问题
I am working on android ListView and i am getting one issue.I created one list view into the XML file installation.xml and i want to use that list view into my Searchdata.java. so basically what i want that when i click on searchdata button than data is fetched from web service and after parsing, it will saved into the listview.and when i click on Installation View button than new window will be appear where i could see that list data.
SearchData.java
public class SearchData extends Activity {
EditText Keyword;
JSONParser jsonparser = new JSONParser();
ListView Datalist;
HorizontalScrollView VideoDatalist;
ArrayList<HashMap<String, String>> DataList;
ArrayList<HashMap<String, String>> VideoDataList;
JSONArray contacts = null;
private ProgressDialog pDialog;
ImageButton searchdata,InstallationView;
String Keyvalue = new String();
private static final String TAG_InnerText = "InnerText";
private static final String TAG_Title = "Title";
private static final String TAG_URL = "URL";
private static final String TAG_VIDEO_URL = "URL";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_search_data);
InstallationView=(ImageButton)findViewById(R.id.InstallationView);
Keyword = (EditText) findViewById(R.id.KeyData);
Datalist=(ListView)findViewById(R.layout.activity_installation);
VideoDatalist=(HorizontalScrollView)findViewById(R.id.Horizontallist);
searchdata=(ImageButton)findViewById(R.id.searchicon);
String Keyvalue = new String();
DataList = new ArrayList<HashMap<String, String>>();
VideoDataList = new ArrayList<HashMap<String, String>>();
searchdata.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
new ReadData().execute();
}
});
InstallationView.setOnClickListener(new View.OnClickListener(){
public void onClick(View v)
{
startActivity(new Intent(SearchData.this, Installation.class));
}
});
}
public class ReadData extends AsyncTask<Void, Void, Void>
{
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(SearchData.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
protected Void doInBackground(Void... arg0) {
try{
Keyvalue=Keyword.getText().toString();
String Jsonstr = jsonparser.makeHttpRequest("http://10.47.93.26:8080/Search/api/Search/"+Keyvalue);
try {
if (Jsonstr != null) {
JSONArray jsonObj = new JSONArray (Jsonstr);
for (int i = 0; i < jsonObj.length(); i++) {
JSONObject c = jsonObj.getJSONObject(i);
String name = c.optString(TAG_Title);
String url = c.optString(TAG_URL);
HashMap<String, String> info = new HashMap<String, String>();
if( !name.isEmpty() )
{
info.put(TAG_Title, name);
}
else
{
info.put(TAG_Title,"User Manual");
}
if(url.contains("youtube"))
{
info.put(TAG_URL, url);
VideoDataList.add(info);
}
else
{
info.put(TAG_URL, url);
DataList.add(info);
}
}
}
else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
}
catch (JSONException e) {
e.printStackTrace();
}
}
catch(Exception ex)
{
ex.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
if (pDialog.isShowing())
pDialog.dismiss();
SimpleAdapter adapter = new SimpleAdapter(
SearchData.this, DataList,
R.layout.list_item, new String[]
{
TAG_Title
}, new int[] {
R.id.InnerText });
Datalist.setAdapter(adapter);
}
}
}
web service running and parsing code is running correctly. i am getting error at post method,so can you help me on this.
Error
回答1:
In the onCreate(...) method of your SearchData Activity, the following can never work and will always return 'null' (hence your NullPointerException)...
Datalist=(ListView)findViewById(R.layout.activity_installation);
Calling findViewById(...) will only work for any UI elements which have been inflated when you called setContentView(...). In this case you used R.layout.activity_search_data for your layout file which doesn't contain a ListView with an id of R.layout.activity_installation which is, by the way, a resource id of a layout file and not a resource id of a UI element.
The only way you can do what you need is to put your data as an extra into the Intent you use when you call...
startActivity(new Intent(SearchData.this, Installation.class));
...when the Installation Activity is created it will then need to get the data and create its own adapter.
EDIT: HashMap is Serializable and can be passed as an Intent extra. Pass your DataList HashMap as follows...
Intent i = new Intent(SearchData.this, Installation.class);
i.putExtra("data_list", DataList);
startActivity(i);
In the Installation Activity you can then use...
getIntent().getSerializableExtra("data_list");
回答2:
Call your Installation activity in onClick() method:
And pass your ArrayList data through intent,
InstallationView.setOnClickListener(new View.OnClickListener(){
public void onClick(View v)
{
Intent intent= new Intent(SearchData.this, Installation.class);
intent.putParcelableArrayListExtra("HASH_MAP",DataList);
startActivity(intent);
}
});
In your Installation activity class,set the view in onCreate() and initialize listview from xml file:
setContentView(R.layout.activity_installation);
ListView listView = (ListView)findViwById(R.id.listview);
And try to get the data from intent:
ArrayList<HashMap<String,String>> hashmap_dataList = getIntent.getParcelableArrayListExtra("HASH_MAP");
then do whatever you want with listview and hashmap.
来源：https://stackoverflow.com/questions/29470136/how-to-use-listview-from-different-xml-layout-file