Java textview的SQLite android数据库错误
通过从数据库获取详细信息,我实现了一个Java textview的SQLite android数据库错误,java,android,android-studio,android-sqlite,Java,Android,Android Studio,Android Sqlite,通过从数据库获取详细信息,我实现了一个recyclerView,但我得到了一个错误。我是android应用程序开发新手,因此遇到问题请帮助纠正我的错误 代码如下: Cursor cursor1 =databse.rawQuery("select * from track_info where track_id1 = ? order by name desc",new String[]{pkg.getId()}); while (cursor1.moveToNex
recyclerView
,但我得到了一个错误。我是android应用程序开发新手,因此遇到问题请帮助纠正我的错误代码如下:
Cursor cursor1 =databse.rawQuery("select * from track_info where track_id1 = ? order by name desc",new String[]{pkg.getId()});
while (cursor1.moveToNext()){
location_data=findViewById(R.id.location_data);
activity_data=findViewById(R.id.activity_data);
time_data1=findViewById(R.id.time_data1);
time_data1.setText(cursor1.getString(1));
location_data.setText(cursor1.getString(2));
它在time_data1.setText(cursor1.getString(1))行上的指向错误代码>
错误是:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.randomfile.Track$1.onClick(Track.java:72)
RecycleViewadapter代码:
package com.example.fedexfinal;
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
public class RecycleviewAdapter extends RecyclerView.Adapter<RecycleviewAdapter.RecyclerViewHolder>{
private Context mContext;
public RecycleviewAdapter(Context context){
mContext= context;
}
public class RecyclerViewHolder extends RecyclerView.ViewHolder{
public RecyclerViewHolder(@NonNull View itemView) {
super(itemView);
}
}
@NonNull
@Override
public RecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(mContext);
View view=inflater.inflate(R.layout.recycle_item,parent,false);
return new RecyclerViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerViewHolder holder, int position) {
}
@Override
public int getItemCount() {
return 0;
}
}
package com.example.fedexfinal;
导入android.content.Context;
导入android.database.Cursor;
导入android.view.LayoutInflater;
导入android.view.view;
导入android.view.ViewGroup;
导入androidx.annotation.NonNull;
导入androidx.recyclerview.widget.recyclerview;
公共类RecycleView适配器扩展了RecycleView.Adapter{
私有上下文;
公共RecycleviewAdapter(上下文){
mContext=上下文;
}
公共类RecyclerView.ViewHolder扩展了RecyclerView.ViewHolder{
公共RecycleServiceWholder(@NonNull View itemView){
超级(项目视图);
}
}
@非空
@凌驾
public RecycleServiceWholder onCreateViewHolder(@NonNull ViewGroup父级,int-viewType){
LayoutFlater充气机=LayoutFlater.from(mContext);
视图=充气机。充气(右布局。回收项目,父项,false);
返回新的RecycleServiceWholder(视图);
}
@凌驾
BindViewHolder上的公共void(@NonNull RecycleServiceWholder holder,int位置){
}
@凌驾
public int getItemCount(){
返回0;
}
}
放置recycleviewer的XML代码
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".Track">
<RelativeLayout
android:id="@+id/relativeLayout1"
android:layout_width="0dp"
android:layout_height="0dp"
android:background="#ffffff"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="1.0">
<EditText
android:id="@+id/title_track"
android:layout_width="363dp"
android:layout_height="50dp"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginStart="18dp"
android:layout_marginLeft="18dp"
android:layout_marginTop="38dp"
android:background="#ffffff"
android:backgroundTint="#ffffff"
android:hint="Enter your Tracking Number"
android:inputType="text"></EditText>
<Button
android:id="@+id/trackbutton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginTop="99dp"
android:layout_marginEnd="161dp"
android:layout_marginRight="161dp"
android:text="Track"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
<TextView
android:id="@+id/textdata"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_marginTop="168dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Shipment Details"
android:textSize="24sp"
app:layout_constraintStart_toStartOf="parent" />
<TextView
android:id="@+id/textdata2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="207dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Dimension"
android:textSize="24sp"
app:layout_constraintStart_toStartOf="parent" />
<TextView
android:id="@+id/textdata3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="243dp"
android:ems="10"
android:inputType="text"
android:text="Weight"
android:textSize="24sp"
app:layout_constraintStart_toStartOf="parent" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycleview"
android:layout_width="408dp"
android:layout_height="453dp"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentBottom="true"
android:layout_marginStart="3dp"
android:layout_marginLeft="3dp"
android:layout_marginBottom="0dp" />
</RelativeLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
获取recycleview布局的xmlcode(recycle_item.xml):
有人能帮我了解错误并纠正我的错误吗请按照以下步骤解决问题:
型号:
public class TrackInfo implements Serializable {
private String locationData;
private String activityData;
private String timeData;
public TrackInfo(String location, String activity, String time) {
this.locationData = location;
this.activityData = activity;
this.timeData = time;
}
public String getLocationData() {
return locationData;
}
public String getActivityData() {
return activityData;
}
public String getTimeData() {
return timeData;
}
}
public class RecycleviewAdapter extends RecyclerView.Adapter<RecycleviewAdapter.RecyclerViewHolder>{
private List<TrackInfo> trackInfoList;
public RecycleviewAdapter(List<TrackInfo> tracks){
trackInfoList= tracks;
}
class RecyclerViewHolder extends RecyclerView.ViewHolder{
private TextView locationView, activityView, timeView;
public RecyclerViewHolder(@NonNull View itemView) {
super(itemView);
locationView = itemView.findViewById(R.id.location_data);
activityView = itemView.findViewById(R.id.activity_data);
timeView = itemView.findViewById(R.id.time_data1);
}
}
@NonNull
@Override
public RecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycle_item,parent,false);
return new RecyclerViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerViewHolder holder, int position) {
TrackInfo trackInfo = trackInfoList.get(position);
holder.activityView.setText(trackInfo.getActivityData());
holder.locationView.setText(trackInfo.getLocationData());
holder.timeView.setText(trackInfo.getTimeData());
}
@Override
public int getItemCount() {
return trackInfoList.size();
}
}
活动:
public class TrackActivity extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
List<TrackInfo> trackInfoList = getData();
RecyclerView recyclerView = findViewById(R.id.recycleview);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(new RecycleviewAdapter(trackInfoList));
}
public List<TrackInfo> getData() {
List<TrackInfo> trackInfoList = new ArrayList<>();
Cursor cursor1 = databse.rawQuery("select * from track_info where track_id1 = ? order by name desc",new String[]{pkg.getId()});
while (cursor1.moveToNext()) {
String time = cursor1.getString(1);
String location = cursor1.getString(2);
String activity = cursor1.getString(3);
trackInfoList.add(new TrackInfo(location, activity, time));
}
return trackInfoList;
}
}
公共类TrackActivity扩展了AppCompatActivity{
@凌驾
创建时受保护的void(@Nullable Bundle savedInstanceState){
super.onCreate(savedInstanceState);
...
List trackInfoList=getData();
recycleview recycleview=findViewById(R.id.recycleview);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(新的LinearLayoutManager(本));
setAdapter(新的RecycleviewAdapter(trackInfoList));
}
公共列表getData(){
List trackInfoList=new ArrayList();
游标cursor1=database.rawQuery(“从track_info中选择*其中track_id1=?按名称排序desc”,新字符串[]{pkg.getId()});
while(cursor1.moveToNext()){
字符串时间=cursor1.getString(1);
字符串位置=cursor1.getString(2);
字符串活动=cursor1.getString(3);
添加(新的TrackInfo(位置、活动、时间));
}
返回trackInfoList;
}
}
适配器:
public class TrackInfo implements Serializable {
private String locationData;
private String activityData;
private String timeData;
public TrackInfo(String location, String activity, String time) {
this.locationData = location;
this.activityData = activity;
this.timeData = time;
}
public String getLocationData() {
return locationData;
}
public String getActivityData() {
return activityData;
}
public String getTimeData() {
return timeData;
}
}
public class RecycleviewAdapter extends RecyclerView.Adapter<RecycleviewAdapter.RecyclerViewHolder>{
private List<TrackInfo> trackInfoList;
public RecycleviewAdapter(List<TrackInfo> tracks){
trackInfoList= tracks;
}
class RecyclerViewHolder extends RecyclerView.ViewHolder{
private TextView locationView, activityView, timeView;
public RecyclerViewHolder(@NonNull View itemView) {
super(itemView);
locationView = itemView.findViewById(R.id.location_data);
activityView = itemView.findViewById(R.id.activity_data);
timeView = itemView.findViewById(R.id.time_data1);
}
}
@NonNull
@Override
public RecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycle_item,parent,false);
return new RecyclerViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerViewHolder holder, int position) {
TrackInfo trackInfo = trackInfoList.get(position);
holder.activityView.setText(trackInfo.getActivityData());
holder.locationView.setText(trackInfo.getLocationData());
holder.timeView.setText(trackInfo.getTimeData());
}
@Override
public int getItemCount() {
return trackInfoList.size();
}
}
公共类RecycleView适配器扩展了RecycleView.Adapter{
私有列表trackInfoList;
公共回收设施(列出轨道){
trackInfoList=轨道;
}
类RecyclerViewHolder扩展了RecyclerView.ViewHolder{
私有文本视图位置视图、活动视图、时间视图;
公共RecycleServiceWholder(@NonNull View itemView){
超级(项目视图);
locationView=itemView.findViewById(R.id.location\U数据);
activityView=itemView.findViewById(R.id.activity\U数据);
timeView=itemView.findviewbyd(R.id.time\u data1);
}
}
@非空
@凌驾
public RecycleServiceWholder onCreateViewHolder(@NonNull ViewGroup父级,int-viewType){
View=LayoutFlater.from(parent.getContext()).flate(R.layout.recycle_项,parent,false);
返回新的RecycleServiceWholder(视图);
}
@凌驾
BindViewHolder上的公共void(@NonNull RecycleServiceWholder holder,int位置){
TrackInfo TrackInfo=trackInfoList.get(位置);
holder.activityView.setText(trackInfo.getActivityData());
holder.locationView.setText(trackInfo.getLocationData());
holder.timeView.setText(trackInfo.getTimeData());
}
@凌驾
public int getItemCount(){
返回trackInfoList.size();
}
}
更改此代码
time_data1=findViewById(R.id.time_data1);
与
如果您的代码位于数据库帮助器类中-
Cursor cursor1 =databse.rawQuery("select * from track_info where track_id1 = ? order by name desc",new String[]{pkg.getId()});
while (cursor1.moveToNext()){
location_data=findViewById(R.id.location_data);
activity_data=findViewById(R.id.activity_data);
time_data1=findViewById(R.id.time_data1);
time_data1.setText(cursor1.getString(1));
location_data.setText(cursor1.getString(2));
而不仅仅是这样-
public List<String> getData(){
Cursor cursor1 =databse.rawQuery("select * from track_info where track_id1 = ? order by name desc",new String[]{pkg.getId()});
List<String> data = new ArrayList();
while (cursor1.moveToNext()){
data.add(cursor1.getString(1))
}
return data
}
如果您在recyclerview中使用此数据,请将列表传递到recyclerview适配器。感谢您回答先生,但它已在上一条语句本身time\u data1=findViewById(r.id.time\u data1)中初始化;在初始化日志后添加一个日志,如-log.d(标记“isnull”+(time\u data1==null)+++(location\u data==null));确认它们不是空的。谢谢你的回复。是的,它显示空的,怎么办@NareshNK@BhavinThakar,请发布包含xml的最小代码以获取帮助。在不知道您在代码中做什么的情况下,我们如何说出解决方案?您是在片段活动中调用上述代码的吗??发布更多的代码,如您正在使用此代码的哪个部分。请提供一个最小的可复制示例:。您能提供xml代码吗?请提供check@Md.Asaduzzaman,@swayangjit为什么onBindViewHolder为空?从哪里设置文本视图?你必须展示你的能力code@BhavinThakar,您实施RecyclerView的方法不正确。请从那里获得帮助:
time_data1=findViewById(R.id.time_data1);
time_data1.setText(cursor1.getString(1));