我正在尝试构建一个可以从服务器获取某些信息的应用程序，以便我可以将其显示给用户。
我被告知将Volley视为一种方法。
我试图在片段中执行此操作，并且只有一个活动（Main_Activity），并且只需根据需要换出片段。
在我的登录片段中，我有以下代码：
public class loginFragment extends Fragment {
//Local Vars
private boolean loginCheck = false;
//required constructor
public loginFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_login, container, false);
}
//When login button is clicked, this method is called
private void login(View view) {
String username;
String password;
username = getView().findViewById(R.id.enteredUsername).toString();
password = getView().findViewById(R.id.enteredPassword).toString();
final ArrayList<String> info = new ArrayList<>();
String[] unameSeparated = new String[username.length()];
unameSeparated = username.split("(?!^)");
String startUrl = "https://us.api.battle.net/d3/profile/";
String uname = "";
String APIKey = "/?(pretend this is my API key)";
//Separating the username into the parts needed for sending request
for (int i = 0; i < unameSeparated.length; i++) {
if ((unameSeparated[i].equals("#"))) {
//Replacing # with '%23'
uname += "%23";
} else {
uname += unameSeparated[i];
}
}
String url = startUrl + uname+ APIKey;
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(getActivity());
// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
info.add(response);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});
// Add the request to the RequestQueue.
queue.add(stringRequest);
}
public boolean isLoggedIn() {
return loginCheck;
}
}
因此，当用户输入他们的用户名并点击登录按钮时，它应该将请求发送到服务器，并获取他们的数据并将其放入arraylist（我将更改它以将其放入文件以后我想，甚至只是一个变量）
目前设置方式，当我运行它时，单击登录按钮时出现错误，并显示：
04-28 18:55:40.358 6224-6224/com.hfad.diablo3assistant E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.hfad.diablo3assistant, PID: 6224
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:394)
at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:441)
at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:432)
at com.hfad.diablo3assistant.MainActivity.swapFragment(MainActivity.java:76)
at com.hfad.diablo3assistant.MainActivity.onOptionsItemSelected(MainActivity.java:48)
at android.app.Activity.onMenuItemSelected(Activity.java:3450)
at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:368)
at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
at android.support.v7.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:65)
at android.support.v7.widget.Toolbar$1.onMenuItemClick(Toolbar.java:202)
at android.support.v7.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:780)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:822)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:171)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:973)
at android.support.v7.view.menu.MenuPopup.onItemClick(MenuPopup.java:127)
at android.widget.AdapterView.performItemClick(AdapterView.java:318)
at android.widget.AbsListView.performItemClick(AbsListView.java:1158)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3127)
at android.widget.AbsListView$3.run(AbsListView.java:4042)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
选择菜单选项的主要活动代码：
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int item_id = item.getItemId();
switch (item_id) {
case R.id.accDetails:
swapFragment(item_id);
return true;
case R.id.personalProfileLookup:
swapFragment(item_id);
return true;
case R.id.favoriteCharacters:
swapFragment(item_id);
return true;
case R.id.friendProfileLookup:
swapFragment(item_id);
return true;
case R.id.tipsAndTricks:
swapFragment(item_id);
return true;
}
return false;
}
交换片段的主要活动代码：
private void swapFragment(int fragmentID){
TextView tracker = (TextView) findViewById(R.id.currentFragDisplay);
Fragment fragment = null;
if(fragmentID == R.id.personalProfileLookup) {
tracker.setText("My Profile");
fragment = new Personal_Profile_Fragment();
} else if(fragmentID == R.id.favoriteCharacters) {
tracker.setText("Favorite Characters");
fragment = new Favorite_Characters_Fragment();
} else if(fragmentID == R.id.friendProfileLookup) {
tracker.setText("Friend Lookup");
fragment = new Friend_Profile_Fragment();
} else if(fragmentID == R.id.tipsAndTricks) {
tracker.setText("Tips and Tricks");
fragment = new TipsandTricks_Fragment();
} else if(fragmentID == R.id.accDetails) {
tracker.setText("Log In");
fragment = new loginFragment();
}
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.fragmentContainer, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}