在通过recyclerView从SQLite显示片段中的数据时遇到问题。当我点击showfragment按钮它崩溃并显示“不幸的应用程序停止”。它有6个java类和4个xml 我在下面给出了我的代码
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
public class DbHelperAdapter{
DbHelper helper;
public DbHelperAdapter(Context context){
helper=new DbHelper(context);
}
public long insetData(String name,String password){
SQLiteDatabase db=helper.getWritableDatabase();
ContentValues contentValues=new ContentValues();
contentValues.put(DbHelper.NAME,name);
contentValues.put(DbHelper.PASSWORD,password);
long id=db.insert(DbHelper.TABLE_NAME,null,contentValues);
db.close();
return id;
}
public String getAllData(){
SQLiteDatabase db= helper.getWritableDatabase();
String[] columns={DbHelper.UID,DbHelper.NAME,DbHelper.PASSWORD};
Cursor cursor=db.query(DbHelper.TABLE_NAME, columns, null, null, null, null, null);
StringBuffer buffer = new StringBuffer();
while (cursor.moveToNext()){
int cid=cursor.getInt(cursor.getColumnIndex(DbHelper.UID));
String name = cursor.getString(cursor.getColumnIndex(DbHelper.NAME));
String pass = cursor.getString(cursor.getColumnIndex(DbHelper.PASSWORD));
buffer.append(cid+" "+name+" "+pass+"\n");
}
return buffer.toString();
}
public List<Information> getAllData_a(){
SQLiteDatabase db= helper.getWritableDatabase();
String[] columns={DbHelper.UID,DbHelper.NAME,DbHelper.PASSWORD};
Cursor cursor=db.query(DbHelper.TABLE_NAME, columns, null, null, null, null, null);
List<Information> data=new ArrayList<>();
while (cursor.moveToNext()){
int cid=cursor.getInt(cursor.getColumnIndex(DbHelper.UID));
String name = cursor.getString(cursor.getColumnIndex(DbHelper.NAME));
String pass = cursor.getString(cursor.getColumnIndex(DbHelper.PASSWORD));
Information current = new Information();
current.u_id=cid;
current.user=name;
current.pass=pass;
data.add(current);
}
return data;
}
public String getData(String name){
SQLiteDatabase db= helper.getWritableDatabase();
String[] columns={DbHelper.NAME,DbHelper.PASSWORD};
Cursor cursor=db.query(DbHelper.TABLE_NAME, columns, DbHelper.NAME+" = '"+name+"' ", null, null, null, null);
StringBuffer buffer = new StringBuffer();
while (cursor.moveToNext()){
String PersonName = cursor.getString(cursor.getColumnIndex(DbHelper.NAME));
String pass = cursor.getString(cursor.getColumnIndex(DbHelper.PASSWORD));
buffer.append(PersonName+" "+pass+"\n");
}
return buffer.toString();
}
static class DbHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "demo";
private static final String TABLE_NAME = "tbl_demo";
private static final int VERSION_NAME=3;
private static final String UID="_id";
private static final String NAME="name";
private static final String PASSWORD="Password";
private static final String CREATE_TABLE="CREATE TABLE "+TABLE_NAME+" ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+NAME+" VARCHAR(255),"+PASSWORD+" VARCHAR(255));";
private static final String DROP_TABLE="DROP TABLE IF EXISTS "+TABLE_NAME+"";
private Context context;
public DbHelper(Context context){
super(context,DATABASE_NAME,null,VERSION_NAME);
this.context=context;
Message.message(context, "constructorCalled");
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(CREATE_TABLE);
Message.message(context, "onCreateCalled");
}catch (android.database.SQLException e){
Message.message(context, ""+e);
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
try {
Message.message(context, "onUpgradeCalled");
db.execSQL(DROP_TABLE);
onCreate(db);
} catch (android.database.SQLException e) {
Message.message(context, ""+e);
}
}
}
}
public class Information {
int u_id;
String user;
String pass;}
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.support.v4.app.Fragment;
public class MainActivity extends ActionBarActivity {
DbHelperAdapter dbHelperAdapter;
EditText userName;
EditText password;
EditText selectionName;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelperAdapter = new DbHelperAdapter(this);
userName= (EditText) findViewById(R.id.username);
password= (EditText) findViewById(R.id.password);
selectionName= (EditText) findViewById(R.id.selection_name);
}
public void addUser(View view){
String user = userName.getText().toString();
String pass = password.getText().toString();
long id = dbHelperAdapter.insetData(user,pass);
if(id<0){
Message.message(this,"Unsuccessful");
}
else {
Message.message(this,"Successfully insert A Row");
}
}
public void getTheFragment(View view){
Intent i= new Intent(this,MainActivity2.class);
startActivity(i);
}
public void viewDetails(View view){
String data=dbHelperAdapter.getAllData();
Message.message(this,data);
}
public void getDataBySelection(View view){
String name = selectionName.getText().toString();
String selections=dbHelperAdapter.getData(name);
Message.message(this,selections);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}}
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
public class MainActivity2 extends ActionBarActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_activity2);
ViewPager pager = (ViewPager) findViewById(R.id.viewPager);
pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
}
private class MyPagerAdapter extends FragmentPagerAdapter {
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int pos) {
return new MyFragment();
}
@Override
public int getCount() {
return 1;
}
}}
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
public class MyFragment extends Fragment {
RecyclerView recyclerView;
RecyclerViewAdapter adapter;
DbHelperAdapter dbHelperAdapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View layout=inflater.inflate(R.layout.fragment_new, container, false);
recyclerView = (RecyclerView) layout.findViewById(R.id.list);
adapter = new RecyclerViewAdapter(getActivity(),dbHelperAdapter.getAllData_a());
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
return layout;
}}
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.text.Layout;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.Collections;
import java.util.List;
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> {
private LayoutInflater inflater;
List<Information> data= Collections.emptyList();
public RecyclerViewAdapter(Context context, List<Information> data){
inflater = LayoutInflater.from(context);
this.data =data;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view=inflater.inflate(R.layout.custom_raw,parent,false);
MyViewHolder holder=new MyViewHolder(view);
return holder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
Information current = data.get(position);
holder.UID.setText(current.u_id);
holder.USER.setText(current.user);
holder.PASS.setText(current.pass);
}
@Override
public int getItemCount() {
return data.size();
}
class MyViewHolder extends RecyclerView.ViewHolder {
TextView UID;
TextView USER;
TextView PASS;
public MyViewHolder(View itemView) {
super(itemView);
UID= (TextView) itemView.findViewById(R.id.u_id);
USER = (TextView) itemView.findViewById(R.id.user);
PASS = (TextView) itemView.findViewById(R.id.pass);
}
}}
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity"
android:orientation="vertical">
<EditText
android:id="@+id/username"
android:layout_width="match_parent"
android:layout_height="wrap_content"
/>
<EditText
android:id="@+id/password"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/editText"
/>
<Button
android:id="@+id/button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/editText2"
android:onClick="addUser"
android:text="@string/add_user" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:onClick="viewDetails"
android:text="View Details"
android:id="@+id/view_details_btn"
android:layout_gravity="center_horizontal" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/selection_name"
android:layout_gravity="center_horizontal" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="GetSelectedData"
android:onClick="getDataBySelection"
android:id="@+id/getDataBySelection" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Show Fragment"
android:onClick="getTheFragment"
android:id="@+id/show_fragment"
/>
</LinearLayout>
<android.support.v4.view.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/viewPager"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/u_id"
android:layout_gravity="center"
android:text="UID"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/user"
android:layout_gravity="center"
android:text="NAME"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/pass"
android:layout_gravity="center"
android:text="PASSWORD"/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</android.support.v7.widget.RecyclerView>
</RelativeLayout>
google drive link：https://drive.google.com/folderview?id=0B0uBfXsWeMlgX0U5OE8tREhxQkk&usp=sharing
logcat错误：
02-02 22:15:27.455 10562-10562/com.maticoders.databasetest E/AndroidRuntime? FATAL EXCEPTION: main
java.lang.NullPointerException
at com.maticoders.databasetest.MyFragment.onCreateView(MyFragment.java:29)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
at android.view.View.measure(View.java:15635)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4919)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:15635)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4919)
at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:453)
at android.view.View.measure(View.java:15635)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4919)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:15635)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4919)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1411)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:698)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
at android.view.View.measure(View.java:15635)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4919)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2200)
at android.view.View.measure(View.java:15635)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2165)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1249)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1443)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1139)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4872)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:776)
at android.view.Choreographer.doCallbacks(Choreographer.java:579)
at android.view.Choreographer.doFrame(Choreographer.java:548)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:762)
at android.os.Handler.handleCallback(Handler.java:800)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5371)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
错误发生在我的RecyclerViewAdapter类中 我没有传递上下文并在textView中传递一个整数 这是我的RecylerViewAdapter类
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.text.Layout;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.Collections;
import java.util.List;
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> {
private Context context;
private LayoutInflater inflater;
List<Information> data= Collections.emptyList();
public RecyclerViewAdapter(Context context, List<Information> data){
this.context=context;
inflater = LayoutInflater.from(context);
this.data =data;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view=inflater.inflate(R.layout.custom_raw,parent,false);
MyViewHolder holder=new MyViewHolder(view);
return holder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
Information current = data.get(position);
holder.UID.setText(String.valueOf(current.u_id));
holder.USER.setText(current.user);
holder.PASS.setText(current.pass);
}
@Override
public int getItemCount() {
return data.size();
}
class MyViewHolder extends RecyclerView.ViewHolder {
TextView UID;
TextView USER;
TextView PASS;
public MyViewHolder(View itemView) {
super(itemView);
UID= (TextView) itemView.findViewById(R.id.u_id);
USER = (TextView) itemView.findViewById(R.id.user);
PASS = (TextView) itemView.findViewById(R.id.pass);
}
}
}