Bitte sagen Sie mir, was in dem unten geschriebenen Code falsch ist

Question

Ich habe einen Code geschrieben, der eine Datenbank füllt. Allerdings, wenn ich diesen Code in meinem Android-Gerät oder Emulator ausführen, gibt es einen Fehler "Sorry app1 hat aufgehört zu arbeiten" Bitte helfen Sie mir herauszufinden, was los ist.

die MainActivity.java Datei

package cu_coders.app1; 

import android.net.Uri; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

import com.google.android.gms.appindexing.Action; 
import com.google.android.gms.appindexing.AppIndex; 
import com.google.android.gms.common.api.GoogleApiClient; 

public class MainActivity extends AppCompatActivity { 
    public final EditText e=(EditText)findViewById((R.id.text1)); 
    public final file1 f=new file1(); 
    TextView t=(TextView)findViewById(R.id.textView1); 
    final myDB x=new myDB(this, null, null, 1); 

    /** 
    * ATTENTION: This was auto-generated to implement the App Indexing API. 
    * See https://g.co/AppIndexing/AndroidStudio for more information. 
    */ 
    private GoogleApiClient client; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     // ATTENTION: This was auto-generated to implement the App Indexing API. 
     // See https://g.co/AppIndexing/AndroidStudio for more information. 
     client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build(); 
     Button enter=(Button)findViewById(R.id.button1); 
     Button delete=(Button)findViewById(R.id.button2); 
     enter.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       String s = e.getText().toString(); 
       f.set_name(s); 
       x.addItem(f); 
       t.setText(x.printTable()); 
      } 
     }); 
    } 
} 

eine Klasse FILE1.JAVA

package cu_coders.app1; 

/** 
* Created by user pc on 03-10-2016. 
*/ 
public class file1 { 
    private int _roll; 
    private String _name; 

    public file1() { 
    } 

    public file1(String _name) { 
     this._name = _name; 
    } 

    public int get_roll() { 
     return _roll; 
    } 

    public String get_name() { 
     return _name; 
    } 

    public void set_roll(int _roll) { 
     this._roll = _roll; 
    } 

    public void set_name(String _name) { 
     this._name = _name; 
    } 
} 

die Klasse für DATABASE MANAGEMENT-- myDB.java

package cu_coders.app1; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.DatabaseErrorHandler; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

/** 
* Created by user pc on 03-10-2016. 
*/ 
public class myDB extends SQLiteOpenHelper { 
    private static int DATABASE_VERSION=1; 
    private static String DATABASE_NAME="file.db"; 
    private static String TABLE_FILE1="class_cse"; 
    public static String COLUMN_KEY="_key"; 
    public static String COLUMN_NAME="_name"; 

    public myDB(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { 
     super(context, DATABASE_NAME, factory, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     String query="create table "+ TABLE_FILE1 + "(" + 
       COLUMN_KEY + " INTEGER PRIMARY KEY "+ 
       COLUMN_NAME+" TEXT "+ 
       ");"; 
     db.execSQL(query); 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_FILE1+";"); 
     onCreate(db); 

    } 
    public void addItem(file1 f){ 
     ContentValues cv=new ContentValues(); 
     cv.put(COLUMN_NAME,f.get_name()); 
     SQLiteDatabase db=getWritableDatabase(); 
     db.insert(TABLE_FILE1,null,cv); 
     db.close(); 
    } 
    /*public void deletItem(String item){ 
     SQLiteDatabase db=getWritableDatabase(); 
     db.execSQL("DELETE FROM "+TABLE_FILE1+" WHERE "+COLUMN_NAME+" =\" "+ item +"\";"); 
     db.close(); 
    } */ 
    public String printTable(){ 
     String dbstring=""; 
     SQLiteDatabase db=getWritableDatabase(); 
     String query="SELECT * FROM "+TABLE_FILE1+" WHERE 1;"; 
     Cursor c=db.rawQuery(query,null); 
     c.moveToFirst(); 
     while(!c.moveToLast()){ 
      if(c.getString(c.getColumnIndex(COLUMN_NAME))!=null) { 
       dbstring += c.getString(c.getColumnIndex(COLUMN_NAME)); 
       dbstring += '\n'; 
      } 
     } 
     db.close(); 
     return dbstring; 
    } 
} 

mir bitte helfen um herauszufinden, was falsch ist. Vielen Dank im Voraus.

Answer 1

sollten Sie mehrere Elemente ändern Ich denke, ...

Änderung myDB Constructor dazu:

public myDB(Context context) { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

und in mainActivity Klassenwechsel alle globalen Variablen wie folgt aus:

private EditText e ; 
private file1 f ; 
private TextView t; 

und in oncreate() initialisieren sie:

e=(EditText)findViewById((R.id.text1)); 
f=new file1(); 
t=(TextView)findViewById(R.id.textView1);