从FirebaseRecyclerAdapter获取文档ID并传递价值，以新的一页

Question

我有显示的文件列表的FirestoreRecyclerAdapter。我在列表中的每个项目旁边的按钮。在点击这个按钮，我想这是选择的项目的唯一ID，然后将用户带到显示该项目的个人详细信息的页面。

基本上我想通过点击下页文档的ID。然而，当点击我的按钮抛出一个空指针异常。

此代码是从我ClubAdapter类。

public class ClubAdapter1 extends FirestoreRecyclerAdapter<Club, ClubAdapter1.ClubHolder> {

    private String clubId;
    private Context context;

    public ClubAdapter1(@NonNull FirestoreRecyclerOptions<Club> options) {
        super(options);
    }

    @Override
    protected void onBindViewHolder(@NonNull ClubHolder holder, int position, @NonNull Club model) {
        holder.lblName.setText(model.getClubName());
        //getting the ID of the particular event clicked
        clubId = getSnapshots().getSnapshot(position).getId();

        holder.btnDetails.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(context, ViewSingleClub.class);
                i.putExtra("id", clubId);
                context.startActivity(i);
            }
        });
    }

    @NonNull
    @Override
    public ClubHolder onCreateViewHolder(@NonNull ViewGroup parent, int i) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.clublist_layout, parent, false);
        return new ClubHolder(v);
    }

    class ClubHolder extends RecyclerView.ViewHolder {

        TextView lblName;
        Button btnDetails;

        public ClubHolder(@NonNull View itemView) {
            super(itemView);

            lblName = itemView.findViewById(R.id.lblName);
            btnDetails = itemView.findViewById(R.id.btnDetails);
        }
    }
}

我一直在该行收到一个错误Intent i = new Intent(context, ViewSingleClub.class);我认为这可能是一些与我的上下文变量引用本身，还不能确定，如果我得到正确的ID。有人能帮忙吗？

这是我的错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.marykate.marykatefordefyp, PID: 2718
    java.lang.NullPointerException
        at android.content.ComponentName.<init>(ComponentName.java:77)
        at android.content.Intent.<init>(Intent.java:3842)
        at com.example.marykate.marykatefordefyp.ClubAdapter1$1.onClick(ClubAdapter1.java:36)
        at android.view.View.performClick(View.java:4457)
        at android.view.View$PerformClick.run(View.java:18491)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5336)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:681)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

这是因为你被分配“与自身语境”。在那里你初始化适配器通过从阶级背景。

假设我有名字“ClubAdapter”并调用类名为“ClubClass”适配器

在ClubClass：

ClubAdapter clubAdapter = new ClubAdapter(list, context);
// if you'r calling it from activity then pass "Activity.this" and if fragment then "getContext()" as context.

and in ClubAdapter

public class ClubAdapter extends RecyclerView.Adapter<ClubAdapter.ClubHolder> {
    private Context context;
    private List<String> list;
   

    public ClubAdapter(List<String> list, Context context) {
        this.list = list;
        this.context = context;
    }
    
    @NonNull
    @Override
    public ClubHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View itemView = LayoutInflater.from(viewGroup.getContext())
                .inflate(R.layout.item_sample, viewGroup, false);
        return new ClubHolder(itemView, context);
    }
    
    
    public class ClubHolder extends RecyclerView.ViewHolder {

        private Context context;

        private ClunHolder(@NonNull View itemView,Context context) {
            super(itemView);
            this.context = context;
           
        }
        }
}

或者你可以让界面这个样子。

public interface RecycleViewOnItemClickListener {
    void onItemClick(int position);
}

并且它可以通过调用类传递到您的适配器。

假设我有名字“查看SampleAdapter”并命名为“SampleClass”在调用级接口“SampleClass”你可以通过适配器接口作为参数。

SampleAdapter sampleAdapter = new SampleAdapter(list, new RecycleViewOnItemClickListener() {
            @Override
            public void onItemClick(int position) {
                // do what you want to perform
            }
        });

在“ClubAdapter”

public class ClubAdapter extends RecyclerView.Adapter<ClubAdapter.ClubHolder> {
        private RecycleViewOnItemClickListener recycleViewOnItemClickListener;
        private List<String> list;
       

        public ClubAdapter(List<String> list, RecycleViewOnItemClickListener recycleViewOnItemClickListener) {
            this.list = list;
            this.recycleViewOnItemClickListener = recycleViewOnItemClickListener;
        }
        
        @NonNull
        @Override
        public ClubHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
            View itemView = LayoutInflater.from(viewGroup.getContext())
                    .inflate(R.layout.item_sample, viewGroup, false);
            return new ClubHolder(itemView, recycleViewOnItemClickListener);
        }
        
        
        public class ClubHolder extends RecyclerView.ViewHolder {

            private RecycleViewOnItemClickListener recycleViewOnItemClickListener;

            private ClunHolder(@NonNull View itemView,RecycleViewOnItemClickListener recycleViewOnItemClickListener) {
                super(itemView);
                this.recycleViewOnItemClickListener = recycleViewOnItemClickListener;
               //you can callback onItemClick method from here on button click event so it give callback in "ClubActivity".
               btn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    recycleViewOnItemClickListener.onItemClick(getAdapterPosition());
                }
            });
            }
            }
            }

Answer 2

为了解决这个问题，移动的这样onBindViewHolder()方法中下面几行代码：

holder.btnDetails.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent i = new Intent(context, ViewSingleClub.class);
        i.putExtra("id", clubId);
        context.startActivity(i);
    }
});

你看，我增加了点击监听器holder.btnDetails。

编辑：

根据您的意见，也请进行以下操作。更改构造函数：

public ClubAdapter1(@NonNull FirestoreRecyclerOptions<Club> options, Context context) {
    super(options);
    this.context = context;
}

当你创建的活动中您的适配器类的对象，也通过context给构造函数。