如何在 RecyclerView Java 中创建 OnClick 事件

Question

我在尝试在我的 CategoriesAdapter.Java 中创建 OnClickListener 时遇到问题

我正在尝试做的事情的简短摘要：我正在尝试构建应用程序的一部分，以显示某些业务类型的“类别”，即技术、金融等

我想确保用户能够点击一个类别并基本上将他们带到所需的类别； "用户点击'财务'用户转到'财务'类别。

如果你能帮助我，我会把我的代码贴在这里。

CategoriesAdapter.Java

package com.example.tencil.HelperClasses.HomeAdapter;


import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.tencil.R;
import com.example.tencil.User.CategoriesHelperClass;



import java.util.ArrayList;

import static android.content.ContentValues.TAG;

public class CategoriesAdapter extends RecyclerView.Adapter<CategoriesAdapter.ViewHolder> {

ArrayList<CategoriesHelperClass> categories;
private ArrayList<CategoriesHelperClass> mTitle = new ArrayList<>();
private ArrayList<CategoriesHelperClass> mImages = new ArrayList<>();
private android.content.Context mcontext;



public CategoriesAdapter(ArrayList<CategoriesHelperClass> categories) {
    this.categories = categories;
    this.mTitle = mTitle;
    this.mImages = mImages;
    this.mcontext = mcontext;
}



//Returns Categories View Dynamically
public ViewHolder onCreateViewHolder( ViewGroup parent, int viewType) {
    View view = LayoutInflater.from ( parent.getContext () ).inflate ( R.layout.categories_card_design, parent, false );
    ViewHolder holder = new ViewHolder ( view );
    return new ViewHolder ( view );
}

public void onBindViewHolder( ViewHolder holder, int position) {

    Log.d (TAG, "OnBindViewHolder: Called.");
    holder.image.setImageResource ( com.example.tencil.HelperClasses.HomeAdapter.CategoriesHelperClass.getImage () );
    holder.title.setText ( com.example.tencil.HelperClasses.HomeAdapter.CategoriesHelperClass.getTitle () );
    holder.parentLayout.setOnClickListener ( new View.OnClickListener () {

        public void onClick(View v) {
            Log.d (TAG, "OnClick: Clicked on" + mImages.get ( position ));
            Toast.makeText ( mcontext, (CharSequence) mTitle.get ( position ), Toast.LENGTH_SHORT ).show ();
        }
    } );


}

public int getItemCount() {

    return categories.size ();
}

//HOLDS VIEWS
public static class ViewHolder extends RecyclerView.ViewHolder {
    ImageView image;
    TextView title;
    RelativeLayout parentLayout;

    public ViewHolder(View itemView) {
        super ( itemView );


        //HOOKS
        image = itemView.findViewById ( R.id.categories_image );
        title = itemView.findViewById ( R.id.categories_title );
        parentLayout = itemView.findViewById ( R.id.parentLayout );



    }

    }
}

UserDashboard.XML

<?xml version="1.0" encoding="utf-8"?>

<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimary"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    tools:context=".User.UserDashboard">


    <com.google.android.material.navigation.NavigationView
        android:id="@+id/navigation_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:background="#fff"
        android:theme="@style/navigationTheme"
        app:headerLayout="@layout/menu_header"
        app:menu="@menu/main_menu" />

    <LinearLayout
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/lightWhite"
        android:orientation="vertical">

        <RelativeLayout

            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:background="@color/colorPrimary"
            android:padding="20dp">


            <ImageView
                android:id="@+id/menu_icon"
                android:layout_width="40dp"
                android:layout_height="40dp"
                android:src="@drawable/menu_icon" />


        </RelativeLayout>

        <ScrollView
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="#fff"
                android:orientation="vertical">

                <RelativeLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content">

                    <TextView
                        android:id="@+id/app_name"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_centerHorizontal="true"
                        android:fontFamily="@font/raleway_bold"
                        android:paddingTop="8dp"
                        android:text="@string/tencil"
                        android:textColor="@color/colorAccent"
                        android:textSize="28sp" />


                </RelativeLayout>

                <LinearLayout
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:orientation="horizontal"
                    android:paddingTop="20dp">

                    <LinearLayout
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:orientation="vertical">

                        <RelativeLayout
                            android:id="@+id/card_1"
                            android:layout_width="60dp"
                            android:layout_height="60dp"
                            android:layout_margin="10dp"
                            android:background="@drawable/card_3"
                            android:elevation="8dp"
                            android:onClick="cardClicked1">

                            <ImageView
                                android:layout_width="30dp"
                                android:layout_height="30dp"
                                android:layout_centerInParent="true"
                                android:src="@drawable/tencilw" />

                        </RelativeLayout>

                        <TextView
                            android:layout_width="match_parent"
                            android:layout_height="50dp"
                            android:text="@string/socialmedis"
                            android:textAlignment="center" />


                    </LinearLayout>

                    <LinearLayout
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:orientation="vertical">

                        <RelativeLayout
                            android:id="@+id/card_2"
                            android:layout_width="60dp"
                            android:layout_height="60dp"
                            android:layout_margin="10dp"
                            android:background="@drawable/card_1"
                            android:elevation="8dp"
                            android:onClick="cardClicked2">>

                            <ImageView
                                android:layout_width="30dp"
                                android:layout_height="30dp"
                                android:layout_centerInParent="true"
                                android:src="@drawable/piggy" />

                        </RelativeLayout>

                        <TextView
                            android:layout_width="match_parent"
                            android:layout_height="40dp"
                            android:text="@string/finance"
                            android:textAlignment="center" />


                    </LinearLayout>

                    <LinearLayout
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:orientation="vertical">

                        <RelativeLayout
                            android:id="@+id/card_3"
                            android:layout_width="60dp"
                            android:layout_height="60dp"
                            android:layout_margin="10dp"
                            android:background="@drawable/card_2"
                            android:elevation="8dp"
                            android:onClick="cardClicked3">

                            <ImageView
                                android:layout_width="50dp"
                                android:layout_height="50dp"
                                android:layout_centerInParent="true"
                                android:src="@drawable/pws" />

                        </RelativeLayout>

                        <TextView
                            android:layout_width="match_parent"
                            android:layout_height="40dp"
                            android:text="@string/tech"
                            android:textAlignment="center" />


                    </LinearLayout>

                    <LinearLayout
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:orientation="vertical">

                        <RelativeLayout
                            android:id="@+id/card_4"
                            android:layout_width="60dp"
                            android:layout_height="60dp"
                            android:layout_margin="10dp"
                            android:background="@drawable/card_4"
                            android:elevation="8dp"
                            android:onClick="cardClicked4">

                            <ImageView
                                android:layout_width="30dp"
                                android:layout_height="30dp"
                                android:layout_centerInParent="true"
                                android:src="@drawable/analysisw" />

                        </RelativeLayout>

                        <TextView
                            android:layout_width="match_parent"
                            android:layout_height="40dp"
                            android:text="@string/fintech"
                            android:textAlignment="center" />


                    </LinearLayout>


                </LinearLayout>

                <RelativeLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginTop="20dp"
                    android:background="@drawable/banner_background">

                    <LinearLayout
                        android:id="@+id/featured_background"
                        android:layout_width="170dp"
                        android:layout_height="280dp"
                        android:layout_margin="10dp"
                        android:background="@drawable/banner_background"
                        android:orientation="vertical">

                        <TextView
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:layout_marginLeft="10dp"
                            android:layout_marginTop="50dp"
                            android:text="@string/featured_companies"
                            android:textAllCaps="true"
                            android:textColor="#000"
                            android:textSize="25dp" />


                        <TextView
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:layout_margin="10dp"
                            android:text="@string/featured_companies_description" />


                    </LinearLayout>

                    <androidx.recyclerview.widget.RecyclerView
                        android:id="@+id/featured_recycler"
                        android:layout_width="match_parent"
                        android:layout_height="300dp"
                        android:layout_marginStart="10dp"
                        android:layout_toEndOf="@+id/featured_background"
                        android:background="#fff" />


                </RelativeLayout>


                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="20dp"
                    android:orientation="vertical"
                    android:padding="20dp">

                    <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content">

                        <TextView
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:fontFamily="@font/raleway_bold"
                            android:text="@string/categories"
                            android:textAllCaps="true"
                            android:textColor="#000"
                            android:textSize="20sp" />

                        <TextView
                            android:id="@+id/view_all"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:layout_alignParentRight="true"
                            android:layout_centerVertical="true"
                            android:onClick="viewAllClicked"
                            android:text="@string/view_all" />


                    </RelativeLayout>


                    <androidx.recyclerview.widget.RecyclerView
                        android:layout_width="match_parent"
                        android:id="@+id/parentLayout"
                        android:layout_height="150dp" />



                </LinearLayout>


            </LinearLayout>
        </ScrollView>


    </LinearLayout>


</androidx.drawerlayout.widget.DrawerLayout>

CategoriesHelperClass.java

    package com.example.tencil.HelperClasses.HomeAdapter;

public class CategoriesHelperClass {
    static int image;
    static String title;

    //SETTER
    public CategoriesHelperClass(int image, String title) {
        this.image = image;
        this.title = title;
    }

    //GETTER
    public static int getImage() {
        return image;
    }

    public static String getTitle() {
        return title;
    }


}

控制台错误消息

    E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.tencil, PID: 5226
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.tencil.HelperClasses.HomeAdapter.CategoriesAdapter.onBindViewHolder(CategoriesAdapter.java:55)
    at com.example.tencil.HelperClasses.HomeAdapter.CategoriesAdapter.onBindViewHolder(CategoriesAdapter.java:25)

任何帮助将不胜感激这已经困扰了我几个小时。

Answer 1

这就是你在 kotlin 中使用回调解决这个问题的方法，在 java 中你需要使用监听器

在你的Activity/Fragment 中有一个函数可以处理这样的导航

请注意，下面的代码就像一个伪代码，您必须进行相应的调整

private fun navigateTo(title: String) {
    //handle navigation with the title normally here
    val intent = Intent(this, Category::class.java)
    intent.putExtra("Title", title)
    startActivity(intent)
}

在您的 Activity 的 onCreate 中

val categoriesAdapter = CategoriesAdapter({ title ->
        navigateTo(title)
    })

这是 Adapter 和 ViewHolder 类

private class CategoriesAdapter(val callBack:(String)-> Unit){
    override fun onCreateViewHolder(): CategoriesViewHolder{
        return CategoriesViewHolder(callBack)
    }
}

private class CategoriesViewHolder(val callBack: (String) -> Unit){
    fun bind(){
        item.setOnClickListener{
            callBack(title)
        }
    }
}

当您单击某个项目时，您将从视图持有者的 bind 方法中获取标题和任何您想要的详细信息，该方法在任何给定时间仅包含 1 个单个项目，并且将运行该方法命名为callBack 并将其标题发送回适配器，适配器什么也不做，只是再次调用相同的方法并在Activity 中为其发送标题，然后您的Activity 将运行navigateTo 方法并执行所需的操作。

在 java 中，您将在您的 Activity/Fragment 中创建一个 Listener，如果我没记错的话，您将直接从您的 ViewHolder 中使用它，这将产生相同的效果

Answer 2

在java中，你必须将view的每个元素转换成它的类，findViewById()返回T类的成员，所以你会得到普通的View而不是ImageView、TextView等。

public static class ViewHolder extends RecyclerView.ViewHolder {
    ImageView image;
    TextView title;
    RelativeLayout parentLayout;
    
    public ViewHolder(View itemView) {
        super ( itemView );
        //HOOKS
        image = (ImageView) itemView.findViewById ( R.id.categories_image );
        title = (TextView) itemView.findViewById ( R.id.categories_title );
        parentLayout = (RelativeLayout) itemView.findViewById ( R.id.parentLayout );
    }
}

另外，如果你想点击整行，你应该使用holder.itemView.setOnClickListener()。仅当您触摸行视图中的可用空间时，在 RelativeLayout 上调用单击侦听器才会起作用，因此它可能不会每次都起作用。

Answer 3

从列表中获取数据并设置为视图（在 onBindViewHolder 方法中）

        CategoriesHelperClass item = categories.get(position);

        holder.image.setImageResource ( item.getImage () );
        holder.title.setText ( item.getTitle () );
        holder.itemView.setOnClickListener ( new View.OnClickListener () {

            public void onClick(View v) {
                Log.d (TAG, "OnClick: Clicked on" + mImages.get ( position ));
                Toast.makeText ( mcontext, item.getTitle (), Toast.LENGTH_SHORT ).show ();
            }
        } );

这两个列表不需要，你可以用类别列表处理图像和图像

private ArrayList<CategoriesHelperClass> mTitle = new ArrayList<>();
private ArrayList<CategoriesHelperClass> mImages = new ArrayList<>();