Android學習之recycleview

recycleview可以說是listview（已經淘汰）的強化版，也是學完了listview纔來的recycleview。其有強制的四級緩存機制，強制要求開發者使用優化。

注意：item的高度在listview和recycleview，代表意義不同，因爲兩者加載方式不同的原因。前者item高度不會生效，會自動採用wrap_content，後者是item高度會生效，指定item多高就是多高（可以自己採用wrap_content或者自己設定指定高度）。（被自己蠢哭過，）

 

目錄

源碼

activity：

包裝類

layout

activity_main.xml

item_layout.xml

備註：

---

源碼

activity：

package com.example.myapplication3;

import androidx.annotation.DrawableRes;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    List<Chat> list = new ArrayList<>();

    RecyclerView mRecyclerView;

    String[] na = {"秋秋", "彭彭彭彭", "我又發現", "實驗教學準備兼職", "兼職文員", "此羣涉嫌違規禁止訪問",
            "京東JD.COM", "test", "test", "test", "test", "test"};
    String[] co = {"馬上看完了", "312", "http://ffm.qq.com", "學剛：新年快樂", "鹿訂記結賬小姐姐：[OK]",
            "徐一凡：[發呆]", "iPhone全場搶卷立減700元", "test", "test", "test", "test", "test"};
    String[] ti = {"13:00", "星期二", "2020/1/27", "2020/1/1", "2019/4/27", "13:06：", "13:01", "test",
            "test", "test", "test", "test"};


    int[] id = new int[100];


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

        mRecyclerView = findViewById(R.id.recyclerView);

        id[0] = (int) R.drawable.b;
        id[1] = (int) R.drawable.a1;
        id[2] = (int) R.drawable.a2;
        id[3] = (int) R.drawable.a3;
        id[4] = (int) R.drawable.b1;
        id[5] = (int) R.drawable.b3;
        id[6] = (int) R.drawable.b4;
        id[7] = (int) R.drawable.b4;
        id[8] = (int) R.drawable.b4;
        id[9] = (int) R.drawable.b4;
        id[10] = (int) R.drawable.b4;
        id[11] = (int) R.drawable.b4;

        for (int i = 0; i < 12; i++) {
            Chat chat = new Chat();
            chat.name = na[i];
            chat.content = co[i];
            chat.time = ti[i];
            chat.pic = id[i];
            list.add(chat);

        }
        mRecyclerView.setAdapter(new Myadapter());
        //
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
    }


    public class Myadapter extends RecyclerView.Adapter<MyRcycleviewhoder> {

        @NonNull
        @Override
        public MyRcycleviewhoder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
//        創建item，及其緩存類
            View view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_layout, parent, false);
            MyRcycleviewhoder myRcycleviewhoder = new MyRcycleviewhoder(view);
            return myRcycleviewhoder;
        }

        @Override
        public void onBindViewHolder(@NonNull MyRcycleviewhoder holder, int position) {
            Chat chat = list.get(position);

            holder.name.setText(chat.name);
            holder.content.setText(chat.content);
            holder.time.setText(chat.time);
            holder.pic.setImageDrawable(getResources().getDrawable((int) chat.pic));
        }

        @Override
        public int getItemCount() {
            return list.size();
        }
    }

    public class MyRcycleviewhoder extends RecyclerView.ViewHolder {//緩存處理4級

        public TextView name;
        public TextView content;
        public TextView time;
        public ImageView pic;

        public MyRcycleviewhoder(@NonNull View itemView) {

            super(itemView);//初始化模塊

            name = itemView.findViewById(R.id.name);
            content = itemView.findViewById(R.id.content);
            time = itemView.findViewById(R.id.time);
            pic = itemView.findViewById(R.id.pic);
        }
    }


}

包裝類

package com.example.myapplication3;

import java.util.Date;

public class Chat {
    public String name;
    public String content;
    public String time;
    public int pic;
}

layout

activity_main.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ededed"
    android:orientation="vertical"
    tools:context=".MainActivity">


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/imageView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView4"
        app:layout_constraintVertical_bias="0.5">

    </androidx.recyclerview.widget.RecyclerView>

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="72dp"
        android:layout_height="47dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ab" />

    <ImageButton
        android:id="@+id/imageButton"
        android:layout_width="57dp"
        android:layout_height="48dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ac" />

    <ImageView
        android:id="@+id/imageView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView2"
        app:srcCompat="@drawable/aa" />

    <ImageView
        android:id="@+id/imageView4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView3"
        app:srcCompat="@drawable/ad" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="409dp"
        android:layout_height="70dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:srcCompat="@drawable/q" />

</androidx.constraintlayout.widget.ConstraintLayout>

item_layout.xml

<?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:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/pic"
        android:layout_width="60dp"
        android:layout_height="60dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/a1" />

    <TextView
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:text="TextView"
        android:textSize="20sp"
        android:textStyle="bold"
        app:layout_constraintStart_toEndOf="@+id/pic"
        app:layout_constraintTop_toTopOf="@+id/pic" />

    <TextView
        android:id="@+id/content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        android:textSize="17sp"
        app:layout_constraintBottom_toBottomOf="@+id/pic"
        app:layout_constraintStart_toStartOf="@+id/name" />

    <TextView
        android:id="@+id/time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="21dp"
        android:layout_marginRight="21dp"
        android:text="TextView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="@+id/name" />
</androidx.constraintlayout.widget.ConstraintLayout>

備註：

至於drawable裏面的圖片資源就沒有弄上來了，這不是重點。