Android - 删除数据库中的行

Question

我在我的代码中配置了一个按钮，用于删除ListView中的一行，我认为它可以工作，但离开页面后，数据就会重新出现。我已经看到了一堆关于如何做到这一点的职位，但它是非常令人困惑，想知道是否有人能说明如何实现的删除方法在setOnClickListener()

ListScoutInfoAdapter.java

import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.Button; 
import android.widget.TextView; 

import java.util.ArrayList; 
import java.util.List; 

public class ListScoutInfoAdapter extends ArrayAdapter { 

    List list = new ArrayList(); 
    DatabaseHelper databaseHelper; 
    SQLiteDatabase db = databaseHelper.getWritableDatabase(); 

    public ListScoutInfoAdapter (Context context, int resource) { 
     super(context, resource); 
    } //End of ListDataScoutInfoAdapter 

    static class LayoutHandler { 
     TextView TEAM_NUMBER, PORTCULLIS, CHEVAL_FRISE, MOAT, RAMPARTS, DRAWBRIDGE, SALLY_PORT, ROCK_WALL, ROCK_TERRAIN, LOW_BAR; 
    } //End of LayoutHandler 

    @Override 
    public void add(Object object) { 
     super.add(object); 
     list.add(object); 
    } //End of add 

    @Override 
    public int getCount() { 
     return list.size(); 
    } //End of getCount 

    @Override 
    public Object getItem(int position) { 
     return list.get(position); 
    } //End of getItem 

    public void deleteRow(){ 
     db.delete(DatabaseContract.NewDataInfo.TABLE_NAME, "id = '"+ DatabaseContract.NewDataInfo.COL_NUMBER +"'", null); 
    } //End of deleteRow 

    @Override 
    public View getView(final int position, View convertView, ViewGroup parent) { 
     View row = convertView; 
     LayoutHandler layoutHandler; 
     if (row == null){ 
      LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      row = layoutInflater.inflate(R.layout.row_layout, parent, false); 
      layoutHandler = new LayoutHandler(); 
      layoutHandler.TEAM_NUMBER = (TextView) row.findViewById(R.id.resultTeamNumber); 
      layoutHandler.PORTCULLIS = (TextView) row.findViewById(R.id.resultPortcullis); 
      layoutHandler.CHEVAL_FRISE = (TextView) row.findViewById(R.id.resultChevalFrise); 
      layoutHandler.MOAT = (TextView) row.findViewById(R.id.resultMoat); 
      layoutHandler.RAMPARTS = (TextView) row.findViewById(R.id.resultRamparts); 
      layoutHandler.DRAWBRIDGE = (TextView) row.findViewById(R.id.resultDrawbridge); 
      layoutHandler.SALLY_PORT = (TextView) row.findViewById(R.id.resultSallyPort); 
      layoutHandler.ROCK_WALL = (TextView) row.findViewById(R.id.resultRockWall); 
      layoutHandler.ROCK_TERRAIN = (TextView) row.findViewById(R.id.resultRockTerrain); 
      layoutHandler.LOW_BAR = (TextView) row.findViewById(R.id.resultLowBar); 
      row.setTag(layoutHandler); 
     } 
     else { 
      layoutHandler = (LayoutHandler) row.getTag(); 
     } //End of if statement 
     final DatabaseProvider databaseProvider = (DatabaseProvider) this.getItem(position); 
     layoutHandler.TEAM_NUMBER.setText(databaseProvider.getTeamNumber()); 
     layoutHandler.PORTCULLIS.setText(databaseProvider.getPortcullis()); 
     layoutHandler.CHEVAL_FRISE.setText(databaseProvider.getChevalFrise()); 
     layoutHandler.MOAT.setText(databaseProvider.getMoat()); 
     layoutHandler.RAMPARTS.setText(databaseProvider.getRamparts()); 
     layoutHandler.DRAWBRIDGE.setText(databaseProvider.getDrawbridge()); 
     layoutHandler.SALLY_PORT.setText(databaseProvider.getSallyPort()); 
     layoutHandler.ROCK_WALL.setText(databaseProvider.getRockWall()); 
     layoutHandler.ROCK_TERRAIN.setText(databaseProvider.getRockTerrain()); 
     layoutHandler.LOW_BAR.setText(databaseProvider.getLowBar()); 

     //Deletes ListView row 
     Button deleteBtn = (Button) row.findViewById(R.id.buttonDelete); 
     deleteBtn.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       list.remove(position); 
       notifyDataSetChanged(); 
      } //End of onClick 
     }); //End of setOnClickListener 

     return row; 
    } //End of getView 
} //End of class 

logcat的

03-17 13:57:33.715 4135-4135/com.compscitutorials.basigarcia.ramfernoscout E/AndroidRuntime: FATAL EXCEPTION: main 
                          Process: com.compscitutorials.basigarcia.ramfernoscout, PID: 4135 
                          java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.compscitutorials.basigarcia.ramfernoscout.DatabaseHelper.getWritableDatabase()' on a null object reference 
                           at com.compscitutorials.basigarcia.ramfernoscout.ListScoutInfoAdapter.<init>(ListScoutInfoAdapter.java:19) 
                           at com.compscitutorials.basigarcia.ramfernoscout.ScoutFragment.onCreateView(ScoutFragment.java:37) 
                           at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974) 
                           at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
                           at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252) 
                           at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) 
                           at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617) 
                           at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517) 
                           at android.os.Handler.handleCallback(Handler.java:739) 
                           at android.os.Handler.dispatchMessage(Handler.java:95) 
                           at android.os.Looper.loop(Looper.java:148) 
                           at android.app.ActivityThread.main(ActivityThread.java:5417) 
                           at java.lang.reflect.Method.invoke(Native Method) 
                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Answer 1

如果你的ID叫“TEAM_NUMBER”你表示，你需要使用删除操作：

public void deleteRow(String rowId){ 
    db.delete(DatabaseContract.NewDataInfo.TABLE_NAME, DatabaseContract.NewDataInfo.COL_NUMBER + "=" + rowId, null); 
} 

您需要将行ID传递给您的函数。

一个更好的办法，虽然是这样的：

public void deleteRow(String rowId){ 
    db.delete(DatabaseContract.NewDataInfo.TABLE_NAME, 
     DatabaseContract.NewDataInfo.COL_NUMBER + "=?", 
     new String[] {rowId}); 
} 

编辑：如何确定删除

Button deleteBtn = (Button) row.findViewById(R.id.buttonDelete); 
deleteBtn.setTag(databaseProvider.getTeamNumber()); 
    deleteBtn.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      deleteRow((String) v.getTag()); 
      list.remove(position); 
      notifyDataSetChanged(); 
     } 
    });