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Android Studio My Button on the second Activity doesn't Work

I think it a very easy Question. I am new to Android Studio and I could not find an answer.
I have an activity that switches per Button to another activity. However, on my second activity, my simple Button just to change the Textview which doesn't work.
Layout
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".StartActivity">
<TextView
android:id="#+id/twText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="127dp"
android:layout_marginLeft="127dp"
android:layout_marginTop="88dp"
android:layout_marginEnd="127dp"
android:layout_marginRight="127dp"
android:layout_marginBottom="624dp"
android:text="Ihr Passwort war Richtig!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/btnChecke"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="134dp"
android:layout_marginLeft="134dp"
android:layout_marginTop="32dp"
android:layout_marginEnd="189dp"
android:layout_marginRight="189dp"
android:layout_marginBottom="371dp"
android:text="Check"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
/>
</androidx.constraintlayout.widget.ConstraintLayout>
onCreate method in my second activity
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start);
tw = findViewById(R.id.twText);
btnCheck = findViewById(R.id.btnChecke);
btnCheck.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
tw.setText("work");
}
});
}
And this is how I am starting the second activity (onCreate method from my first activity).
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start);
tw = findViewById(R.id.twText);
Button btnCheck = findViewById(R.id.btnChecke);
btnCheck.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
setContentView("Work"R.layout.activity_main);
}
});
}
I have checked the variable names in the layout and looks like everything is fine.
Thank you in advance.

This answer is based on the problem which I found before the latest edit from the OP. Here is the version of the edit where I found the problem.
First of all, something is very wrong about the onClickListener of your button. You are setting the content view again, instead of starting your second activity. It looks like, you are just setting the content view of your StartActivity which actually does not launch the MainActivity that you are trying to start.
In order to start a new activity, you need to add the following in your button onClickListener.
btnCheck.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// setContentView(R.layout.activity_main); // This is not the way for starting another activity
Intent intent = new Intent(this, MainActivity.class);
startActivity(intent);
}
});
Once your MainActivity has started, you should be able to change the text with no problem.

Bundle bundle = getIntent().getExtras()
if(bundle.getString("changeTextView")
TextView .... = (TextView) ....setText();
Hi. If I good understand, you should use Intent with "putExtra()".
Exmple:intent.putExtras("changeTextView");
After that in your onCreate() method you can put:

How do I pass string from SecondActivity to MainActivity on Android Studio?

I have a public String stringPass in SecondActivity.java that I want to pass to MainActivity.java so that when I click a button, the string from the SecondActivity.java updates a TextView tv that is declared in MainActivity.java.
The bug I'm getting is that when I press the button, the string in the SecondActivity.java is not shown.
Instead, It goes from "Hello World!" to no text displayed.
FYI, i'm going to add strings to MainActivity.java from multiple activities, so I want it this particular way for my organization.
Thanks!
SecondActivity.java
public class SecondActivity extends AppCompatActivity{
public String stringPass;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
stringPass = "this is from SecondActivity";
}
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView tv = findViewById(R.id.tv);
Button btn = findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
tv.setText(new SecondActivity().stringPass);
}
});
}
}
activity_main.xml
<Button
android:id="#+id/btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="#+id/tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

Is there much content in the second activity? Is it an actual activity with much going on? If not replace it with a dialog box, when the ok button is clicked it can update the text box.

How to change text from another activity?

I am creating an Android app - using Android Studio.
The app launches in MainActivity.java which fetches activity_main.xml . On activity_main, the user can select one of 3 buttons. No matter which button they select, it will take them to the SAME layout - primary_layout.xml and the Java class associated with that is PrimaryClass.java .
I have a placeholder in primary_layout. I want this placeholder (id: placeholder) to change according to what button was previously selected.
Eg. If Button 1 (id: button1) is clicked, then the placeholder must say “Button 1 was clicked.”
Or let’s say Button 2 (id: button2) was clicked, then the placeholder must say “Button 2 was clicked”. And the same goes for Button 3.
I have created an intent to open PrimaryClass but I'm not too sure how to code the intent for when the button is clicked. I just don’t know how to change the text of the placeholder, depending on which button the user has clicked. I’ve tried using an ‘if statement’ but it doesn’t seem to work.
Or instead of creating another activity, should I rather create a fragment, and if I should, how would I code the fragment in this particular app?
I have attached images and code to better understand.
And here is my code of my classes and layout files:
MainActivity:
package com.msp.exampleapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
activity_main:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.msp.exampleapplication.MainActivity">
<Button
android:text="Button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true"
android:id="#+id/button1"
android:onClick="clickedButton1" />
<Button
android:text="Button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/button1"
android:layout_alignParentStart="true"
android:layout_marginTop="27dp"
android:id="#+id/button2"
android:onClick="clickedButton2" />
<Button
android:text="Button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/button2"
android:layout_alignParentStart="true"
android:layout_marginTop="32dp"
android:id="#+id/button3"
android:onClick="clickedButton3" />
</RelativeLayout>
PrimaryClass:
package com.msp.exampleapplication;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
public class PrimaryClass extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.primary_layout);
}
}
primary_layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:text="{holder}"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="35sp"
android:id="#+id/placeholder" />
</LinearLayout>

Your first Activity must look like this:
package com.msp.exampleapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
Button button1,button2,button3;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button1=(Button)findViewById(R.id.button1);
button2=(Button)findViewById(R.id.button2);
button3=(Button)findViewById(R.id.button3);
button1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent=new Intent(MainActivity.this, PrimaryClass.class);
intent.putExtra("message","Button 1 selected");
startActivity(intent);
}
});
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent=new Intent(MainActivity.this, PrimaryClass.class);
intent.putExtra("message","Button 2 selected");
startActivity(intent);
}
});
button3.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent=new Intent(MainActivity.this, PrimaryClass.class);
intent.putExtra("message","Button 3 selected");
startActivity(intent);
}
});
}
}
Code the second activity as below:
package com.msp.exampleapplication;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
public class PrimaryClass extends AppCompatActivity {
TextView placeholder;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.primary_layout);
placeholder=(TextView) findViewById(R.id.placeholder);
placeholder.setText(getIntent().getStringExtra("message"));
}
}

Here is solution of your problem. You have to use Intent to make action in another activity.
Code for MainActivity, create a intent on each button click like below
button_1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,PrimaryClass.class);
intent.putExtra("button_text", "Button 1 Clicked");
startActivity(intent);
}
});
Same for button 2 and 3
button_2.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,PrimaryClass.class);
intent.putExtra("button_text", "Button 2 Clicked");
startActivity(intent);
}
});
button_3.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this,PrimaryClass.class);
intent.putExtra("button_text", "Button 3 Clicked");
startActivity(intent);
}
});
Now in PrimaryClass use this code inside onCreate Method
String btn_text;
Bundle bundle = getIntent().getExtras();
if (bundle != null) {
btn_text = bundle.getString("button_text");
}
Now set text on lable
textView.setText(btn_text);
Hope you understand this, if not let me know, I'll help you.

How i can compare the value of an id with java

I have a simple xml with a question and two buttons. When one of buttons is pushed i will compare if the id of the pushed button is equal to "Blanco" or "Negro".
The XML code:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:id="#+id/textView1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/pregunta" />
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/Blanco"
android:onClick="respuesta"/>
<Button
android:id="#+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/Negro"
android:onClick="respuesta"/>
</LinearLayout>
</LinearLayout>
This is de java code:
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void respuesta(){
//The doubt.
//Here the if/else to compare ID with the button text
}
}

Don't do it like that. Create an onClickListener for each Button, so you know exactly which one is being pressed. For example:
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button1 = (Button)findViewById(R.id.button1);
Button button2 = (Button)findViewById(R.id.button2);
button1.setOnClickListener(new View.OnClickListener{
public void onClick(View v) {
// call code here, knowing that button1 was pressed
}
});
button2.setOnClickListener(new View.OnClickListener{
public void onClick(View v) {
// call code here, knowing that button2 was pressed
}
});
}
}

implement onClickListener into your Activity.
public class MainActivity extends ActionBarActivity implements OnClickListener
Declare the Button variables inside your class
Button btblanco, btnegro;
Implement the clickListener event on onCreate
btblanco = (Button) findViewById(R.id.button1);
btnegro = (Button) findViewById(R.id.button2);
btblanco.setOnClickListener(this);
btnegro.setOnClickListener(this);
And put this inside onClickListener method.
#Override
public void onClick(View v) {
switch(v.getId())
{
case R.id.button1:
Toast.makeText(getApplicationContext(), "Blanco", Toast.LENGTH_SHORT).show();
break;
case R.id.button2:
Toast.makeText(getApplicationContext(), "Negro", Toast.LENGTH_SHORT).show();
break;
}}

if you are interested in just knowing which button was clicked, then add a onclicklistener to the button objects. Google for it a bit and the samples you find will show you how to use a switch case structure to d actions based on which button was clicked.

How to do back button that go back to previous layout?

i am new in android .. I want to ask question about Link 2 layouts using buttons. I have 2 xml layout and first layout can link to 2nd layout but 2nd layout can't go back to 1st layout. Please help me.
below are my codes...
activity_main.xml
<RelativeLayout 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:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
<Button
android:id="#+id/button1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#+id/textView1"
android:layout_marginTop="120dp"
android:text="Link to page 1" />
</RelativeLayout>
page1.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" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Page 1 test"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="#+id/button2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Back to main page" />
</LinearLayout>
MainActivity.java
package com.example.linktest2;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btn1 =(Button)findViewById(R.id.button1);
btn1.setOnClickListener(new Button.OnClickListener() {
#Override
public void onClick(View v) {
Intent myIntent = new Intent();
myIntent.setAction(Intent.ACTION_VIEW);
myIntent.setData(android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI);
setContentView(R.layout.page1);
}
});
}}
page1.java
package com.example.linktest2;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class page1 extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.page1);
Button btn1 =(Button)findViewById(R.id.button2);
btn1.setOnClickListener(new Button.OnClickListener() {
#Override
public void onClick(View v) {
Intent myIntent = new Intent();
myIntent.setAction(Intent.ACTION_VIEW);
myIntent.setData(android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI);
setContentView(R.layout.activity_main);
}
});
}}

You're doing it wrong.
To go from MainActivity to page1 (by convention it should be Page1), you should start a new Activity (instead of changing the contentview of the current activity). Then to go back from Page1 to MainActivity, you can programmatically finish() the Activity, or the user can touch Back.

You can either keep your both layout in same layout file and make the show or hide the layout accordingly.
Also another way is you can create two activity which contains two separate layout and load a second layout on click of button using intent and start activity as below
To Go to other activity you can do like this :
Intent intent = new Intent(this,SecondActivity.class);
startActivity(intent);

Normally android deals with that itself.
However you can override OnBackPressed in your second activity and launch an intent that leads to your first activity
Going to other activity you can do like this :
Intent intent = new Intent(SecondActivity.this,MainActivity.class);
startActivity(intent);
For each XML you need to have another Activity.

In Main Activity :
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btn1 =(Button)findViewById(R.id.button1);
btn1.setOnClickListener(new Button.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(),page1.class);
startActivity(intent);
finish();
}
});
}
Replace this
And in your Page1 Activity replace this
public class page1 extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.page);
Button btn1 =(Button)findViewById(R.id.button2);
btn1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(),MainActivity.class);
startActivity(intent);
finish();
}
});
}
}
Hope this will help you

If you want to come back to activity A from activity B with some result,you can use like this
activity B
Intent returnIntent = new Intent();
returnIntent.putExtra("result",result);
setResult(Activity.RESULT_OK,returnIntent);
finish();
activity A
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == 1) {
if(resultCode == Activity.RESULT_OK){
String result=data.getStringExtra("result");
}
if (resultCode == Activity.RESULT_CANCELED) {
//Write your code if there's no result
}
}
}