Question

我在我的代码中配置了一个按钮来删除ListView中的一行，我认为它会起作用，但在离开页面后，数据才会重新出现。我已经看过一些关于如何做的帖子，但它很混乱，并想知道是否有人可以展示如何在setOnClickListener()

中实现删除方法

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

如果您的ID被指定为“TEAM_NUMBER”，那么您需要将其用于删除操作：

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。

更好的方法是这样的：

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

编辑：如何确定要删除的行

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();
        }
    });

Android - 删除数据库中的行

1 个答案: