关于listview中getview方法中无法实例化控件

菜鸟一个，有个问题很纠结，实在是搞不明白问题在什么地方，debug的状态时holder.tv_homeline_filmname为空导致出错，数据都取到了，但控件为空无法赋值，请问什么原因public View getView(final int position, View convertView, ViewGroup parent) {

holder=new ViewHolder();  
if (convertView == null) {

convertView = mInflater.inflate(R.layout.myhomeline, null);
holder.tv_homeline_userimage = (ImageView)convertView.findViewById(R.id.tv_homeline_userimage);
holder.tv_homeline_username = (TextView)convertView.findViewById(R.id.tv_homeline_username);
holder.tv_homeline_comment = (TextView)convertView.findViewById(R.id.tv_homeline_comment);
holder.tv_homeline_filmimage=(ImageView) findViewById(R.id.tv_homeline_filmimage);
holder.tv_homeline_filmname =(TextView) findViewById(R.id.tv_homeline_filmname);
holder.tv_homeline_title=(TextView) findViewById(R.id.tv_homeline_title);
holder.tv_homeline_currenttime =(TextView) findViewById(R.id.tv_homeline_currenttime);
convertView.setTag(holder);
}else {
holder = (ViewHolder)convertView.getTag();
}

new AsyncTask<Void, Void, Bitmap>(){
@Override
protected void onPostExecute(Bitmap result) {
holder.tv_homeline_userimage.setImageBitmap(result);
super.onPostExecute(result);
} @Override
protected Bitmap doInBackground(Void... params) {
Bitmap bitmap;
try {
ImageDownloder imageDownloder = new ImageDownloder();
bitmap = imageDownloder.imageDownloder(userList.get(position).getImage());
return bitmap;
} catch (Exception e) {
e.printStackTrace();
return null;
}

}
}.execute();
new AsyncTask<Void, Void, Bitmap>(){
@Override
protected void onPostExecute(Bitmap result) {
if("".equals(result)){

holder.tv_homeline_filmimage.setImageResource(R.drawable.icon);
}else{
holder.tv_homeline_filmimage.setImageBitmap(result);
}
super.onPostExecute(result);

} @Override
protected Bitmap doInBackground(Void... params) {
Bitmap bitmap;
try {
ImageDownloder imageDownloder = new ImageDownloder();
String path=programList.get(position).getImagePath();
if("".equals("path")){
bitmap = imageDownloder.imageDownloder(path);
return bitmap;
}else{
return null;
}
} catch (Exception e) {
e.printStackTrace();
return null;
}

}
}.execute();

holder.tv_homeline_username.setText(userList.get(position).getName());
holder.tv_homeline_comment.setText(myHomeLineDiscList.get(position).getComment());
holder.tv_homeline_filmname.setText((programList.get(position)).getTitle());
holder.tv_homeline_title.setText(myHomeLineDiscList.get(position).getTopic().getTopic_name());
SimpleDateFormat sDateFormat= new  SimpleDateFormat("yyyy-MM-dd    hh:mm:ss");     
Calendar dateAndTime = Calendar.getInstance(Locale.CHINA);
holder.tv_homeline_currenttime.setText(sDateFormat.format(dateAndTime.getTimeInMillis()));
return convertView;
}
}