AsyncTask: une erreur est survenue lors de l'exécution doInBackground()

Question

Je tentais de faire application simple qui utilise AsyncTask pour enregistrer les données dans un SQLiteDatabase

Mise en page: activity_main

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 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:orientation="vertical" 
    android:layout_height="match_parent" 
    tools:context="jvtech.asynctask_practice.MainActivity"> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/name" 
     android:hint="name" 
    /> 

    <EditText 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/college" 
     android:hint="college" 
    /> 

    <Button 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/save" 
     android:text="save" 
    /> 

</LinearLayout> 

Classe principale: MainActivity.java

package jvtech.asynctask_practice; 

import android.content.Context; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 

public class MainActivity extends AppCompatActivity 
{ 
EditText name,college; 
String n,c; 
Button save; 
Context ct; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    name=(EditText)findViewById(R.id.name); 
    college=(EditText)findViewById(R.id.college); 
    save=(Button)findViewById(R.id.save); 
    save.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      n=name.getText().toString(); 
      c=college.getText().toString(); 
      BackgroundTask backgroundTask=new BackgroundTask(ct); 
      backgroundTask.execute("add_item",n,c); 
      finish(); 
     } 
    }); 
}} 

TableData.java

package jvtech.asynctask_practice; 

import android.provider.BaseColumns; 

public final class TableData { 
public TableData(){} 
public static abstract class TableInfo implements BaseColumns{ 
    public static final String NAME="name"; 
    public static final String COLLEGE="college"; 
    public static final String TABLE_NAME="info_user"; 
    public static final String DATABASE_NAME="info_reg"; 
}} 

DatabaseOperation.java

package jvtech.asynctask_practice; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.util.Log; 

public class DatabaseOperations extends SQLiteOpenHelper { 

public static final int database_version=1; 
public String CREATE_QUERY="CREATE TABLE "+TableData.TableInfo.TABLE_NAME+"("+TableData.TableInfo.NAME+" TEXT,"+TableData.TableInfo.COLLEGE+" TEXT);"; 

public DatabaseOperations(Context context) { 
    super(context, TableData.TableInfo.DATABASE_NAME, null, database_version); 
    Log.d("Database Operations","Database created"); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    db.execSQL(CREATE_QUERY); 
    Log.d("Database opeartions","Table Created"); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 

} 

public void putInformation(SQLiteDatabase sq,String name,String college) 
{ 
    ContentValues values=new ContentValues(); 
    values.put(TableData.TableInfo.NAME,name); 
    values.put(TableData.TableInfo.COLLEGE,college); 
    sq.insert(TableData.TableInfo.TABLE_NAME,null,values); 
    Log.d("Database Operations","One Row inserted"); 
}} 

BackgroundTask.java

package jvtech.asynctask_practice; 

import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.os.AsyncTask; 
import android.widget.Toast; 

public class BackgroundTask extends AsyncTask<String,String,String> { 
Context ct; 
BackgroundTask(Context ct) 
{ 
    this.ct=ct; 
} 
@Override 
protected void onPreExecute() { 
    super.onPreExecute(); 
} 

@Override 
protected String doInBackground(String... params) { 
    String method=params[0]; 
    DatabaseOperations db=new DatabaseOperations(ct); 
    if (method.equals("add_item")) 
    { 
     String n=params[1]; 
     String c=params[2]; 
     SQLiteDatabase sq=db.getWritableDatabase(); 
     db.putInformation(sq,n,c); 
    } 
    return "one row inserted"; 
} 

@Override 
protected void onProgressUpdate(String... values) { 
    super.onProgressUpdate(values); 
} 

@Override 
protected void onPostExecute(String s) { 
    Toast.makeText(ct,s, Toast.LENGTH_SHORT).show(); 
}} 

Erreurs:

 [use following link to see errors][https://i.stack.imgur.com/7i6Qr.png] 

Je joins et les fichiers que j'ai créé liés au projet. Je veux que le programme copie les données de EditTexts et les stocke dans SQLiteDatabse utilisant AsyncTask, mais j'obtiens une erreur. S'il vous plaît aider. Merci d'avance.

Answer 1

Vous n'attribuez jamais de valeur à , il s'agit donc de null lorsque vous créez votre BackgroundTask.