ListView

效果图

1、在activity_main.xml中创建ListView，再创建list_item.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="vertical">
 
    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
    
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="30sp"/>
 
</LinearLayout>

2、MainActivity.java

package com.example.myapplication;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import androidx.appcompat.app.AppCompatActivity;
import java.util.ArrayList;
import java.util.List;
 
public class MainActivity extends AppCompatActivity {
 
    private List<Bean> data = new ArrayList<>();
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
//       每个item显示的内容
        for (int i = 0; i < 100; i++) {
            Bean bean = new Bean();
            bean.setName("局长，我想进步了！" + i);
            data.add(bean);
        }
 
        ListView lv = findViewById(R.id.lv);
        lv.setAdapter(new MyAdapter(data, this));
        
//       触发item点击事件
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                Log.e("leo", "onItemClick" + i);
            }
        });
    }
}

3、创建Bean类

package com.example.myapplication;
 
public class Bean {
 
    String name;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
}

4、创建一个适配器MyAdapter

package com.example.myapplication;
 
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
 
import java.util.List;
 
public class MyAdapter extends BaseAdapter {
    private List<Bean> data;
    private Context context;
 
    public MyAdapter(List<Bean> data, Context context) {
        this.data = data;
        this.context = context;
    }
 
    @Override
    public int getCount() {
        return data.size();
    }
 
    @Override
    public Object getItem(int i) {
        return null;
    }
 
    @Override
    public long getItemId(int i) {
        return i;
    }
 
    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        if (view == null) {
            view = LayoutInflater.from(context).inflate(R.layout.list_item,viewGroup,false);
        }
        TextView textView = view.findViewById(R.id.tv);
        textView.setText(data.get(i).getName());
 
        Log.e("leo","getView" + i);
        return view;
    }
}

上述标红处需重点理解

5、使用ViewHolder优化适配器

降低findViewById的使用，提高运行速度

package com.example.myapplication;
 
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
 
import java.util.List;
 
public class MyAdapter extends BaseAdapter {
    private List<Bean> data;
    private Context context;
 
    public MyAdapter(List<Bean> data, Context context) {
        this.data = data;
        this.context = context;
    }
 
    @Override
    public int getCount() {
        return data.size();
    }
 
    @Override
    public Object getItem(int i) {
        return null;
    }
 
    @Override
    public long getItemId(int i) {
        return i;
    }
 
    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        ViewHolder viewHolder;
        if (view == null) {
            viewHolder = new ViewHolder();
            view = LayoutInflater.from(context).inflate(R.layout.list_item,viewGroup,false);
            viewHolder.textView = view.findViewById(R.id.tv);
            view.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) view.getTag();
        }
        
        viewHolder.textView.setText(data.get(i).getName());
 
        Log.e("leo","getView" + i);
        return view;
    }
 
    private final class ViewHolder {
        TextView textView;
    }
}