我正在开发一个Android应用程序，它从API读取数据，然后在多选对话框中显示这些数据。但是，当我单击该按钮时，该对话框为空。我想也许程序在volley返回响应之前执行下一行代码。我搜索了很多，但我不明白如何解决这个问题，我是使用Volley的初学者。
这是我从API获取数据的对话框代码：
public class LevelsDialog extends DialogFragment {
ArrayList<String> list = new ArrayList<>();
static String[] array;
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
array = getLevels();
final boolean[] checkedItems = new boolean[array.length];
builder.setTitle("Select Levels").setMultiChoiceItems(array, checkedItems, new DialogInterface.OnMultiChoiceClickListener() {
@Override
public void onClick(DialogInterface dialog, int which, boolean isChecked) {
if(isChecked) {
list.add(array[which]);
checkedItems[which] =true;
} else if(list.contains(array[which])) {
list.remove(array[which]);
checkedItems[which] = false;
}
}
}).setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
for(int i=0 ; i<list.size(); i++)
Log.e("After", "onClick: "+ list.get(i) );
}
});
return builder.create();
}
public String[] getLevels() {
final ArrayList<String> LevelsList = new ArrayList<>();
String url = Connection.URL + "/getAllLevels";
JsonArrayRequest objectRequest = new JsonArrayRequest(
Request.Method.GET,
url,
null,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
if (response.length() != 0) {
int length = response.length();
for (int i = 0; i < length; i++) {
try {
LevelsList.add(response.get(i).toString());
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("Rest Response Error ", error.toString());
}
});
Connection.getConnection(getActivity()).addToRequestQueue(objectRequest);
String[] Levels = LevelsList.toArray(new String[LevelsList.size()]);
return Levels;
}
}
任何的想法？谢谢。
您需要等待从您的截击请求中接收数据，然后允许用户点击多选对话框。
我想建议保留一个ProgressDialog在你的情况下，将显示，直到收到水平数据。因此，你的onCreateDialog将看起来像这样。
private ProgressDialog pD;
private final boolean[] checkedItems;
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
pD = new ProgressDialog(context);
pD.setMessage("Getting the levels information");
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setTitle("Select Levels").setMultiChoiceItems(array, checkedItems, new DialogInterface.OnMultiChoiceClickListener() {
@Override
public void onClick(DialogInterface dialog, int which, boolean isChecked) {
if(isChecked) {
list.add(array[which]);
checkedItems[which] =true;
} else if(list.contains(array[which])) {
list.remove(array[which]);
checkedItems[which] = false;
}
}
}).setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
for(int i=0 ; i<list.size(); i++)
Log.e("After", "onClick: "+ list.get(i) );
}
});
getLevels();
pD.show(); // Start showing the progress dialog
return builder.create();
}
现在修改你的getLevels函数。
public void getLevels() {
final ArrayList<String> LevelsList = new ArrayList<>();
String url = Connection.URL + "/getAllLevels";
JsonArrayRequest objectRequest = new JsonArrayRequest(
Request.Method.GET, url, null, new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
if (response.length() != 0) {
int length = response.length();
array = new int[length]; // Re-initialize the array
for (int i = 0; i < length; i++) {
try {
array[i] = response.get(i).toString();
} catch (JSONException e) {
e.printStackTrace();
}
}
pD.cancel();
checkedItems = new boolean[array.length];
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("Rest Response Error ", error.toString());
}
});
Connection.getConnection(getActivity()).addToRequestQueue(objectRequest);
}
希望有所帮助。
方法public String[] getLevels()不能立即返回数组，因为你正在向互联网做请求（这需要时间），所以，你需要使用一个回调接口，当凌空完成请求时，它会回调它并且仅在这次你会在屏幕上写
通用回调：
public interface ICallback<T> {
void onSucess(T result);
void onError(int code);
}
方法getLevels将为void，并带有回调参数
public void getLevels(final ICallback<String[]> callback) {
String url = Connection.URL + "/getAllLevels";
JsonArrayRequest objectRequest = new JsonArrayRequest(
Request.Method.GET,
url,
null,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
final ArrayList<String> LevelsList = new ArrayList<>();
if (response.length() != 0) {
int length = response.length();
for (int i = 0; i < length; i++) {
try {
LevelsList.add(response.get(i).toString());
} catch (JSONException e) {
e.printStackTrace();
}
}
}
String[] Levels = LevelsList.toArray(
new String[LevelsList.size()]);
callback.onSucess(Levels); //<-------- CALL IT BACK
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("Rest Response Error ", error.toString());
int code = -1;
if(error!=null){
if(error.networkResponse!=null){
code = error.networkResponse.statusCode;
}
}
callback.onError(code); // <-- ERROR
}
});
Connection.getConnection(getActivity()).addToRequestQueue(objectRequest);
}
因此，您将仅在回调中具有级别：
getLevels(
new ICallback<String[]>(){
@Override
public void onSucess(String[] result) {
// Create or update the dialog here...
}
@Override
public void onError(int errorCode) {
//error treatment...
}
}
);