我想调用外部图片并在列表视图中显示它。 我的代码工作一秒钟，崩溃，给出空指针错误。代码逻辑是这样的 1.我已调用First async任务从外部获取Json对象。 然后创建自定义适配器以在自定义布局中设置该对象。 2.second异步任务获取一个对象（包含图像的url）并返回Bitmap图像。
你能说出我做错了什么吗？
Eroor：尝试调用虚方法＆＃39; void android.widget.ImageView.setImageBitmap（android.graphics.Bitmap）＆＃39;在null对象referenc
My Fragment class
public class NewsFragment extends Fragment{
private ProgressDialog pDialog;// Progress Dialog
String my_url;
ListView newsList;
ArrayList<HashMap<String, String>> postList; //Declare Array
private static String url = "http://wangeltmg.com/GKN_ADMIN/GET_POSTS/get_news.php";
GetNews.CustomAdapter CA;
View ImageView;
// JSON Node names
private static final String TAG_ID = "id";
private static final String POST_ALLPOSTS = "posts";
private static final String POST_ID = "ID";
private static final String POST_TITLE = "post_title";
private static final String POST_CONTENT = "post_content";
private static final String GUID = "guid";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.news, container, false);
newsList = (ListView) view.findViewById(R.id.newsListView);
TextView topic = (TextView) view.findViewById(R.id.topic);
postList = new ArrayList<HashMap<String, String>>();
//Get arguments
Bundle args = getArguments();
String mytopic = args.getString("Topic");
//Set topic
topic.setText(mytopic.toUpperCase());
//Execute getContacts
new GetNews().execute();
newsList.setOnItemClickListener(new newsListClick());
return view;
}
public class newsListClick implements ListView.OnItemClickListener{
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.d("News List","Clicked " + id);
android.support.v4.app.FragmentManager fragmentManager = getFragmentManager();
android.support.v4.app.FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
SinglePost singleFrag = new SinglePost();
fragmentTransaction.replace(R.id.content_frame, singleFrag);
fragmentTransaction.commit();
}
}
//Async Task
private class GetNews extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
ServiceHandler sh = new ServiceHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);
Log.d("Strings","Checking Json");
Log.d("Response: ", "> " + jsonStr);
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// contacts JSONArray
JSONArray posts = null;
// Getting JSON Array node
posts = jsonObj.getJSONArray(POST_ALLPOSTS);
// looping through All Contacts
for (int i = 0; i < posts.length(); i++) {
JSONObject c = posts.getJSONObject(i);
Log.d("Post->",posts.getJSONObject(i).toString());
String id = c.getString(POST_ID);
Log.d("Post->ID",id);
String post_title = c.getString(POST_TITLE);
String post_content = c.getString(POST_CONTENT);
String guid = c.getString(GUID);
Log.d("GUID->",guid);
//String gender = c.getString(TAG_GENDER);
// tmp hashmap for single post
HashMap<String, String> post = new HashMap<String, String>();
int count = 1;
// adding each child node to HashMap key => value
post.put(POST_ID, id);
post.put(POST_TITLE, post_title);
post.put(POST_CONTENT, post_content);
post.put(GUID, guid);
post.put("ListCount",String.valueOf(i));
// adding contact to contact list
postList.add(post);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
//get the bitmap url
return null;
}
@Override
public void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
// Updating parsed JSON data into ListView
/*
ListAdapter adapter = new SimpleAdapter(getActivity(), postList, R.layout.list_item,
new String[] { POST_TITLE,POST_CONTENT, GUID },
new int[] {R.id.email, R.id.mobile, R.id.guid });
*/
CA = new CustomAdapter( getActivity(), R.layout.list_item, postList);
newsList.setAdapter(CA);
}
public class CustomAdapter extends ArrayAdapter<HashMap<String, String>>{
private final ArrayList<HashMap<String, String>> objects;
public CustomAdapter(Context context, int resource, ArrayList<HashMap<String, String>> objects) {
//something is wrong with super
super(context, resource, objects);
this.objects = objects;
}
public View getView(int position, View convertView, ViewGroup Parent){
//convertView = new ImageView();
if(convertView == null){
LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.list_item,null);
}
TextView thisview = (TextView) convertView.findViewById(R.id.email);
int getListPos = newsList.getFirstVisiblePosition();
//i set the count starting 0 and saved in the hashmap array
//to compare the first result with the first position of listview
int count = Integer.parseInt(objects.get(position).get("ListCount"));
if(getListPos == count) {
LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.list_item_header,null);
TextView HeaderText = (TextView) convertView.findViewById(R.id.headertext);
TextView HeaderContent = (TextView) convertView.findViewById(R.id.headercontent);
HeaderText.setText(objects.get(position).get(POST_TITLE).toUpperCase());
HeaderContent.setText(objects.get(position).get(POST_CONTENT));
}else{
thisview.setText("Normal line");
}
my_url = objects.get(position).get(GUID);
new DownloadImageTask((ImageView) convertView.findViewById(R.id.img)).execute(my_url);
return convertView;
}
}//
}// end async task
private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
ImageView bmImage;
public DownloadImageTask(ImageView bmImage) {
this.bmImage = bmImage;
}
protected Bitmap doInBackground(String... urls) {
String urldisplay = urls[0];
Bitmap mIcon11 = null;
try {
InputStream in = new java.net.URL(urldisplay).openStream();
mIcon11 = BitmapFactory.decodeStream(in);
} catch (Exception e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return mIcon11;
}
protected void onPostExecute(Bitmap result) {
bmImage.setImageBitmap(result);
}
}//
}
自定义布局：
?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#444444"
android:padding="10dp">
<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/img"/>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Large Text"
android:id="@+id/headertext"
android:layout_gravity="center_horizontal"
android:textColor="#FFFFFF"
android:textStyle="bold"
android:textSize="20dp"
android:fontFamily="http://fonts.googleapis.com/css?family=Roboto:700"/>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="New Text"
android:id="@+id/headercontent"
android:layout_gravity="center_horizontal"
android:textColor="#ffffff"
android:maxLines="2"/>
</LinearLayout>
答案 0 :(得分：1)
我可以假设以下问题：您有两种不同的自定义布局：
而且，根据你的代码，你要求他们两个：
new DownloadImageTask((ImageView) convertView.findViewById(R.id.img)).execute(my_url);
如果ImageView R.id.img 不在这两种布局中，您的应用就会崩溃。如果我是对的，您只需修复if / else并仅在需要时调用DownloadImageTask。
答案 1 :(得分：0)
Eroor：尝试调用虚方法＆＃39; void android.widget.ImageView.setImageBitmap（android.graphics.Bitmap）＆＃39;在null对象引用上清楚地表明您在构造函数中传递的ImageView参数为NULL。
您正在运行时初始化此图形单元。为什么不在开头初始化它，如
Variable_name = (ImageView) convertView.findViewById(R.id.img)
并传递您当前正在使用它的创建对象。这可能会解决您的错误。
答案 2 :(得分：0)
条件中的一些调整 - 并且有效。这是我想要设定的观点的冲突。
if(getListPos == count) {
LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.list_item_header,null);
TextView HeaderText = (TextView) convertView.findViewById(R.id.headertext);
TextView HeaderContent = (TextView) convertView.findViewById(R.id.headercontent);
HeaderText.setText(objects.get(position).get(POST_TITLE).toUpperCase());
HeaderContent.setText(objects.get(position).get(POST_CONTENT));
new DownloadImageTask((ImageView) convertView.findViewById(R.id.img)).execute(my_url);
}