android why setbackgroundresource can't show the background picture
<p>i use setbackgroundresource to set the background of LinearLayout, but it cant show in the activity.</p>

<pre><code>public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);       
        sp = getSharedPreferences("config", MODE_PRIVATE);
        bgpic = sp.getInt("bgpic", 3);
        ll_main = (LinearLayout) findViewById(R.id.ll_main);
        Log.i(TAG, "图片"+imageIds[bgpic]);
        Log.i(TAG, "图片"+R.drawable.bg2);
        ll_main.setBackgroundResource(imageIds[bgpic]);
        ll_main.setBackgroundDrawable(new BitmapDrawable());
</code></pre>

<p>above is part of the code.</p>
