java - Create instance of new class in Android

Question

I am new to Android programming but have a little bit of experience with Java. However, I am creating an Android application and when a user clicks a button I want a different class to instantiated... This is my MainActivity.java

private void setButtonClickListener() {
    Button budgetPeriodButton = (Button)findViewById(R.id.budgetPeriodButton);
    Button incomingsButton = (Button)findViewById(R.id.incomingsButton);
    Button outgoingsButton = (Button)findViewById(R.id.outgoingsButton);
    Button resultsButton = (Button)findViewById(R.id.resultsButton);
    budgetPeriodButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            BudgetPeriod bp = new BudgetPeriod();
            bp.changeUI();
          }

And this is the BudgetPeriod class

import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.widget.ImageView;

public class BudgetPeriod extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_budget);
        super.onCreate(savedInstanceState);
        changeUI();
    }

    public void changeUI() {
        ImageView imageView = (ImageView) findViewById(R.id.budget_icon);
        Drawable newBudgetImage;
        newBudgetImage = getResources().getDrawable(R.drawable.budget_period);
        imageView.setImageDrawable(newBudgetImage);
    }
}

If the user clicks on the button, then an error message on the emulator says "Unfortunatley, this app has had to close"

Any ideas on what I am doing wrong? Thanks

Answer 1

Start the activity like this.

budgetPeriodButton.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
       Intent intent = new Intent(v.getContext(), BudgetPeriod.class);
       startActivity(intent);
    }
});

and make sure you declared the activity in AndroidManifest.xml

<activity name=".BudgetPeriod" android:name="Budget" />