ActivityGroup with custom ListView
<p>In my app, it has 4 tabs on the bottom, and each tab is connect to a ActivityGroup:</p>

<pre><code>tabHost.addTab(tabHost
.newTabSpec("Group1")
.setIndicator("group1")
.setContent(new Intent(this, Group1.class)));
</code></pre>

<p>group1 just like a interface that control the behavior of sub Activity</p>

<pre><code>this.history = new ArrayList&lt;View&gt;();
    group1 = this;

    /** a frame for its child **/
    View view = getLocalActivityManager().startActivity(
            "Group1_Layer1",
            new Intent(Group1.this, costumeList.class)
                    .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK))
            .getDecorView();
    replaceView(view);
</code></pre>

<p>and goup1 has a custom ListView:</p>

<pre><code>    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.xml, null);

            ImageView image = (ImageView) v.findViewById(R.id.cell);
                            .
                            .
        }
        return v;
    }
}
</code></pre>

<p>but it crashed, and the logCat shows:</p>

<p><code>Unable to start activity,  java.lang.NullPointerException</code></p>

<p>the crash just happened in custom ListViews,</p>

<p>other activities don't have this problem,</p>

<p>what's wrong with it? </p>
