ListView用例

ListView 使用思路

在要使用的 layoutview 中添加 ListView 控件
如果子视图复杂，则写一个 itemView 的 layout 界面
封装数据对象 DataBean
实现合适的 Adapter
实例化 ListView 对象，拿到数据集，设置 Adapter

ListView 三层代码优化

ListView 的代码优化主要是 getView() 方法中对 view 的复用

不优化

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        TestBean testBean = arrayList.get(position);
        View view = LayoutInflater.from(mContext).inflate(resourceId,parent,false);
        ImageView imgHead = view.findViewById(R.id.iv_head);
        TextView tvContent = view.findViewById(R.id.tv_content);
        imgHead.setImageResource(testBean.getImgId());
        tvContent.setText(testBean.getName());
        return view;
    }

利用 convertView 缓存参数，复用布局

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        TestBean testBean = arrayList.get(position);
        View view
        if(convertView !=null){
            view = convertView;
        }else {
            view = LayoutInflater.from(mContext).inflate(resourceId,parent,false);
        }
        ImageView imgHead = view.findViewById(R.id.iv_head);
        TextView tvContent = view.findViewById(R.id.tv_content);
        imgHead.setImageResource(testBean.getImgId());
        tvContent.setText(testBean.getName());
        return view;
    }

不仅复用布局，而且通过增加 ViewHolder 复用控件的实例

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        TestBean testBean = arrayList.get(position);
        View view;
        ViewHolder viewHolder;
        if(convertView !=null){
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }else {
            view = LayoutInflater.from(mContext).inflate(resourceId,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.imgView = view.findViewById(R.id.iv_head);
            viewHolder.textView = view.findViewById(R.id.tv_content);
            view.setTag(viewHolder);// 将 viewHolder 存储在 view 中
        }
        viewHolder.imgView.setImageResource(testBean.getImgId());
        viewHolder.textView.setText(testBean.getName());
        return view;
    }

代码效果图

这就是效果图

ListView 代码实现

MainActivity.java

package com.demo.thorn.listviewdemo;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {

    private int count = 1;
    private ListView mListView;
    private int imgs[] = {R.drawable.img1,R.drawable.img2,R.drawable.img3
            ,R.drawable.img4,R.drawable.img5,R.drawable.img6
            ,R.drawable.img7,R.drawable.img8,R.drawable.img9,R.drawable.img10};;
    private ArrayList<TestBean> arrayList;

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

    private void initView() {
        mListView = findViewById(R.id.lv_show);
        arrayList = new ArrayList<>();
    }

    private void initData() {
        for(int i = 0;i<10;i++){
            TestBean testBean = new TestBean();
            testBean.setImgId(imgs[i]);
            testBean.setName("Content Here"+i);
            arrayList.add(testBean);
        }
        mListView.setAdapter(new MyListViewAdapter(this,R.layout.item_show,arrayList));
        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
            TestBean testBean = arrayList.get(i);
            Log.i("jin",testBean.getName());
        }
    });
    }
}

TestBean.java

package com.demo.thorn.listviewdemo;

public class TestBean {
    private int imgId;
    private  String name;

    public int getImgId() {
        return imgId;
    }

    public void setImgId(int imgId) {
        this.imgId = imgId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

MyListViewAdapter.java

package com.demo.thorn.listviewdemo;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;

public class MyListViewAdapter extends ArrayAdapter<TestBean> {

    ArrayList<TestBean> arrayList;
    int resourceId;
    Context mContext;

    public MyListViewAdapter(@NonNull Context context, int resource, @NonNull List<TestBean> objects) {
        super(context, resource, objects);
        resourceId = resource;
        arrayList = (ArrayList<TestBean>) objects;
        mContext = context;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        TestBean testBean = arrayList.get(position);
        View view;
        ViewHolder viewHolder;
        if(convertView !=null){
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }else {
            view = LayoutInflater.from(mContext).inflate(resourceId,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.imgView = view.findViewById(R.id.iv_head);
            viewHolder.textView = view.findViewById(R.id.tv_content);
            view.setTag(viewHolder);// 将 viewHolder 存储在 view 中
        }
        viewHolder.imgView.setImageResource(testBean.getImgId());
        viewHolder.textView.setText(testBean.getName());
        return view;
    }
}

layout_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.demo.thorn.listviewdemo.MainActivity">

<ListView
    android:id="@+id/lv_show"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

</RelativeLayout>

item_show.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:padding="10dp">

    <ImageView
        android:id="@+id/iv_head"
        android:layout_width="100dp"
        android:layout_height="100dp" />

    <TextView
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="20dp"
        android:id="@+id/tv_content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

ListView 使用思路

ListView 三层代码优化

代码效果图

ListView 代码实现

猜你喜欢