Develop Reference

Android Studio Error: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 1 year ago.
I have been trying to create this custom dialog window for my app, where it will pop up when pressed and request the user's numerical input. I have tested this custom dialog thing before and it has worked in the past successfully, however when I tried it in this case, it kept throwing out the error of "Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference" at
final EditText inputNumber = input_score.findViewById(R.id.inputNumber);
numberOfPoints = Integer.parseInt(inputNumber.getText().toString());
This error, when pressing the button to bring up the custom pop-up window, would cause the screen to blackout for a few seconds before returning to the app's main menu. What's supposed to happen is the dialog window popping up to get the user's input
private void openDialog() {
input_score = new Dialog(this);
beginButton = findViewById(R.id.beginButton);
final EditText inputNumber = input_score.findViewById(R.id.inputNumber);
numberOfPoints = Integer.parseInt(inputNumber.getText().toString());
input_score.setContentView(R.layout.input_score);
input_score.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
input_score.show();
beginButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (inputNumber.getText().toString().trim().isEmpty()) {
//change textview to error for a few seconds before returning to normal
} else {
if (Integer.parseInt(inputNumber.getText().toString()) <= 0 || Integer.parseInt(inputNumber.getText().toString()) > 900) {
startActivity(new Intent(MainMenu.this, MainGame.class));
}
}
}
});
Full Error Log:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.rockpaperscissors, PID: 4683
java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
at com.example.rockpaperscissors.MainMenu.openDialog(MainMenu.java:67)
at com.example.rockpaperscissors.MainMenu.access$000(MainMenu.java:20)
at com.example.rockpaperscissors.MainMenu$1.onClick(MainMenu.java:47)
at android.view.View.performClick(View.java:7217)
at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
at android.view.View.performClickInternal(View.java:7191)
at android.view.View.access$3500(View.java:828)
at android.view.View$PerformClick.run(View.java:27679)
at android.os.Handler.handleCallback(Handler.java:900)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:219)
at android.app.ActivityThread.main(ActivityThread.java:8347)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1055)
I'm not sure how I go about exactly fixing this, so please do point out the errors made in the code to improve and sort it out. Thank you
EDIT: As #Shay Kin showed, he used a onShowListener then put the button Listener within it, so that it would know that when this dialog would pop up, then to pop up the button function along with it. In my case, the reason the code kept breaking was not only because of mispositioning the .show but also due to the fact that I had this variable "numberOfPoints" which kept parsing an empty text field and breaking the code since no value was inside. I had not noticed this until I went through it deeply again and deleted that variable.
The things I did to fix the code was by implementing his solution, which had already incorporated the buttonListener into it, and delete the numberOfPoints variable. This resulted in the program being fixed and working successfully

Maybe because the EditText is in a different scope? Try declaring the EditText outside the function (Beside your other components). The onClick() function is a callback so maybe the EditText is being disposed of once the openDialog() finishes executing.

Before you call Dialog.show(), the view doesn't yet exist, thus your findViewById() doesn't find the desired view, returning null instead. The views would only be available after calling either show() or create().
Since you don't actually need it in advance, you can move this initialization to where you actually need it.
beginButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Initialize it here
final EditText inputNumber = input_score.findViewById(R.id.inputNumber);
if (inputNumber.getText().toString().trim().isEmpty()) {
//change textview to error for a few seconds before returning to normal
} else {
if (Integer.parseInt(inputNumber.getText().toString()) <= 0 || Integer.parseInt(inputNumber.getText().toString()) > 900) {
startActivity(new Intent(MainMenu.this, MainGame.class));
}
}
}
});
However, it's important to mention that you should avoid using the Dialog class directly, as per official documentation.

As #Gabriel said You got NullPointerException because you initialize the EditText After the dialog is shown so you can add listener and when you're Dialog is become visible here you can initialize all your view
private void openDialog() {
input_score = new Dialog(this);
input_score.setContentView(R.layout.speach_dialog);
input_score.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
input_score.setOnShowListener(new DialogInterface.OnShowListener() {
#Override
public void onShow(DialogInterface dialog) {
beginButton = findViewById(R.id.beginButton);
final EditText inputNumber = input_score.findViewById(R.id.inputNumber);
numberOfPoints = Integer.parseInt(inputNumber.getText().toString());
beginButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (inputNumber.getText().toString().trim().isEmpty()) {
//change textview to error for a few seconds before returning to normal
} else {
if (Integer.parseInt(inputNumber.getText().toString()) <= 0 || Integer.parseInt(inputNumber.getText().toString()) > 900) {
startActivity(new Intent(MainMenu.this, MainGame.class));
}
}
}
});
}
});
input_score.show();
}

Android app crashes when changing activity [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 2 years ago.
New to Android developing, using Android Studio. The first activity of my app is a simple main menu with a "Start" and a "Quit" button. When i press the "Start" button, the app should take me to the second activity named "EncounterScreen". Instead, the app crashes. enter image description here. I am trying to display the current health of the player object, of class Player. Apparently the problem is with "TextView healthText=findViewById(R.id.healthText);". This is the error: "Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference"
public class EncounterScreen extends AppCompatActivity implements View.OnClickListener {
Player player=new Player();
TextView healthText=findViewById(R.id.healthText);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_encounter_screen);
Player player=new Player();
TextView healthText=findViewById(R.id.healthText);
healthText.setText("Health "+player.getCurrentHP());
Button attackButton=findViewById(R.id.attackBtn);
Button drinkPotButton=findViewById(R.id.drinkPotBtn);
Button runButton=findViewById(R.id.runBtn);
attackButton.setOnClickListener(this);
drinkPotButton.setOnClickListener(this);
runButton.setOnClickListener(this);
}
#SuppressLint("SetTextI18n")
#Override
public void onClick(View view) {
switch (view.getId()){
case R.id.drinkPotBtn:
player.drinkPotion(player);
healthText.setText("Health "+player.getCurrentHP());
break;
}
}

Make sure the TextView id that you are trying to find has the correct id. You are using "R.id.healthText"
Does the TextView in your activity_ecounter_screen have a different id?

Player player=new Player();
TextView healthText=findViewById(R.id.healthText);
I believe the issue is with the above line. remove =findViewById(R.id.healthText).

Attempt to invoke virtual method void android.widget.ImageView.startAnimation on a null object reference [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
findViewById() returns null for Views in a Dialog
(4 answers)
Closed 4 years ago.
I want when a user clicks on "ans_three_btn_one" button than a dialog appears and in that dialogbox, I want to implement rorate animation on sunburst imageview. The only problem in this code is "sunburst.startAnimation". If I remove this line then code work properly but no animation. With this line of code my app crashing. Appreciate If you help me.
public class GamePlay extends AppCompatActivity implements View.OnClickListener {
Button ans_three_btn_one;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game_play);
ans_three_btn_one = findViewById(R.id.ans_three_first_btn);
ans_three_btn_one.setOnClickListener(this);
}
#Override
public void onClick(View v) {
Dialog first_prize_dialog = new Dialog(this,android.R.style.Theme_Black_NoTitleBar_Fullscreen);
first_prize_dialog.setContentView(R.layout.activity_first_prize);
first_prize_dialog.getWindow().setBackgroundDrawableResource(android.R.color.transparent);
first_prize_dialog.show();
ImageView sunbrust = findViewById(R.id.sunbrust_img);
//----Error area start ---
sunbrust.startAnimation(AnimationUtils.loadAnimation(v.getContext(),R.anim.rotate));
//----Error area end ---
}
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.startAnimation(android.view.animation.Animation)' on a null object reference
Application terminated.

You have missed first_prize_dialog before findViewById.
It will be
ImageView sunbrust = first_prize_dialog.findViewById(R.id.sunbrust_img);

Attempt to invoke virtual method in material dialog

I am using a library which can be found HERE to create material-design style dialog in an android app. I have made it so that the dialog opens when a FAB is clicked.
public void onClick(View v) {
final RatingBar mRatingBar = (RatingBar) findViewById(R.id.ratingBar);
final EditText input = (EditText) findViewById(R.id.editText);
new MaterialDialog.Builder(MainActivity.this)
.title(R.string.title)
.positiveText(R.string.agree)
.negativeText(R.string.disagree)
.customView(R.layout.dialog_view, true)
.callback(new MaterialDialog.ButtonCallback() {
#Override
public void onPositive(MaterialDialog dialog)
String sentReview = input.getText().toString();
float starCount = mRatingBar.getNumStars();
}
})
.show();
}
The dialog successfully opens, and everything works well until I click the positive button "send". It then says "unfortunately DemoApp has stopped".
The exception is : java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText() on a null object reference.
The line that appears to be causing it is: String sentReview = input.getText().toString();.
If I comment the section which deals with the edit text and sent Review, the same problem will appear with my rating bar.
I have seen similar questions, but none of them precisely match my problem, and none of the methods they use work when I attempt to apply them to my application.
Thanks,
Geffen Avraham

null pointer exception when adding an onclicklistener to a button outside the main view

I want to have access to objects in views from views other than the main content view in the app. How can I go about doing this?
I am trying to add an onclicklistener, but it fails every time because the program can't seem to find the button.
02-12 15:26:29.034: E/AndroidRuntime(11788): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.evolutionsystems.kiroco/com.evolutionsystems.kiroco.OverviewActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
Or am I going about this the wrong way? Should I include all the buttons in the main view and have them set to hidden and then change them dynamically as the user interacts with the program?
EDIT - This is the type of code that throws the error.
final Button receiver = (Button) findViewById(R.id.receiver);
receiver.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
aboutKirocoClicked(v);
}
});
The receiver button is part of a different view to the content view so the program can't find it and it returns null.

When you call findViewById( int ) you are asking for a view within the context of the object you called.
So if this is an activity then the object must be part of the xml resource from setContent.
You can also find resources from other inflated layouts ( menu, fragement ), but you must call the findViewById on that object inorder to find the view.
Not to complicate your life, but once you are more comfortable with Android you may want to check out a dependency injection framework like Roboguice or Dagger.

In your Activity, where you would like your button to appear, you add the following code:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//In activity_main.xml, you have a button.
setContentView(R.layout.activity_main);
//You get this button with the referencing ID
Button myBtn = (Button) findViewById(R.id.my_btn_id);
//Now, you can set your onClickListner
myBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Handle your button click
}
});
}