网站开发用例说明/软文推广案例500字

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"><ListViewandroid: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"><TextViewandroid: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<>();@Overrideprotected 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() {@Overridepublic 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;}@Overridepublic int getCount() {return data.size();}@Overridepublic Object getItem(int i) {return null;}@Overridepublic long getItemId(int i) {return i;}@Overridepublic 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;}@Overridepublic int getCount() {return data.size();}@Overridepublic Object getItem(int i) {return null;}@Overridepublic long getItemId(int i) {return i;}@Overridepublic 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;}
}