Android: Layout.addView() doesn't work

When I try to run the following code I get an error. The emulator gives me this error message and then the app force closes: The application has stopped unexpectedly. What is wrong?

import edu.chl.dat255.bluebanana.R;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Linear开发者_运维技巧Layout;
import android.widget.TextView;

public class ProMan extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        LinearLayout layout = (LinearLayout) findViewById(R.layout.main);

        TextView t = new TextView(getApplicationContext());
        t.setText("Hello world");
        layout.addView(t);
    }
}

---

  LinearLayout layout = (LinearLayout) findViewById(R.id.mainLayout);

In your xml file main xml layout android:id="@+id/mainLayout" 

---

You should set id for your root LinearLayout in main.xml like

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/mainLayout">

and then reference it as

LinearLayout layout = (LinearLayout) findViewById(R.id.mainLayout);

instead of findViewById(R.layout.main);

---

You should provide layout information on `TextView t . layout width and layout height should be provided. See code below.

LinearLayout.LayoutParams params = 
    new LinearLayout.LayoutParams( 
       ViewGroup.LayoutParams.WRAP_CONTENT, 
       ViewGroup.LayoutParams.WRAP_CONTENT, 0.0F);
t.setLayoutParams(tvParams);

layout.addView(t);