[Android Studio 30天自我挑战] RecyclerView元件介绍

这篇RecyclerView与前几篇介绍ListView相似，主要是用清单条列出来，让使用者简单明了，
RecyclerView是Google在Android5.0时推出，目的是优化ListView相关程序及效能。

今天这篇利用RecyclerView来做一个范例
要利用RecyclerView要先在Gradle Scripts/build.grade(.app)里的dependencies新增

implementation 'androidx.recyclerview:recyclerview:1.1.0'

接着在activity_main.xml里新增recyclerView元件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycleView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>

接着新增recyclerView要显示的排版xml档

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <ImageView
                android:id="@+id/myImageView"
                android:layout_width="100dp"
                android:layout_height="100dp"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/ic_launcher_background"
                tools:ignore="VectorDrawableCompat" />

            <TextView
                android:id="@+id/myText1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="24dp"
                android:layout_marginLeft="24dp"
                android:layout_marginTop="16dp"
                android:text="Title"
                android:textSize="24sp"
                android:textStyle="bold"
                app:layout_constraintStart_toEndOf="@+id/myImageView"
                app:layout_constraintTop_toTopOf="parent" />

            <TextView
                android:id="@+id/myText2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="24dp"
                android:layout_marginLeft="24dp"
                android:text="Description"
                android:textSize="16sp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintStart_toEndOf="@+id/myImageView"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.813" />
        </androidx.constraintlayout.widget.ConstraintLayout>

    </androidx.cardview.widget.CardView>
</androidx.constraintlayout.widget.ConstraintLayout>

排版设定好可以透过values/strings来设定要显示的文字

<resources>
    <string name="app_name">Recycleview</string>
    
    <string-array name="progrmming_languages">
        <item>可丽露</item>
        <item>舒芙蕾</item>
        <item>玛德莲</item>
        <item>马卡龙</item>
        <item>泡芙</item>
    </string-array>
    
    <string-array name="description">
        <item>是一种小型的法式甜点，表层则是硬脆\n又厚实的褐色焦糖外壳，内部是半融化\n状的蛋糕糊，散发着酒香和香草味。</item>
        <item>是一种源自法国的甜品，经烘焙後质感\n轻而蓬松</item>
        <item>是一种传统的贝壳形状的小蛋糕，来自\n於法国东北部洛林大区的两个市镇科梅\n尔西和利韦尔丹</item>
        <item>是一种用色彩缤纷绚丽的法国甜品，外\n壳坚硬但易碎，内陷黏稠扎实</item>
        <item>是一种源自法国的球形糕点，蓬松张孔\n的面皮中包裹鲜奶油、巧克力乃至冰淇\n淋</item>
    </string-array>
</resources>

接着建立Adapter来控管每个item的显示设定，我们自订了一个名为MyAdapter的类别，此类别继承了 RecyclerView.Adapter

package com.example.recycleview;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

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

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    String data1[],data2[];
    int images[];
    Context context;
    public MyAdapter(Context ct,String s1[],String s2[],int img[]){
        context = ct;
        data1 = s1;
        data2 = s2;
        images = img;
    }
    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.my_row,parent,false);
        return new MyViewHolder(view);
    }
    @Override
    //透过 position 参数指定每个item所用到的资料
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        holder.myText1.setText(data1[position]);
        holder.myText2.setText(data2[position]);
        holder.myImage.setImageResource(images[position]);
    }
    @Override
    public int getItemCount() {
        return images.length;
    }
    public class MyViewHolder extends RecyclerView.ViewHolder{
        TextView myText1,myText2;
        ImageView myImage;
        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            myText1 = itemView.findViewById(R.id.myText1);
            myText2 = itemView.findViewById(R.id.myText2);
            myImage = itemView.findViewById(R.id.myImageView);
        }
    }
}

设定完Adapter後就可以在MainActivity.java中设定RecyclerView

package com.example.recycleview;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
    RecyclerView recycleView;


    String s1[] ,s2[];
    int images[] = {R.drawable.coco,R.drawable.su,R.drawable.lan,R.drawable.mar,R.drawable.pabu};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recycleView = findViewById(R.id.recycleView);
        s1 = getResources().getStringArray(R.array.progrmming_languages);
        s2 = getResources().getStringArray(R.array.description);

        MyAdapter myAdapter = new MyAdapter(this,s1,s2,images);
        recycleView.setAdapter(myAdapter);
        recycleView.setLayoutManager(new LinearLayoutManager(this));
    }
}

这样就完成罗