关于listView不同数据类型的加载

public class TextMessage {
private String text;

public TextMessage(String content) {
this.text = content;
}

public String getText() {
return text;
}
}

public class ImageMessage {
private int imageResId;

public ImageMessage(int imageResId) {
this.imageResId = imageResId;
}

public int getImageResId() {
return imageResId;
}
}

private interface ViewType
{
int TEXT = 0;
int IMAGE = 1;
}

@Override
public int getItemViewType(int position) {
if (getItem(position) instanceof TextMessage) {
return ViewType.TEXT;
} else {
return ViewType.IMAGE;
}
}

@Override
public int getViewTypeCount() {
return ViewTypeCount;
}

    @Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
if (getItemViewType(position) == ViewType.TEXT) {
if (convertView == null) {
convertView = layoutInflater.inflate(R.layout.text_message_item, parent, false);
}
TextView textView = (TextView) convertView.findViewById(R.id.message_content);

TextMessage textMessage = (TextMessage) messageList.get(position);
textView.setText(textMessage.getText());
} else {
if (convertView == null) {
convertView = layoutInflater.inflate(R.layout.image_message_item, parent, false);
}
ImageView imageView = (ImageView) convertView.findViewById(R.id.message_image);

ImageMessage imageMessage = (ImageMessage) messageList.get(position);
imageView.setImageResource(imageMessage.getImageResId());
}

return convertView;
}

        MessageAdapter adapter = new MessageAdapter(messages);
listView.setAdapter(adapter);