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On clicking button the app goes back to homepage

So I am new and working on an app, so I have created homepage of it and then when we click on anyone of it it opens a new activity in which when clicking the button to get the answer doesnt work and it goes back to the homepage. Please help me solve this!
This is my code of main activity
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
CardView Currency = (CardView) findViewById(R.id.Currency);
CardView Area = (CardView) findViewById(R.id.Area);
CardView Length = (CardView) findViewById(R.id.Length);
CardView Temperature = (CardView) findViewById(R.id.Temperature);
CardView Time = (CardView) findViewById(R.id.Time);
CardView Weight = (CardView) findViewById(R.id.Weight);
Currency.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Currency.class);
startActivity(intent);
}
});
Weight.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Weight.class);
startActivity(intent);
}
});
Time.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Time.class);
startActivity(intent);
}
});
Length.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Length.class);
startActivity(intent);
}
});
Area.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Area.class);
startActivity(intent);
}
});
Temperature.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,Temperature.class);
startActivity(intent);
}
});
}
And this is of my new activity to open at homepage and convert the value
public class Weight extends AppCompatActivity {
private TextView textView;
private Button button;
private EditText editText;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_weight);
button = findViewById(R.id.button);
textView = findViewById(R.id.textView);
editText = findViewById(R.id.editText);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Toast.makeText(Weight.this, "Request Proceeded", Toast.LENGTH_SHORT).show();
String s = editText.getText().toString();
Integer.parseInt(s);
int kg = Integer.parseInt(s);
double pound = 2.205 * kg;
textView.setText("The corresponding value in Pound is" + pound);
}
});
}

Unable to instantiate activity?

i'm getting this error
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.bassammetwally.like/com.example.bassammetwally.like.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
when i'm trying to switch activity in another method in the
mainActivity.class
The Code i'm trying to run(not going to include libraries);
public class MainActivity extends AppCompatActivity {
final Intent i = new Intent(this, profile.class);
ImageButton ButtonOne = (ImageButton) findViewById(R.id.profile);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Intent i = new Intent(this, profile.class);
ImageButton ButtonOne = (ImageButton) findViewById(R.id.profile);
ButtonOne.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
button();
}
});
}
public void button()
{
startActivity(i);
}
}
code before that worked
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Intent i = new Intent(this, profile.class);
ImageButton ButtonOne = (ImageButton)findViewById(R.id.profile);
ButtonOne.setOnClickListener(new View.OnClickListener(){
public void onClick( View v ){
startActivity(i);
}
});
}}
Questions:
What is the meaning of the error?
why is this error showing?

Try this code:
final Intent i ;
ImageButton ButtonOne ;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
i =new Intent(MainActivity.this, profile.class);
ButtonOne = (ImageButton) findViewById(R.id.profile);
ButtonOne.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
button();
}
});
}
public void button()
{
startActivity(i);
}

public class MainActivity extends AppCompatActivity
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageButton ButtonOne = (ImageButton) findViewById(R.id.profile);
ButtonOne.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(this, profile.class);
startActivity(i);
}
});
}
}
Also Added Profile.java in manifest file

You're initiating variable i twice. When going to function button() you are using the one in public scope (above the onCreate method), not the one from onCreate. Your code should look like this:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Intent i = new Intent(this, profile.class);
ImageButton ButtonOne = (ImageButton) findViewById(R.id.profile);
ButtonOne.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
button(i);
}
});
}
public void button(Intent i)
{
startActivity(i);
}
}

Getting a crash every time i press a button"Android Studio"

I am trying to make a mobile application,but when ever i try to press the button i get a crash. The button should take me to a new activity page, i have already connect the other pages with the button in a right way. i am just wondering if this code is correct or not:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onButtonClick(View v)
{
Button a1= (Button) findViewById(R.id.button);
a1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, SecondPage.class);
startActivity(intent);
}
});
}
public void onButtonClick1(View c)
{
Button a1= (Button) findViewById(R.id.button2);
a1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this, ThirdPage.class);
startActivity(intent);
}
});
}
public void onButtonClick2(View d)
{
Button a1= (Button) findViewById(R.id.button3);
a1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this, FourthPage.class);
startActivity(intent);
}
});
}
public void onButtonClick3(View f)
{
Button a1= (Button) findViewById(R.id.button4);
a1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this, FifthPage.class);
startActivity(intent);
}
});
}
}
i just learned java from some videos in the youtube,so i am not sure if i did the activity function well or not. Thank you

There can be few reasons after it
1) Make sure you defined activity in Manifest file
2) check for android:onClick="" in xml file..
OR
Try Binding Buttons in onCreate() method.
and You can simply use this for onClick
a1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, SecondPage.class);
startActivity(intent);
}
});

Remove onClick attribute in your activity_main.xml file and copy and past this code in your MainActivity.java file
public class MainActivity extends AppCompatActivity {
Button b1,b2,b3,b4;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1= (Button) findViewById(R.id.button);
b2= (Button) findViewById(R.id.button2);
b3= (Button) findViewById(R.id.button3);
b4= (Button) findViewById(R.id.button4);
b1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, SecondPage.class);
startActivity(intent);
}
});
b2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this, ThirdPage.class);
startActivity(intent);
}
});
b3.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this, FourthPage.class);
startActivity(intent);
}
});
b4.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this, FifthPage.class);
startActivity(intent);
}
});
}
}

If you are using the onclick attribute in layout XML then you doesn't need to set the onclick listener. If you are not using onclick then you need to set click listener. In your case your case, I think use are using onclick attribute in layout XML and also trying to set the click listener in using java code. so you need to either use onclick attribute in layout XML or use setOnCliickListener() in java code

Multiple buttons in MainActivity Android studio

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
EditText textmsg;
static final int READ_BLOCK_SIZE = 100;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textmsg = (EditText) findViewById(R.id.editText1);
}
#Override
public void onClick(View v) {
Button noteBtn = (Button) findViewById(R.id.noteBtn);
Button resuBtn = (Button) findViewById(R.id.resuBtn);
Button agenBtn = (Button) findViewById(R.id.agenBtn);
noteBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Notes.class);
}
});
resuBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Results.class);
}
});
agenBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Agenda.class);
}
});
When I run the application the buttons don't work. If I set the buttons as so..
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button agenBtn = (Button) findViewById(R.id.agenBtn);
Button resuBtn= (Button) findViewById(R.id.resuBtn);
Button noteBtn = (Button) findViewById(R.id.noteBtn);
agenBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Agenda.class);
startActivity(intent);
}
}); etc...
If I use this code above, the code works fine and the buttons work correctly. But other functionality with different classes/activities won't run. Could someone please show me a solution or explain how to solve this issue.

You should place:
this.noteBtn = (Button) findViewById(R.id.noteBtn);
this.notBtn.setOnClickListener(this);
this.resuBtn = (Button) findViewById(R.id.resuBtn);
this.resuBtn.setOnClickListener(this);
this.timeBtn = (Button) findViewById(R.id.timeBtn);
this.timeBtn.setOnClickListener(this);
in onCreate() instead of onClick(). Make the buttons belong to the class, so you can reference them in onClick(). You should not be setting new onClickListeners in onClick(), but should rather have a switch statement based on the clicked view's id to determine which button was pressed.

this code
#Override
public void onClick(View v) {
Button noteBtn = (Button) findViewById(R.id.noteBtn);
Button resuBtn = (Button) findViewById(R.id.resuBtn);
Button timeBtn = (Button) findViewById(R.id.timeBtn);
...
}
is not working because it's never going to get call, since none of your buttons is implementing it, worse yet they have not even been initialized because the onClick has not and will never be called.
the correct way to do it is like:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button but1 = (Button) findViewById(R.id.but1);
Button resBtn = (Button) findViewById(R.id.resBtn);
Button noteBtn = (Button) findViewById(R.id.noteBtn);
agendaBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View viewTimeTable) {
Intent intent = new Intent(MainActivity.this, Agenda.class);
startActivity(intent);
}
}); etc...
because you are first getting a reference to your buttons and assigning them the onClickListener to each one of it.
I will suggest reading more about the Android Activity life cycle you can find it
here

Idea set onClickListener. Game crashes at the start. (Java)

My problem is in set OnClickListener I don't know why but always at the start my game crushes:
ImageButton button1 = (ImageButton) findViewById(R.id.imagePlay);
button1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
callListOfLevels();
}
});
ImageButton button2 = (ImageButton) findViewById(R.id.imageQuit);
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
finish();
}
});
}
public void callListOfLevels(){
Intent intent = new Intent(this, ListOfLevels.class);
startActivity(intent);
}