我想将数据从活动传输到片段，它总是打印此错误。我尝试使用不同的技术来克服这种想法，但仍然卡住了。我在活动或片段中的代码中遗漏了什么？
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.junaida.project1, PID: 14447
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.junaida.project1/com.example.junaida.project1.Year}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2957)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3018)
at android.app.ActivityThread.-wrap14(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1653)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6724)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
at com.example.junaida.project1.fragments.CardFragment.onCreateView(CardFragment.java:89)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2354)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1419)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1740)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1809)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:799)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2580)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2367)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2322)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2229)
at android.support.v4.app.FragmentManagerImpl.dispatchStateChange(FragmentManager.java:3221)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:3171)
at android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:192)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:560)
at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:177)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1256)
at android.app.Activity.performStart(Activity.java:6959)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2920)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3018)
at android.app.ActivityThread.-wrap14(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1653)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6724)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
这个错误指向
String id = bundle.getString("id");
我将列出从中传输数据的类
public class Year extends AppCompatActivity {
ImageView back;
GridView grid;
String id;
String type;
String year;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_year);
Intent data = getIntent();
year = data.getStringExtra("year");
id = data.getStringExtra("id");
type = data.getStringExtra("type");
BottomNavigationView bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);
//show the original color of icons
bottomNavigationView.setItemIconTintList(null);
bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
Fragment selectedFragment = null;
final Bundle bundle = new Bundle() ;
Intent intent;
switch (item.getItemId()) {
case R.id.action_item1:
bundle.putString("year",year);
bundle.putString("id",id);
bundle.putString("type",type);
//selectedFragment.setArguments(bundle);
selectedFragment = new CardFragment();
selectedFragment.setArguments(bundle);
break;
case R.id.action_item2:
bundle.putString("year",year);
bundle.putString("id",id);
bundle.putString("type",type);
//selectedFragment.setArguments(bundle);
selectedFragment = new AudioFragment();
selectedFragment.setArguments(bundle);
break;
case R.id.action_item3:
bundle.putString("year",year);
bundle.putString("id",id);
bundle.putString("type",type);
//selectedFragment.setArguments(bundle);
selectedFragment = new VideoFragment();
selectedFragment.setArguments(bundle);
break;
}
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.content_frame2, selectedFragment);
transaction.commit();
return true;
}
});
//Manually displaying the first fragment - one time only
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.content_frame2, new CardFragment());
transaction.commit();
back = (ImageView)findViewById(R.id.back_year);
back.setOnClickListener(new AdapterView.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), MainActivity.class);
startActivity(intent);
}
});
}
}
我的片段是
public class CardFragment extends Fragment {
// String id;
// String type;
// String year;
private ListAdapter adapter;
TextView textView;
private ListView lv;
private List<ListItemsData> list = new ArrayList<ListItemsData>();
private static final String url = "http://10.94.0.204/WebApplication7/api/subjects";
public CardFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle bundle = this.getArguments();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View rootView = inflater.inflate(R.layout.fragment_card, container, false);
//final ArrayList<ListItemsData> listItem = GetlistItems();
Bundle bundle = this.getArguments();
String id = bundle.getString("id");
String year = bundle.getString("year");
String type = bundle.getString("type");
final Activity mActivity = this.getActivity();
// lv.setAdapter(new ListAdapter(getActivity(), listItem));
adapter = new ListAdapter(getContext(), list);
lv.setAdapter(adapter);
try {
RequestQueue requestQueue = Volley.newRequestQueue(getContext());
String URL = "http://10.94.0.204/WebApplication7/api/subjects";
JSONObject jsonBody = new JSONObject();
// jsonBody.put("tblRegisteredUsers_nickName", username.getText().toString().trim());
jsonBody.put("id", id.toString());
jsonBody.put("Type", type.toString());
jsonBody.put("Year", year.toString());
final String requestBody = jsonBody.toString();
StringRequest stringRequest = new StringRequest(Request.Method.POST, URL, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
if (response.equals("success")) {
//login authenticated. Start the next activity of your app
Toast.makeText(getActivity(), response.toString(), Toast.LENGTH_LONG).show();
// Toast.makeText(getApplicationContext(), "registered successfully ", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(getActivity(), MainActivity.class);
// intent.putExtra("id", Id);
// intent.putExtra("year", year);
startActivity(intent);
} else {
//login failed. prompt to re-enter the credentials
Toast.makeText(mActivity.getApplicationContext(), "Failed to log In", Toast.LENGTH_SHORT).show();
Log.i("VOLLEY", response);
Toast.makeText(mActivity.getApplicationContext(), response.toString(), Toast.LENGTH_LONG).show();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("VOLLEY", error.toString());
}
})
{
@Override
public String getBodyContentType() {
return "application/json; charset=utf-8";
}
@Override
public byte[] getBody() throws AuthFailureError {
try {
return requestBody == null ? null : requestBody.getBytes("utf-8");
} catch (UnsupportedEncodingException uee) {
VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", requestBody, "utf-8");
return null;
}
}
@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
String responseString;
String json = null;
try {
json = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
responseString = String.valueOf(json).trim();
ArrayList<Response4> list_response = new ArrayList<Response4>();
Type listType = new TypeToken<List<Response4>>() {
}.getType();
list_response = new Gson().fromJson(responseString, listType);
//String check = list.get(0).getMessagesName();
for (int i = 0; i < list_response.size(); i++) {
// JSONObject obj = response.getJSONObject(i);
ListItemsData listItemData = new ListItemsData();
listItemData.setItem(list_response.get(i).getMessagesName());
listItemData.setUrl(list_response.get(i).getMessageURLNew());
//listItemData.setUrl((obj.getString("url")));
list.add(listItemData);
//Id = list.get(0).getId();
// year = list.get(0).getYear();
//Response2 yourModel = new Gson().fromJson(responseString, Response2.class);
}
// i should have this peice of code for methods that are in the background
getActivity().runOnUiThread(new Runnable() {
@Override
public void run() {
adapter.notifyDataSetChanged();
}
});
// String Check = yourModel.getMessagetitle();
return Response.success(list_response.toString(), HttpHeaderParser.parseCacheHeaders(response));
}
};
requestQueue.add(stringRequest);
} catch (JSONException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return rootView;
}
我以正确的方式发送数据吗？任何帮助，将不胜感激
从片段中获取bundle时，您应该使用getArguments（）。得到像这样的包
public View onCreateView(LayoutInflater inflater, ViewGroup containerObject,Bundle savedInstanceState){
//here is your arguments
Bundle bundle=getArguments();
//get string like this
String year = bundle.getString("year");
}
编辑：创建一个这样的函数并添加到您的默认片段以及从导航菜单开始的其他片段。
private Bundle getBundle(Intent data){
Bundle bundle = new Bundle();
bundle.putString("year",data.getStringExtra("year"));
bundle.putString("id",data.getStringExtra("id"));
bundle.putString("type",data.getStringExtra("type"));
}
这是最终的代码
public class Year extends AppCompatActivity {
ImageView back;
GridView grid;
String id;
String type;
String year;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_year);
Intent data = getIntent();
//get a bundle set and ready to use anytime
Bundle myBundle= getBundle(data);
BottomNavigationView bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);
//show the original color of icons
bottomNavigationView.setItemIconTintList(null);
bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
Fragment selectedFragment = null;
switch (item.getItemId()) {
case R.id.action_item1:
selectedFragment = new CardFragment();
selectedFragment.setArguments(myBundle);
break;
case R.id.action_item2:
selectedFragment = new AudioFragment();
selectedFragment.setArguments(myBundle);
break;
case R.id.action_item3:
selectedFragment = new VideoFragment();
selectedFragment.setArguments(myBundle);
break;
}
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.content_frame2, selectedFragment);
transaction.commit();
return true;
}
});
//Manually displaying the first fragment - one time only
CardFragment myCardFragment = new CardFragment();
myCardFragment.setArguments(myBundle);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.content_frame2, myCardFragment);
transaction.commit();
back = (ImageView)findViewById(R.id.back_year);
back.setOnClickListener(new AdapterView.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), MainActivity.class);
startActivity(intent);
}
});
}
private Bundle getBundle(Intent data){
Bundle bundle = new Bundle();
bundle.putString("year",data.getStringExtra("year"));
bundle.putString("id",data.getStringExtra("id"));
bundle.putString("type",data.getStringExtra("type"));
}
}