Android App Crashes When I Try to Show HelloWorld After Button Is Clicked
<p>I have written a simple app that is supposed to show a button and when that button is clicked, it will show the text: 'Hello World' - however all it is doing is crashing at the moment.     </p>

<p>The XML is: </p>

<pre><code>&lt;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" &gt;

    &lt;TextView
        android:id="@+id/hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text=""
        tools:context=".GraphicsActivity" /&gt;

    &lt;Button xmlns:android="http://schemas.android.com/apk/res/android" 
        android:id="@+id/button_send"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Write Something..."
        android:onClick="writeMsg" /&gt;
&lt;/RelativeLayout&gt;
</code></pre>

<p>The Android source is here: </p>

<pre><code>public class GraphicsActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_graphics);
    }

    public void WriteMsg() {

        Button button = (Button) findViewById(R.id.button_send);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                TextView tv = (TextView) findViewById(R.id.hello);
                tv.setText("Hello World");
                setContentView(tv);
            }
        });
    }
}
</code></pre>

<p>As I say, all it does is crashes. By the way, I am running this in an emulator.</p>
