);
Problem is that you are doing findViewById() on getActivity() which gives you a null. And then setting an onClickListener on it will throw NullPointerException.
Hope it helps! :)
Change this line
addrsave = (Button) getActivity().findViewById(R.id.addrsave);
to
addrsave = (Button) view.findViewById(R.id.addrsave);
Your R.layout.fragment_layout_address is assigned to view so you have to use view variable to get the button from layout. Secondly, Also initialize line2 which will throw an exception of NPE(Null Pointer) once you resolve the first issue
I cant see where you have initialized line2 ?
So line2 is null which might cause the exception
String addr = line2.getText().toString();
I think you have added button in fragment and you are trying to retrive it from activity. So change retrieving the view from getActivity() to view like below
addrsave = (Button) getActivity().findViewById(R.id.addrsave);
Replace the above with the following line
addrsave = (Button) view.findViewById(R.id.addrsave);
And You missed the line2 view initialization in line number 38