Android 如何在listview onCreate()中选择第一个索引?
我正在尝试在第一次加载onCreate时选择listview中的第一个索引。我尝试了listView.setSelection0,但出现了一些错误。这是我的密码Android 如何在listview onCreate()中选择第一个索引?,android,nullpointerexception,Android,Nullpointerexception,我正在尝试在第一次加载onCreate时选择listview中的第一个索引。我尝试了listView.setSelection0,但出现了一些错误。这是我的密码 public class QandAPractice extends AppCompatActivity { String qsid; ListView listView; ArrayList<String> myqid; RadioButton r1,r2,r3,r4; String txtcontent, txtTime
public class QandAPractice extends AppCompatActivity {
String qsid;
ListView listView;
ArrayList<String> myqid;
RadioButton r1,r2,r3,r4;
String txtcontent, txtTimer,txtAnskey,txtImg, txtA, txtB, txtC, txtD, txtID;
private static final String TAG_QID = "id";
private static final String TAG_TITLE = "content";
private static final String TAG_TIMER = "timer";
private static final String TAG_IMAGE = "images";
private static final String TAG_QSID = "qsid";
private static final String TAG_KEY = "key";
private static final String TAG_A = "A";
private static final String TAG_B = "B";
private static final String TAG_C = "C";
private static final String TAG_D = "D";
ArrayList<HashMap<String, String>> questions;
Dialog quizDialog;
public int i = 60;
public int loadindex = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_qand_apractice);
questions = new ArrayList<>();
myqid = new ArrayList<>();
Bundle b = getIntent().getExtras();
setTitle(b.getString("subject"));
qsid = b.getString("qsid");
quizDialog = new Dialog(this,android.R.style.Theme_Black_NoTitleBar_Fullscreen);
listView = findViewById(R.id.lvquestions);
getJSON(Constants.ROOT_URL+"mobile_question_index.php?qsid="+qsid);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
txtID = ((TextView) view.findViewById(R.id.quiz_id)).getText()
.toString();
txtcontent = ((TextView) view.findViewById(R.id.quiz_content)).getText()
.toString();
txtTimer = ((TextView) view.findViewById(R.id.quiz_timer)).getText()
.toString();
txtAnskey = ((TextView) view.findViewById(R.id.quiz_key)).getText()
.toString();
txtA = ((TextView) view.findViewById(R.id.quiz_A)).getText()
.toString();
txtB = ((TextView) view.findViewById(R.id.quiz_B)).getText()
.toString();
txtC = ((TextView) view.findViewById(R.id.quiz_C)).getText()
.toString();
txtD = ((TextView) view.findViewById(R.id.quiz_D)).getText()
.toString();
txtImg = ((TextView) view.findViewById(R.id.quiz_image)).getText()
.toString();
showQuiz();
}
});
listView.setSelection(0);
listView.getSelectedView().setSelected(true);
}
private void getJSON(final String urlWebService) {
class GetJSON extends AsyncTask<Void, Void, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
try {
loadIntoListView(s);
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
protected String doInBackground(Void... voids) {
try {
URL url = new URL(urlWebService);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
StringBuilder sb = new StringBuilder();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String json;
while ((json = bufferedReader.readLine()) != null) {
sb.append(json + "\n");
}
return sb.toString().trim();
} catch (Exception e) {
return null;
}
}
}
GetJSON getJSON = new GetJSON();
getJSON.execute();
}
private void loadIntoListView(String json) throws JSONException {
JSONArray jsonArray = new JSONArray(json);
//String[] question = new String[jsonArray.length()];
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject obj = jsonArray.getJSONObject(i);
String id = obj.getString(TAG_QID);
String content = obj.getString(TAG_TITLE);
String image = obj.getString(TAG_IMAGE);
String a = obj.getString(TAG_A);
String b = obj.getString(TAG_B);
String c = obj.getString(TAG_C);
String d = obj.getString(TAG_D);
String key = obj.getString(TAG_KEY);
String timer = obj.getString(TAG_TIMER);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_QID,id);
map.put(TAG_TITLE,content);
map.put(TAG_IMAGE,image);
map.put(TAG_A,a);
map.put(TAG_B,b);
map.put(TAG_C,c);
map.put(TAG_D,d);
map.put(TAG_KEY,key);
map.put(TAG_TIMER,timer);
myqid.add(id);
questions.add(map);
}
// ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, question);
SimpleAdapter adapter = new SimpleAdapter(
QandAPractice.this, questions,
R.layout.quizlayout, new String[]{TAG_QID,
TAG_TITLE, TAG_IMAGE,TAG_A,TAG_B,TAG_C,TAG_D,TAG_KEY,TAG_TIMER},
new int[]{R.id.quiz_id, R.id.quiz_content, R.id.quiz_image,R.id.quiz_A,R.id.quiz_B,
R.id.quiz_C,R.id.quiz_D,R.id.quiz_key,R.id.quiz_timer});
/* AtomicReference<ListAdapter> la =
new AtomicReference<>(new ListAdapter(getApplicationContext(), questions));*/
listView.setAdapter(adapter);
}
我读过一些和我有同样问题的帖子。他们使用适配器来解决这个问题,但在我的情况下,这个错误仍然会发生。非常感谢您的帮助。在将适配器设置为Listview后进行选择
private void loadIntoListView(String json) throws JSONException {
JSONArray jsonArray = new JSONArray(json);
//String[] question = new String[jsonArray.length()];
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject obj = jsonArray.getJSONObject(i);
String id = obj.getString(TAG_QID);
String content = obj.getString(TAG_TITLE);
String image = obj.getString(TAG_IMAGE);
String a = obj.getString(TAG_A);
String b = obj.getString(TAG_B);
String c = obj.getString(TAG_C);
String d = obj.getString(TAG_D);
String key = obj.getString(TAG_KEY);
String timer = obj.getString(TAG_TIMER);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_QID,id);
map.put(TAG_TITLE,content);
map.put(TAG_IMAGE,image);
map.put(TAG_A,a);
map.put(TAG_B,b);
map.put(TAG_C,c);
map.put(TAG_D,d);
map.put(TAG_KEY,key);
map.put(TAG_TIMER,timer);
myqid.add(id);
questions.add(map);
}
// ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, question);
SimpleAdapter adapter = new SimpleAdapter(
QandAPractice.this, questions,
R.layout.quizlayout, new String[]{TAG_QID,
TAG_TITLE, TAG_IMAGE,TAG_A,TAG_B,TAG_C,TAG_D,TAG_KEY,TAG_TIMER},
new int[]{R.id.quiz_id, R.id.quiz_content, R.id.quiz_image,R.id.quiz_A,R.id.quiz_B,
R.id.quiz_C,R.id.quiz_D,R.id.quiz_key,R.id.quiz_timer});
/* AtomicReference<ListAdapter> la =
new AtomicReference<>(new ListAdapter(getApplicationContext(), questions));*/
listView.setAdapter(adapter);
listView.setSelection(0);
listView.getSelectedView().setSelected(true);
}
我想我知道了你面临的主要问题。在填充列表视图之前,请尝试选择一个项目。您需要在listview上添加适配器后设置此选项。 在添加适配器后添加此行
listView.setAdapter(adapter);
listView.setSelection(0);
listView.getSelectedView().setSelected(true);
或使用
listView.setAdapter(adapter);
listView.setItemChecked(0, true)
这将显示首次开幕的祝酒词。这应该添加在适配器集之后
Iterator myVeryOwnIterator = questions.get(0).keySet().iterator();
while(myVeryOwnIterator.hasNext()) {
String key=(String)myVeryOwnIterator.next();
String value=(String)meMap.get(key);
Toast.makeText(ctx, "Key: "+key+" Value: "+value, Toast.LENGTH_LONG).show();
}
谢谢你的帮助,法兹·米尔先生。一个问题是,该错误始终指向此行listView.getSelectedView.setSelectedtrue;这对查看第一个索引的内容是否有必要?您试图实现的目标是什么?listView.getSelectedView.setSelectedtrue注释这一行并选中Yes sir我尝试注释掉这一行,但仍然要显示或甚至是toast数据来自listView中的第一个项目,并且没有出现错误。如果它有帮助,请接受答案谢谢sir,但是您可以确定如何显示或toast数据吗?我的意思是,如果我运行“活动”,它将自动调整listview中第一项的值。您希望显示哪些内容?您已经拥有包含map对象的问题列表。您可以很容易地从map对象中获取内容。感谢Faysal Ahmed爵士,我已经用以下代码找到了解决方案listView.performItemClicklistView.getAdapter.getView loadindex,null,null,loadindex,listView.getItemIdAtPositionloadindex;归功于所有者。此代码将起作用,但这不是正确的方法。您已经有了一个列表,为什么要单击某个项目并获取该列表?
Iterator myVeryOwnIterator = questions.get(0).keySet().iterator();
while(myVeryOwnIterator.hasNext()) {
String key=(String)myVeryOwnIterator.next();
String value=(String)meMap.get(key);
Toast.makeText(ctx, "Key: "+key+" Value: "+value, Toast.LENGTH_LONG).show();
}