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I want to do INVISIBLE on SubActivity with the button on MainActivity

SubActivity cannot INVISIBLE the button in MainActivity I tried to use intent, but I'm not sure.
it SubActivity java code
try to INSIBLE the resetB button in Sub Activity
public class SubActivity extends Activity {
Button resetH, resetH2;
Button resetB, miC;
#SuppressLint("MissingInflatedId")
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sub);
ImageButton back = (ImageButton) findViewById(R.id.back);
resetH = (Button) findViewById(R.id.resetH);
resetH2 = (Button) findViewById(R.id.resetH2);
resetB = findViewById(R.id.resetB);
resetH.setOnClickListener(new Button.OnClickListener() {
#Override
public void onClick(View view) {
resetB.setVisibility(View.VISIBLE);
}
});
resetH.setOnClickListener(new Button.OnClickListener() {
#Override
public void onClick(View view) {
resetB.setVisibility(View.INVISIBLE);
}
});
back.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), MainActivity.class);
startActivity(intent);
}
});
I used intent, but I can't move the button

Passing EditText integer to TextView via Intent app crashes after clicking (button) three

I am trying just to pass the int user input to the next class and print it, see that it works before continuing on using it or something else.
Home.java
start and exit button
public class Home extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button one = (Button) findViewById(R.id.b1);
one.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
goToSecondActivity();
}
});
Button two = (Button) findViewById(R.id.b2);
two.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
finish();
}
});
}
private void goToSecondActivity() {
Intent i = new Intent(this, SelectNumberOfPlayers.class);
startActivity(i);
}
}
SelectNumberOfPlayers.java
Taking only the numbers from the input and passing it to StartGame.class
public class SelectNumberOfPlayers extends AppCompatActivity {
EditText numberOfPlayers;
Button three;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.enter_number_of_players);
three = (Button) findViewById(R.id.button3);
three.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
String txt = numberOfPlayers.getText().toString();
Intent i = new Intent(getApplicationContext(), StartGame.class);
i.putExtra("players", txt);
startActivity(i);
}
});
}
}
StartGame.java
Receiving Int and printing to TextView
public class StartGame extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.start_game);
Intent i = getIntent();
TextView numOfPlayersVal = (TextView) findViewById(R.id.txt2);
numOfPlayersVal.setText(i.getStringExtra("Player number"));
}
}
Where is the error happening? I've set the input keyboard to take only numbers

1. you forgot to initialize youe editext first initialize it in your SelectNumberOfPlayers Activity
numberOfPlayers = (EditText) findViewById(R.id.numberOfPlayers);
2.
the key must be same to pass and receive data with intent
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.start_game);
Intent i = getIntent();
TextView numOfPlayersVal = (TextView) findViewById(R.id.txt2);
numOfPlayersVal.setText(i.getStringExtra("players"));
}

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);
}
}

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

Adding second onClick method in Android Studio?

I've just started to learn Java and I've been stumped on adding the code for a second button in an activity. I apologize for my (possible dumb question) and any wrong terminology.
Here is the MainActivity Java code:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btnGo = (Button) findViewById(R.id.btnGo);
btnGo.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, GoActivity.class));
}
});
}
}
How can I add to this code for btnEscape to go to EscapeActivity?

You just have to do exacly the same thing you do with btnGo - this is find your button by id, and then set clickListener to it. It could looks like that:
Button btnEscape = (Button) findViewById(R.id.btnEscape);
btnEscape.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, EscapeActivity.class));
}
});

The optimised way to do that is implement your class with View.OnClickListener and override the method onClick and inside it use switch cases to switch between views and apply on clicks like this:
public class SampleActivity extends AppCompatActivity implements View.OnClickListener{
Button btnGo,btnEscape;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnGo = (Button) findViewById(R.id.btnGo);
btnEscape= (Button) findViewById(R.id.btnEscape);
btnGo.setOnClickListener(this);
btnEscape.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch (v.getId()){
case R.id.btnGo:
startActivity(new Intent(MainActivity.this, GoActivity.class));
break;
case R.id.btnEscape:
startActivity(new Intent(MainActivity.this, EscapeActivity.class));
break;
default:
break;
}
}
}

In code, what the two comments by Shiram and Nik above are saying is to add the block below that begins Button btnEscape... after Button btnGo.setOnclick's block.
#Override
protected void onCreate(Bundle savedInstanceState) {
...
Button btnGo = (Button) findViewById(R.id.btnGo);
...
Button btnEscape = (Button) findViewById(R.id.<<name of button in xml>>);
btnEscape.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
... whatever ... }
});
}
In short, the following is a really good pattern to have at your fingertips:
Button btn___ = (Button) findViewById(R.id.<<name of button in xml>>);
btn___.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
... whatever ... }
});