Android 如何访问RecyclerView'；s行'；s布局文件'；s
我的RecyclerView行中有一个开关小部件。我想访问该小部件以设置交换机上的setOnCheckedChangeListener，这样当我在mainActivity中的交换机上使用findViewById时，它就可以正常工作了。但是当我执行代码时，应用程序会因为这个错误而崩溃Android 如何访问RecyclerView'；s行'；s布局文件'；s,android,android-recyclerview,Android,Android Recyclerview,我的RecyclerView行中有一个开关小部件。我想访问该小部件以设置交换机上的setOnCheckedChangeListener，这样当我在mainActivity中的交换机上使用findViewById时，它就可以正常工作了。但是当我执行代码时，应用程序会因为这个错误而崩溃 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.raunak.alarmdemo4/com.raunak.alarmdem
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.raunak.alarmdemo4/com.raunak.alarmdemo4.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Switch.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference
public class MainActivity extends AppCompatActivity implements AlarmRecyclerViewInterface {
FloatingActionButton mAlarmAddButton;
RecyclerView mRecyclerView;
SQLiteDatabase db;
AlarmsDBhelperClass mAlarmsDBhelperClass;
ArrayList<String> nameArrayList = new ArrayList<>();
ArrayList <String> modeArrayList = new ArrayList<>();
ArrayList<String> repeatArrayList = new ArrayList<>();
ArrayList<String> hoursArrayList = new ArrayList<>();
ArrayList<String> minArrayList = new ArrayList<>();
Switch mSwitch;
AlarmAdapter.AlarmView mAlarmView;
AlarmAdapter alarmAdapter = new AlarmAdapter(hoursArrayList,minArrayList,modeArrayList,repeatArrayList,nameArrayList,this);
ImageView emptyImageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
//Initializing RecyclerView, DatabaseHelperClass, FAB button, The ON OFF switch & the empty ImageView
mAlarmsDBhelperClass = new AlarmsDBhelperClass(getApplicationContext());
mAlarmAddButton = findViewById(R.id.btnAlarmADD);
mRecyclerView = findViewById(R.id.alarmList);
mSwitch = findViewById(R.id.onoff);
emptyImageView = findViewById(R.id.empty_view);
//DividerItemDecoration class is used for getting a vertical line between rows of RecyclerView
DividerItemDecoration itemDecoration = new DividerItemDecoration(this,DividerItemDecoration.VERTICAL);
mRecyclerView.addItemDecoration(itemDecoration);
//Getting a writable reference of the Database.
db = mAlarmsDBhelperClass.getWritableDatabase();
//Retrieving values from the database and storing them in custom ArrayLists
boolean isDataEmpty = getAlarm(db);
//Checking if our arrayList is empty? if yes then display some empty list text or an image
if (!isDataEmpty){
mRecyclerView.setVisibility(View.GONE);
emptyImageView.setImageResource(R.drawable.no_alarm_black_white);
emptyImageView.setVisibility(View.VISIBLE);
}
else {
mRecyclerView.setVisibility(View.VISIBLE);
emptyImageView.setVisibility(View.GONE);
}
//FAB Event handling
mAlarmAddButton.setImageResource(R.drawable.addalarm);
mAlarmAddButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent mIntent = new Intent(getApplicationContext(), AddAlarm.class);
startActivity(mIntent);
}
});
mSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
if(b){
Calendar c = Calendar.getInstance();
c.set(Calendar.HOUR_OF_DAY, Integer.parseInt(hoursArrayList.get(mAlarmView.getAdapterPosition())));
c.set(Calendar.MINUTE, Integer.parseInt(minArrayList.get(mAlarmView.getAdapterPosition())));
c.set(Calendar.SECOND, 0);
startAlarm(c);
Toast.makeText(getApplicationContext(),"Alarm Turned ON !",Toast.LENGTH_SHORT).show();
}else{
cancelAlarm();
Toast.makeText(getApplicationContext(),"Alarm Turned OFF !",Toast.LENGTH_SHORT).show();
}
}
});
//Warping up with the recyclerView
mRecyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
mRecyclerView.setAdapter(alarmAdapter);
mRecyclerView.setHasFixedSize(true);
}
public boolean getAlarm(SQLiteDatabase db) {
Cursor cursor = db.rawQuery("SELECT * FROM alarms", new String[]{});
boolean rowExists;
if (cursor.moveToFirst()) {
do {
nameArrayList.add(cursor.getString(2));
modeArrayList.add(cursor.getString(3));
repeatArrayList.add(cursor.getString(4));
hoursArrayList.add(Integer.toString(cursor.getInt(5)));
minArrayList.add(Integer.toString(cursor.getInt(6)));
rowExists = true;
} while (cursor.moveToNext());
}else {
rowExists = false;
}
cursor.close();
return rowExists;
}
//RecyclerView's onClick()
@Override
public void onItemClick(int position) {
Toast.makeText(this, "Alarm Clicked !", Toast.LENGTH_SHORT).show();
}
//RecyclerView's onLongClick()
@Override
public void onLongItemClick(int position) {
//Updating the recyclerView
alarmAdapter.notifyItemRemoved(position);
//Deleting the row from the database
db.delete("alarms","alarm_name=?",new String[]{nameArrayList.get(position)});
hoursArrayList.remove(position);
Toast.makeText(this,"Alarm Deleted !", Toast.LENGTH_SHORT).show();
}
public void startAlarm(Calendar c){
//Getting a System service for the alarm to check the current time with the Alarm set time.
AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
//Creating an intent to invoke the onReceive method in the custom receiver class, just to display notifications.
Intent intent = new Intent(getApplicationContext(), AlarmReceiver.class);
//A pending intent is used to execute some work in the future with our applications permissions.
PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(),1,intent,0);
//Now RTC_WAKEUP means if the device is Switched off turn it on.
//getTimeInMillis() will get get the time in Milliseconds
//Schedule an alarm to be delivered precisely at the stated time.In my case it's the calendar's getTimeMillis() method. which is providing the correct time in milliseconds.
alarmManager.setExact(AlarmManager.RTC_WAKEUP,c.getTimeInMillis(),pendingIntent);
}
public void cancelAlarm(){
AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(getApplicationContext(),AlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(),1,intent,0);
//Now i'm cancelling the scheduled alarm using AlarmManager's cancel().
alarmManager.cancel(pendingIntent);
}
}
public类MainActivity扩展AppCompatActivity实现AlarmRecycleServiceInterface{
浮动操作按钮mAlarmAddButton；
回收视图mRecyclerView；
sqlitedb数据库；
报警SDBHELPERCLASS mAlarmsDBhelperClass；
ArrayList name ArrayList=新的ArrayList（）；
ArrayList modeArrayList=新建ArrayList（）；
ArrayList repeatArrayList=新的ArrayList（）；
ArrayList hoursArrayList=新建ArrayList（）；
ArrayList minArrayList=新的ArrayList（）；
开关；
AlarmAdapter.AlarmView-mAlarmView；
AlarmAdapter AlarmAdapter=新的AlarmAdapter（小时ArrayList、minArrayList、modeArrayList、repeatArrayList、nameArrayList、this）；
图像视图清空图像视图；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_main）；
setRequestedOrientation（ActivityInfo.SCREEN\u ORIENTATION\u Picture）；
//初始化RecyclerView、DatabaseHelperClass、FAB按钮、开关和空图像视图
mAlarmsDBhelperClass=新的报警SDBHELPERCLASS（getApplicationContext（））；
mAlarmAddButton=findViewById（R.id.btnalmadd）；
mRecyclerView=findviewbyd（R.id.alarmList）；
mSwitch=findviewbyd（R.id.onoff）；
emptyImageView=findViewById（R.id.empty\u视图）；
//DividerItemDecoration类用于获取RecyclerView行之间的垂直线
DividerItemDecoration=新的DividerItemDecoration（此为DividerItemDecoration.VERTICAL）；
mRecyclerView.附加装饰（项目装饰）；
//获取数据库的可写引用。
db=malarmsdbhelpersclass.getWritableDatabase（）；
//从数据库检索值并将其存储在自定义ArrayList中
布尔值isDataEmpty=getAlarm（db）；
//检查arrayList是否为空？如果是，则显示一些空列表文本或图像
如果（！isDataEmpty）{
mRecyclerView.setVisibility（View.GONE）；
emptyImageView.setImageResource（R.drawable.no_alarm_black_white）；
emptyImageView.setVisibility（View.VISIBLE）；
}
否则{
mRecyclerView.setVisibility（View.VISIBLE）；
emptyImageView.setVisibility（View.GONE）；
}
//FAB事件处理
mAlarmAddButton.setImageResource（R.drawable.addalarm）；
mAlarmAddButton.setOnClickListener（新视图.OnClickListener（）{
@凌驾
公共void onClick（视图）{
Intent MINENT=新的Intent（getApplicationContext（），AddAlarm.class）；
星触觉；
}
});
mSwitch.setOnCheckedChangeListener（新的CompoundButton.OnCheckedChangeListener（）{
@凌驾
检查更改后的公共无效（复合按钮复合按钮，布尔b）{
如果（b）{
Calendar c=Calendar.getInstance（）；
c、 set（Calendar.HOUR\u OF_DAY，Integer.parseInt（hoursArrayList.get（mAlarmView.getAdapterPosition（）））；
c、 set（Calendar.MINUTE、Integer.parseInt（minArrayList.get（mAlarmView.getAdapterPosition（）））；
c、 设置（日历秒，0）；
星形臂（c）；
Toast.makeText（getApplicationContext（），“报警已打开！”，Toast.LENGTH\u SHORT.show（）；
}否则{
取消报警（）；
Toast.makeText（getApplicationContext（），“报警已关闭！”，Toast.LENGTH\u SHORT.show（）；
}
}
});
//与recyclerView一起扭曲
setLayoutManager（新的LinearLayoutManager（getApplicationContext（））；
mRecyclerView.setAdapter（alarmAdapter）；
mRecyclerView.setHasFixedSize（true）；
}
公共布尔getAlarm（SQLiteDatabase db）{
Cursor Cursor=db.rawQuery（“从报警中选择*”，新字符串[]{}）；
布尔行存在；
if（cursor.moveToFirst（））{
做{
nameArrayList.add（cursor.getString（2））；
modeArrayList.add（cursor.getString（3））；
repeatArrayList.add（cursor.getString（4））；
添加（Integer.toString（cursor.getInt（5））；
add（Integer.toString（cursor.getInt（6））；
rowExists=true；
}while（cursor.moveToNext（））；
}否则{
rowExists=false；
}
cursor.close（）；
返回行存在；
}
//RecyclerView的onClick（）
@凌驾
公共空间单击（内部位置）{
Toast.makeText（这是“点击报警！”，Toast.LENGTH_SHORT.show（）；
}
//RecyclerView的onLongClick（）
@凌驾
public void onLongItemClick（内部位置）{
//更新recyclerView
alarmAdapter.NotifyItem已移除（位置）；
//正在从数据库中删除该行
delete（“alarms”，“alarm_name=？”，新字符串[]{nameArrayList.get（position）}）；
hoursArrayList.移除（位置）；
Toast.makeText（这是“已删除报警！”，Toast.LENGTH_SHORT.show（）；
}
公共空间startAlarm（日历c）{
//获取警报的系统服务，以检查当前时间与警报设置时间。
AlarmManager AlarmManager=（AlarmManager）getSystemService（Context.ALARM\u服务）；
//创建一个意图来调用自定义receiver类中的onReceive方法，只是为了显示通知。
意向意向=新意向（getApplicationContext（），AlarmReceiv）
<Switch
android:id="@+id/onoff"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="15dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.412" />
public class AlarmAdapter extends RecyclerView.Adapter<AlarmAdapter.AlarmView> {
//Variables for the main recycler view
private ArrayList<String> hoursArrayList;
private ArrayList<String> minArrayList;
private ArrayList<String> modeArrayList;
private ArrayList<String> repeatArrayList;
private ArrayList<String> nameArrayList;
private AlarmRecyclerViewInterface mInterface;
public AlarmAdapter(ArrayList<String> hours,ArrayList<String> mins,ArrayList<String> mode,ArrayList<String> repeat,ArrayList<String> name,AlarmRecyclerViewInterface mInterface){
this.hoursArrayList = hours;
this.minArrayList = mins;
this.modeArrayList = mode;
this.nameArrayList = name;
this.repeatArrayList = repeat;
this.mInterface = mInterface;
}
@NonNull
@Override
public AlarmView onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
View view = layoutInflater.inflate(R.layout.alarm_profile,parent,false);
return new AlarmView(view);
}
@Override
public void onBindViewHolder(@NonNull AlarmView holder, int position) {
if(Integer.parseInt(hoursArrayList.get(position)) < 10 ){
holder.hours.setText("0"+hoursArrayList.get(position));
}else {
holder.hours.setText(hoursArrayList.get(position));
}
if (Integer.parseInt(minArrayList.get(position)) < 10){
holder.mins.setText("0"+minArrayList.get(position));
}else {
holder.mins.setText(minArrayList.get(position));
}
holder.repeat.setText(repeatArrayList.get(position));
holder.mode.setText(modeArrayList.get(position));
holder.name.setText(nameArrayList.get(position));
}
@Override
public int getItemCount() {
return hoursArrayList.size();
}
/*ItemTouchHelper.SimpleCallback itemTouchHelperCallback = new ItemTouchHelper.SimpleCallback(0,ItemTouchHelper.RIGHT) {
@Override
public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
return false;
}
@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
nameArrayList.remove(viewHolder.getAdapterPosition());
modeArrayList.remove(viewHolder.getAdapterPosition());
repeatArrayList.remove(viewHolder.getAdapterPosition());
hoursArrayList.remove(viewHolder.getAdapterPosition());
minArrayList.remove(viewHolder.getAdapterPosition());
}
};*/
public class AlarmView extends RecyclerView.ViewHolder{
TextView hours,mins,repeat,name,mode;
public AlarmView(@NonNull View itemView) {
super(itemView);
hours = itemView.findViewById(R.id.txtHOUR);
mins = itemView.findViewById(R.id.txtMins);
repeat = itemView.findViewById(R.id.txtRepeatDays);
name = itemView.findViewById(R.id.txtName);
mode = itemView.findViewById(R.id.txtMode);
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
mInterface.onItemClick(getAdapterPosition());
}
});
itemView.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View view) {
mInterface.onLongItemClick(getAdapterPosition());
return true;
}
});
}
}
}
void startCancelAlarm(boolean isStart, int position);
mSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
mInterface.startCancelAlarm(b,getAdapterPosition());
}
});
^
@Override
public void startCancelAlarm(boolean isStart, int position) {
if(isStart){
Calendar c = Calendar.getInstance();
c.set(Calendar.HOUR_OF_DAY, Integer.parseInt(hoursArrayList.get(position)));
c.set(Calendar.MINUTE, Integer.parseInt(minArrayList.get(position)));
c.set(Calendar.SECOND, 0);
startAlarm(c);
Toast.makeText(getApplicationContext(),"Alarm Turned ON !",Toast.LENGTH_SHORT).show();
}else{
cancelAlarm();
Toast.makeText(getApplicationContext(),"Alarm Turned OFF !",Toast.LENGTH_SHORT).show();
}
}