我正在尝试使用基本适配器创建列表视图，但它显示我的空白屏幕但有警告，这是我的适配器类
public class SuggestionListAdapter extends BaseAdapter implements View.OnClickListener {
private Activity activity;
private List suggestion;
private Post post = null;
private LayoutInflater inflater;
/*Constructor*/
public SuggestionListAdapter(Activity activity, List<Post> suggestion) {
this.activity = activity;
this.suggestion = suggestion;
inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
// LayoutInflater inflater = LayoutInflater.from(activity);
}
/*Ends Here*/
@Override
public int getCount() {
return 0;
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder;
if (convertView == null) {
convertView = inflater.inflate(R.layout.row_of_list_suggestions, parent, false);
viewHolder = new ViewHolder();
viewHolder.txtvNameSuggestion = (TextView) convertView.findViewById(R.id.txtvNameSuggestion);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
viewHolder.txtvNameSuggestion.setText("hello");
return convertView;
}
@Override
public void onClick(View v) {
}
/**
* ****** Create a holder Class to contain inflated xml file elements ********
*/
public static class ViewHolder {
public TextView txtvNameSuggestion;
public TextView txtvUsernameSuggestion;
public ImageView frmUserImgRound;
public ImageView imgvUserPic;
public Button btnFollowUnFollow;
}
}
这就是我在搜索活动中调用它的方式
public class SearchActivity extends ListActivity {
private TextView txtvName, txtvUsername;
private ImageView imgvUserPic;
private Button btnFollowUnFollow;
private ListView list;
private List<Post> userslist = new ArrayList<Post>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setContentView(R.layout.activity_search);
doMySearch("hello");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_search, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
// Get the intent, verify the action and get the query
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
doMySearch(query);
}
return super.onOptionsItemSelected(item);
}
public void doMySearch(String Query) {
class SendPostReqAsyncTask extends AsyncTask<Void, Void, String> {
ProgressDialog dialog;
// Show Progress bar before downloading Music
@Override
protected void onPreExecute() {
super.onPreExecute();
// Shows Progress Bar Dialog and then call doInBackground method
dialog = ProgressDialog.show(SearchActivity.this, "", "Loading. Please wait...", true);
}
@Override
protected String doInBackground(Void... params) {
HttpClient httpClient = new DefaultHttpClient();
StringBuilder url = new StringBuilder(MyAppUtil.API_URL); // Build URL as a String
String stUrlParams = "post/getUserHomeList/1/" + AppGlobal.currentUserId + "/25/0";
url.append(stUrlParams);
HttpGet httpGet = new HttpGet(url.toString());
try {
HttpResponse httpResponse = httpClient.execute(httpGet);
InputStream inputStream = httpResponse.getEntity().getContent();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
StringBuilder stringBuilder = new StringBuilder();
String bufferedStrChunk = null;
while ((bufferedStrChunk = bufferedReader.readLine()) != null) {
stringBuilder.append(bufferedStrChunk);
}
return stringBuilder.toString();
} catch (ClientProtocolException cpe) {
System.out.println("First Exception caz of HttpResponese :" + cpe);
cpe.printStackTrace();
} catch (IOException ioe) {
System.out.println("Second Exception caz of HttpResponse :" + ioe);
ioe.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(String result) {
// super.onPostExecute(result);
//close process dialog
if (this.dialog != null) {
this.dialog.dismiss();
}
//parse json
System.out.println(result);
JsonParser jsonParser = new JsonParser(result);
String message = jsonParser.getResponseMessage();
if (jsonParser.isSuccess()) {
System.out.println(message);
JSONArray postDataArr = jsonParser.getResponseDataRow(JsonParser.API_KEY_POST_DATASET);
System.out.println(postDataArr.length());
Post post = new Post();
// Parsing json
for (int i = 0; i < postDataArr.length(); i++) {
try {
userslist.add(post);
list = (ListView) findViewById(R.id.list1);
ListAdapter adapter = new SuggestionListAdapter(SearchActivity.this, userslist);
list.setAdapter(adapter);// line #153 here
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// Toast.makeText(SearchActivity.this, "You Clicked at " + userslist.get(+position).get("name"), Toast.LENGTH_SHORT).show();
}
});
// list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
// @Override
// public void onItemClick(AdapterView<?> parent, final View view,
// int position, long id) {
// final String item = (String) parent.getItemAtPosition(position);
// Log.v("SDSD", "DDFFFFFFF");
// }
// });
} catch (Exception e) {
e.printStackTrace();
}
}
} else {
MyAppUtil.getToast(getApplicationContext(), message);
}
}
}
SendPostReqAsyncTask sendPostReqAsyncTask = new SendPostReqAsyncTask();
sendPostReqAsyncTask.execute();
}
}
我的XML
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.almaarijsoft.kanvas.Activities.SearchActivity">
<ListView
android:id="@+id/list1"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</RelativeLayout>
和
<?xml version="1.0" encoding="utf-8"?><!--android:background="@drawable/selector_list_row"-->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="@color/gray_dark">
<LinearLayout
android:id="@+id/llUserInfo"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/black_gray"
android:orientation="vertical"
android:paddingBottom="5dp"
android:paddingLeft="5dp"
android:paddingRight="5dp"
android:paddingTop="5dp"
android:weightSum="1"
android:layout_marginLeft="0dp"
android:layout_marginTop="0dp"
android:layout_marginRight="0dp"
android:layout_marginBottom="1dp">
<!-- ========== START ROW1 ========== -->
<RelativeLayout
android:id="@+id/rltRow1"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<!-- User Picture Frame -->
<FrameLayout
android:id="@+id/frmUserImgRound"
android:layout_width="32dp"
android:layout_height="32dp"
android:layout_alignParentLeft="true"
android:layout_marginRight="8dp">
<ImageView
android:id="@+id/imgvUserPic"
android:layout_width="32dp"
android:layout_height="32dp"
android:layout_alignParentLeft="true"
android:layout_marginRight="8dp" />
<ImageView
android:layout_width="32dp"
android:layout_height="32dp"
android:src="@drawable/shap_round_frame_small_selector" />
</FrameLayout>
<!-- Username -->
<TextView
android:id="@+id/txtvUsernameSuggestion"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:layout_toRightOf="@+id/frmUserImgRound"
android:text="m.rashid.se"
android:textColor="@color/orange"
android:textSize="@dimen/post_description"
android:textStyle="bold" />
<Button
android:id="@+id/btnFollowUnFollow"
android:layout_width="100dp"
android:layout_height="25dp"
android:layout_alignParentRight="true"
android:layout_centerVertical="true"
android:background="@color/gray"
android:text="@string/btn_follow"
style="@style/AppTheme2"
/>
</RelativeLayout>
<!-- ========== END ROW1 ========== -->
<!-- ========== START ROW2 ========== -->
<RelativeLayout
android:id="@+id/rltRow2"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<!-- Username -->
<TextView
android:id="@+id/txtvNameSuggestion"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="40dp"
android:text="M. Rashid Hussain"
android:textColor="@color/gray"
android:textSize="@dimen/post_created_at"
android:textStyle="bold" />
</RelativeLayout>
</LinearLayout>
</RelativeLayout>
这些是我得到的警告。
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ java.lang.NullPointerException
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at com.almaarijsoft.kanvas.Activities.SearchActivity$1SendPostReqAsyncTask.onPostExecute(SearchActivity.java:153)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at com.almaarijsoft.kanvas.Activities.SearchActivity$1SendPostReqAsyncTask.onPostExecute(SearchActivity.java:89)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at android.os.AsyncTask.finish(AsyncTask.java:632)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:102)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at android.os.Looper.loop(Looper.java:136)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5579)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:515)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at dalvik.system.NativeStart.main(Native Method)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ java.lang.NullPointerException
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at com.almaarijsoft.kanvas.Activities.SearchActivity$1SendPostReqAsyncTask.onPostExecute(SearchActivity.java:153)
12-06 18:56:42.074 24567-24567/com.almaarijsoft.kanvas W/System.err﹕ at com.almaarijsoft.kanvas.Activities.SearchActivity$1SendPostReqAsyncTask.onPostExecute(SearchActivity.java:89)
答案 0 :(得分：1)
setContentView中的 SearchActivity已被注释掉，因此没有可通过findViewById找到的小部件。这就是NPE的原因。第二个错误是在适配器中实现getCount。它不应该返回0而是返回数据集的大小。 E.g。
@Override
public int getCount() {
return suggestion == null ? 0 : suggestion.size();
}
答案 1 :(得分：0)
避免在除了onCreate之外的任何地方加载XML布局。
此行返回null并应移动（或者您在此活动布局中没有list1 id）
getItem您还应该至少在BaseAdapter中实现getCount和{{1}}，或者切换到具有为您实现的ArrayAdapter。