Starting a new activity android - android-activity

Question

I am trying to learn the principles of starting a new activity in android. I am using "Android studio". I have created a MainActivity class which contains a text which tells the user to push the button, and the button. When the button is pushed the new activity is supposed to start(aktivitet2Klasse). This activity contains two textviews and a button. When the first button is pressed, the tetview should display "works fine!". When the second button is pushed it is supposed to display "Finished!". The point with the app is just to start one activity from another. However after pushing the button on the first screen (first activity) the app crashes. I have studies a lot of the same issues on these sides, but I cannot figure what is wrong.
Here is the code:
The main activity:
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
private TextView instruction;
private Button startButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
instruction = (TextView) findViewById(R.id.InstruksjonsView);
startButton = (Button) findViewById(R.id.btn1);
startButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
Intent intent = new Intent(MainActivity.this,aktivitet2Klasse.class);
startActivity(intent);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
The next activity:
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class aktivitet2Klasse extends AppCompatActivity {
private Button button2;
private TextView text;
private Button button3;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
button2 = (Button) findViewById(R.id.btn2);
button3 = (Button) findViewById(R.id.btn3);
text = (TextView) findViewById(R.id.textView1);
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
text.setText("Works fine!");
}
});//End button2Listener
button3.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
text.setText("Finished!");
}
});//End button3Listener
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

Answer 1

you forgot to set the content view in the second activity
public class aktivitet2Klasse extends AppCompatActivity {
private Button button2;
private TextView text;
private Button button3;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//YOU NEED TO SET THE CONTENTVIEW
// like setContentView(R.layout.activity_secondary);
Intent intent = getIntent();
button2 = (Button) findViewById(R.id.btn2);
button3 = (Button) findViewById(R.id.btn3);
text = (TextView) findViewById(R.id.textView1);
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
text.setText("Works fine!");
}
});//End button2Listener
button3.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
text.setText("Finished!");
}
});//End button3Listener
}