使用按钮单击更新 SQlite 数据库中的一行 [重复]

Posted 2023-04-19

【中文标题】使用按钮单击更新 SQlite 数据库中的一行 [重复]

【英文标题】：Update a row in SQlite database With Button Click [duplicate]

【发布时间】：2019-05-22 13:18:31

【问题描述】：

我有一个按钮，当我单击它时，我想将 SQLite 中的行字段设置为 1。该行的默认值为0。我想传递id，然后更新id的Liked行。我写的更新方法如下：

public void setLiked(long id) 
    walldb = this.getWritableDatabase() ;
    ContentValues values = new ContentValues();
    values.put(Colwall_Liked,1);
    walldb.update(TABLE_NAME , values, "=" + id,null) ;
    walldb.close();

这是我的 recyclerView 适配器类。

public class wallAdapter extends RecyclerView.Adapter<wallAdapter.ViewHolderWall> 

private Context ctx;
List<ModelWallpaper> modelWallpaper;
WallpaperHelper myHelper;

public wallAdapter(Context ctx, List<ModelWallpaper> modelWallpaper) 
    this.ctx = ctx;
    this.modelWallpaper = modelWallpaper;


@NonNull
@Override
public ViewHolderWall onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) 
    View view = LayoutInflater.from(ctx).inflate(R.layout.recyclerview_wallpaper,viewGroup,false);
    return new wallAdapter.ViewHolderWall(view);


@Override
public void onBindViewHolder(@NonNull ViewHolderWall viewHolderWall, int i) 
    final ModelWallpaper model = modelWallpaper.get(i);

    Glide.with(ctx)
            .load(model.getImageURL())
            .apply(new RequestOptions().centerCrop())
            .into(viewHolderWall.image);
    viewHolderWall.id = model.getID() ;

    viewHolderWall.setWall.setOnClickListener(new View.OnClickListener() 
        @Override
        public void onClick(View v) 

            Glide.with(ctx)
                    .asBitmap()
                    .load(model.getImageURL())
                    .into(new SimpleTarget<Bitmap>() 
                        @Override
                        public void onResourceReady(@NonNull Bitmap resource, @Nullable Transition<? super Bitmap> transition) 

                            try 
                                WallpaperManager.getInstance(ctx).setBitmap(resource) ;
                             catch (IOException e) 
                                e.printStackTrace();
                            
                        
                    );

        
    );





@Override
public int getItemCount() 
    return modelWallpaper.size();


class ViewHolderWall extends RecyclerView.ViewHolder 

private ImageView image;
private ShineButton heart;
private Button setWall;
long id;


public ViewHolderWall(View itemView) 
    super(itemView);

    image = itemView.findViewById(R.id.wallimage) ;
    heart = itemView.findViewById(R.id.po_image1);
    setWall = itemView.findViewById(R.id.setWall);

    final ModelWallpaper modelWallpaper = new ModelWallpaper();

    heart.setOnClickListener(new View.OnClickListener() 
        @Override
        public void onClick(View v) 
            if(modelWallpaper.getLiked() == 0) 
                myHelper.setLiked(id);
            
        
    );

我在 recyclerview Adapter 的 viewholder 类中编写了 onClick 方法。

long id; 

final ModelWallpaper modelWallpaper = new ModelWallpaper();

heart.setOnClickListener(new View.OnClickListener() 
        @Override
        public void onClick(View v) 
            if(modelWallpaper.getLiked() == 0) 
                myHelper.setLiked(id);
            
        
    );

这里是数据库 Hepler 类

public class WallpaperHelper extends SQLiteOpenHelper


SQLiteDatabase walldb ;

private static final String DATABASE_NAME = "Wallpaper.db" ;
private static final String TABLE_NAME = "Wallpaper_table" ;
private static final String Colwall_id = "ID" ;
private static final String Colwall_Url = "URL" ;
private static final String Colwall_Liked = "Liked" ;

public WallpaperHelper(Context context) 
    super(context, DATABASE_NAME, null, 1);




@Override
public void onCreate(SQLiteDatabase db) 
    String query = "create table if not exists " + TABLE_NAME + "(" + Colwall_id + " integer primary key autoincrement , " + Colwall_Url + " text not null , " + Colwall_Liked + " integer default 0" + ")";

    try 
        db.execSQL(query);
     catch (SQLException e) 
        e.printStackTrace();
    


@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    db.execSQL("drop table if exists " + TABLE_NAME);
    onCreate(db);

但是当我单击按钮时，应用程序强制停止。这是我的日志

   java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.hp.finalproject.Activities.Wallpaper.WallpaperHelper.setLiked(long)' on a null object reference
        at com.example.hp.finalproject.Activities.Wallpaper.wallAdapter$ViewHolderWall$1.onClick(wallAdapter.java:112)
        at com.sackcentury.shinebuttonlib.ShineButton$OnButtonClickListener.onClick(ShineButton.java:343)
        at android.view.View.performClick(View.java:5637)
        at android.view.View$PerformClick.run(View.java:22429)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

【问题讨论】：

onclick函数里面的id值是什么

viewHolderWall.id = model.getID() ;我在我的 onBind 视图持有者类中写了这个

请贴出完整代码

我已经编辑了我的代码。

onBindViewHolder里面的id是textview吗？？..你也正确初始化了myHelper吗？？@HedyehNz

【参考方案1】：

在您的ViewHolderWall 中初始化myHelper = new WallpaperHelper(ctx)

【讨论】：

哇，它成功了。你拯救了我的一天。谢谢

很高兴它帮助了您的健康