Question

the following program force quit and crashes, I don’t understand why,

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */

    TextView tv = (TextView) findViewById(R.id.text);
    Button btn1 = (Button) findViewById(R.id.button1);

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    public void clicked(View v) {

        tv.setText(btn1.getText());
    }
}

but after moving the

TextView tv = (TextView) findViewById(R.id.text);
Button btn1 = (Button) findViewById(R.id.button1);

inside the clicked function it works, why is that?

thanks for any help..

Answer 1

Use the following code and it would start working.

You are using findViewById() before using setContentView() in the onCreate(), which would return null.

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
/** Called when the activity is first created. */

private TextView tv;
private Button btn1;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    tv = (TextView) findViewById(R.id.text);
    btn1 = (Button) findViewById(R.id.button1);
}

public void clicked(View v) {

    tv.setText(btn1.getText());
}
}