[英]Passing variable “date” to another class via Intent on Android Studio, NULL OBJECT REFERENCE
[英]Android Studio - Passing variable with intent add extra, ends up with null
在修復了上一個問題的 null 指針異常后,(不確定是否可以為相同的代碼發布不同的問題,如果不是,請告訴我)我遇到了一個新問題。 當我嘗試將日期變量從第一個活動傳遞給另一個活動時,它始終為空。 我也試過設置一個公共吸氣劑或變量,它也是空的。 但是,使用 toast 檢查 class 表明該變量確實包含日期。 我正在嘗試通過應用程序 package 中的其他類將日期 class 添加到數據庫中。 任何幫助將非常感激。
日歷活動.java
package com.example.zaphk.studenthelperapplication3.calendar;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.CalendarView;
import android.widget.Toast;
import com.example.zaphk.studenthelperapplication3.R;
public class CalendarActivity extends AppCompatActivity {
public static final String EXTRA_TEXT = "com.example.zaphk.studenthelperapplication3";
private static final String TAG = "CalendarActivity";
private CalendarView mCalendarView;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.calendar_layout);
mCalendarView = (CalendarView) findViewById(R.id.calendarView);
mCalendarView.setOnDateChangeListener(new CalendarView.OnDateChangeListener() {
@Override
public void onSelectedDayChange(CalendarView CalendarView, int year, int month, int dayOfMonth) {
String date = year + "/" + month + "/"+ dayOfMonth ;
Log.d(TAG, "onSelectedDayChange: yyyy/mm/dd:" + date);
Intent intent = new Intent(CalendarActivity.this,CalendarEvent.class);
intent.putExtra(Intent.EXTRA_TEXT,date);
startActivity(intent);
Toast.makeText(CalendarActivity.this,date,Toast.LENGTH_SHORT).show();
}
});
}
}
class 我正在嘗試從以下位置接收它:CalendarEvent.java
package com.example.zaphk.studenthelperapplication3.calendar;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
import com.example.zaphk.studenthelperapplication3.calendar.database.Calendar;
import com.example.zaphk.studenthelperapplication3.calendar.database.CalendarAdapter;
import com.example.zaphk.studenthelperapplication3.calendar.database.Calendar_DbHelper;
import com.example.zaphk.studenthelperapplication3.utils.MyDividerItemDecoration;
import com.example.zaphk.studenthelperapplication3.utils.RecyclerTouchListener;
import com.example.zaphk.studenthelperapplication3.R;
public class CalendarEvent extends AppCompatActivity {
private CalendarAdapter mAdapter;
private List<Calendar> notesList = new ArrayList<>();
private CoordinatorLayout coordinatorLayout;
private RecyclerView recyclerView;
private TextView noNotesView;
Intent intent = getIntent();
public String date;
private Calendar_DbHelper db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
intent = getIntent();
date = intent.getStringExtra(CalendarActivity.EXTRA_TEXT);
setContentView(R.layout.activity_notes);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
coordinatorLayout = findViewById(R.id.coordinator_layout);
recyclerView = findViewById(R.id.recycler_view);
noNotesView = findViewById(R.id.empty_notes_view);
db = new Calendar_DbHelper(this);
notesList.addAll(db.getAllNotes());
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
showNoteDialog(false, null, -1);
}
});
mAdapter = new CalendarAdapter(this, notesList);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.addItemDecoration(new MyDividerItemDecoration(this, LinearLayoutManager.VERTICAL, 16));
recyclerView.setAdapter(mAdapter);
toggleEmptyNotes();
/**
* On long press on RecyclerView item, open alert dialog
* with options to choose
* Edit and Delete
* */
recyclerView.addOnItemTouchListener(new RecyclerTouchListener(this,
recyclerView, new RecyclerTouchListener.ClickListener() {
@Override
public void onClick(View view, final int position) {
}
@Override
public void onLongClick(View view, int position) {
showActionsDialog(position);
}
}));
}
/**
* Inserting new note in db
* and refreshing the list
*/
private void createNote(String note) {
// inserting note in db and getting
// newly inserted note id
long id = db.insertNote(note);
// get the newly inserted note from db
Calendar n = db.getNote(id);
if (n != null) {
// adding new note to array list at 0 position
notesList.add(0, n);
// refreshing the list
mAdapter.notifyDataSetChanged();
toggleEmptyNotes();
}
}
/**
* Updating note in db and updating
* item in the list by its position
*/
private void updateNote(String note, int position) {
Calendar n = notesList.get(position);
// updating note text
n.setNote(note);
// updating note in db
db.updateNote(n);
// refreshing the list
notesList.set(position, n);
mAdapter.notifyItemChanged(position);
toggleEmptyNotes();
}
/**
* Deleting note from SQLite and removing the
* item from the list by its position
*/
private void deleteNote(int position) {
// deleting the note from db
db.deleteNote(notesList.get(position));
// removing the note from the list
notesList.remove(position);
mAdapter.notifyItemRemoved(position);
toggleEmptyNotes();
}
/**
* Opens dialog with Edit - Delete options
* Edit - 0
* Delete - 0
*/
private void showActionsDialog(final int position) {
CharSequence colors[] = new CharSequence[]{"Edit", "Delete"};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Choose option");
builder.setItems(colors, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
if (which == 0) {
showNoteDialog(true, notesList.get(position), position);
} else {
deleteNote(position);
}
}
});
builder.show();
}
/**
* Shows alert dialog with EditText options to enter / edit
* a note.
* when shouldUpdate=true, it automatically displays old note and changes the
* button text to UPDATE
*/
private void showNoteDialog(final boolean shouldUpdate, final Calendar note, final int position) {
LayoutInflater layoutInflaterAndroid = LayoutInflater.from(getApplicationContext());
View view = layoutInflaterAndroid.inflate(R.layout.note_dialog, null);
AlertDialog.Builder alertDialogBuilderUserInput = new AlertDialog.Builder(CalendarEvent.this);
alertDialogBuilderUserInput.setView(view);
final EditText inputNote = view.findViewById(R.id.note);
TextView dialogTitle = view.findViewById(R.id.dialog_title);
dialogTitle.setText(!shouldUpdate ? getString(R.string.lbl_new_note_title) : getString(R.string.lbl_edit_note_title));
if (shouldUpdate && note != null) {
inputNote.setText(note.getNote());
}
alertDialogBuilderUserInput
.setCancelable(false)
.setPositiveButton(shouldUpdate ? "update" : "save", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogBox, int id) {
}
})
.setNegativeButton("cancel",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogBox, int id) {
dialogBox.cancel();
}
});
final AlertDialog alertDialog = alertDialogBuilderUserInput.create();
alertDialog.show();
alertDialog.getButton(AlertDialog.BUTTON_POSITIVE).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Show toast message when no text is entered
if (TextUtils.isEmpty(inputNote.getText().toString())) {
Toast.makeText(CalendarEvent.this, "Enter note!", Toast.LENGTH_SHORT).show();
return;
} else {
alertDialog.dismiss();
}
// check if user updating note
if (shouldUpdate && note != null) {
// update note by it's id
updateNote(inputNote.getText().toString(), position);
} else {
// create new note
createNote(inputNote.getText().toString());
}
}
});
}
/**
* Toggling list and empty notes view
*/
private void toggleEmptyNotes() {
// you can check notesList.size() > 0
if (db.getNotesCount() > 0) {
noNotesView.setVisibility(View.GONE);
} else {
noNotesView.setVisibility(View.VISIBLE);
}
}
public String getDate(){
return date;
}
}
您在活動之間傳遞數據時使用了錯誤的鍵。
替換下面的行,
intent.putExtra(Intent.EXTRA_TEXT,date);
有了這個,
intent.putExtra(CalendarActivity.EXTRA_TEXT,date);
您使用 Intent.EXTRA_TEXT 的鍵。
intent.putExtra(Intent.EXTRA_TEXT,date)
但是您使用另一個密鑰來接收。 這不是同一個鍵。
intent.getStringExtra(CalendarActivity.EXTRA_TEXT);
據我所知(不太確定)
Intent.EXTRA_TEXT
用於隱式意圖。
對於顯式(ieActivity 到 Activity)
執行以下操作
Intent intent = new Intent(CalendarActivity.this,CalendarEvent.class);
intent.putExtra("DATE",date);
startActivity(intent);
受到
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_notes);
intent = getIntent();
String date = intent.getStringExtra("DATE");
}
其中“日期”是字符串鍵。
我會說CalendarActivity.EXTRA_TEXT
可能是空的,因為您尚未將 class 導入CalendarEvent.java
import com.example.zaphk.studenthelperapplication3.calendar.CalendarActivity;
在CalendarEvent.java
正如其他人所說,Intent 上的 put 和 get 需要是相同的 String 值。
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