Android中BaseAdapter配合ListView的使用（解决分割线显示问题）

1.简介

ListView可显示垂直滚动的视图集合，其中每个视图紧邻列表中的上一个视图。xml的主要属性如下图，其中headerDividersEnabled和footerDividersEnabled属性在使用的时候有很多需要注意的地方（特别是headerDividersEnabled属性，不管你怎么搞，顶部的分割线都不会显示，我是真的搞了一下午，最后发现书的代码有点问题 ）。

设置分割线需要注意的地方。

1. 代码中的setDivider方法只能设置具体的图片，不能设置颜色，即使把颜色值转为ColorDrawable也不行。在布局文件中可对divider属性直接指定颜色值。
2. 代码中要设置分隔线，务必先调用setDivider方法再调用setDividerHeight方法。如果先调用setDividerHeight再调用setDivider，分隔线高度就会变成分隔图片的高度，而不是setDividerHeight设置的高度。如图一，正常应该是图二。
   
   
3. 想要显示底部的分割线，当前ListView的高度不能为wrap_content，否则就算把footerDividersEnabled设置为true、调用setFooterDividersEnabled方法设置为true，这条底部的分隔线也不会出现。除非把列表的高度设置为match_parent或设置足够高，才会显示底部的分隔线。
4. 顶部的分割线是根本不会显示的，不管怎么调（反正我没调出来）。
5. 显示底部和顶部分割线简单的方法应该就是使用padding+background了（不过还是有坑，具体看例子的注释）。

2.使用例子

下面这个例子基本上把设置分割线的方法都试了各遍，大家可以自己试试。新建ListViewDemoActivity，下面是代码、效果图和分割线图片。

1. item_list_view.xml。ListView的列表项的布局文件。

2. item_dropdown.xml。Spinner的列表项的布局文件。

3. item_selected.xml。Spinner选中时的布局文件，如图。
   

4. ItemDemo.java。ListView的Item代码文件。

package xyz.strasae.androidlearn.myandroidapplication.bean;

import java.util.ArrayList;

import xyz.strasae.androidlearn.myandroidapplication.R;

public class ItemDemo {
    private static int[] iconArray = {R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher
            , R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher};
    private static String[] nameArray = {"item1", "item2", "item3", "item4", "item5", "item6", "item 7"};
    private static String[] descriptionArray = {"This is item1's Description", "This is item2's Description", "This is item3's Description",
            "This is item4's Description", "This is item5's Description", "This is item6's Description", "This is item 7's Description"};

    public int image;
    public String name;
    public String description;

    public ItemDemo() {
        image = 0;
        name = "";
        description = "";
    }

    public ItemDemo(int image, String name, String description) {
        this.image = image;
        this.name = name;
        this.description = description;
    }

    public static ArrayList getDefaultList() {
        ArrayList arrayList = new ArrayList<>();
        for(int i = 0; i < iconArray.length; i++) {
            arrayList.add(new ItemDemo(iconArray[i], nameArray[i], descriptionArray[i]));
        }
        return arrayList;
    }
}

5. MyBaseAdapter.java。ListView的适配器，同时实现了AdapterView.OnItemClickListener和AdapterView.OnItemLongClickListener接口。

package xyz.strasae.androidlearn.myandroidapplication.adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;

import xyz.strasae.androidlearn.myandroidapplication.R;
import xyz.strasae.androidlearn.myandroidapplication.bean.ItemDemo;

public class MyBaseAdapter extends BaseAdapter implements AdapterView.OnItemClickListener, AdapterView.OnItemLongClickListener {
    private LayoutInflater layoutInflater;
    private Context context;
    private int layoutId;
    private int background;
    private ArrayList itemDemoArrayList;

    /**
     *
     * @param context 设备上下文
     * @param layoutId 列表项的视图id
     * @param itemDemoArrayList 数据
     * @param background 列表项的背景颜色
     */
    public MyBaseAdapter(Context context, int layoutId, ArrayList itemDemoArrayList, int background) {
        this.context = context;
        layoutInflater = LayoutInflater.from(this.context);
        this.itemDemoArrayList = itemDemoArrayList;
        this.background = background;
        this.layoutId = layoutId;
    }

    @Override
    public int getCount() {
        return itemDemoArrayList.size();
    }

    @Override
    public Object getItem(int i) {
        return itemDemoArrayList.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        if(convertView == null) {
            viewHolder = new ViewHolder();
            convertView = layoutInflater.inflate(layoutId, null);
            viewHolder.ll_item = convertView.findViewById(R.id.ll_item);
            viewHolder.iv_icon = convertView.findViewById(R.id.iv_icon);
            viewHolder.tv_name = convertView.findViewById(R.id.tv_name);
            viewHolder.tv_description = convertView.findViewById(R.id.tv_description);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        ItemDemo itemDemo = itemDemoArrayList.get(position);
        viewHolder.ll_item.setBackgroundColor(background);
        viewHolder.iv_icon.setImageResource(itemDemo.image);
        viewHolder.tv_name.setText(itemDemo.name);
        viewHolder.tv_description.setText(itemDemo.description);
        return convertView;
    }

    @Override
    public void onItemClick(AdapterView adapterView, View view, int i, long l) {
        Toast.makeText(context, "你选择的是" + itemDemoArrayList.get(i).name, Toast.LENGTH_SHORT).show();
    }

    @Override
    public boolean onItemLongClick(AdapterView adapterView, View view, int i, long l) {
        Toast.makeText(context, "你长按了" + itemDemoArrayList.get(i).name, Toast.LENGTH_SHORT).show();
        return true;
    }

    public final class ViewHolder {
        private LinearLayout ll_item;
        private ImageView iv_icon;
        private TextView tv_name;
        private TextView tv_description;
    }
}

6. activity_list_view_demo.xml。ListViewDemoActivity的布局文件。

7. ListViewDemoActivity.java。

package xyz.strasae.androidlearn.myandroidapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.Spinner;

import java.util.ArrayList;

import xyz.strasae.androidlearn.myandroidapplication.adapter.MyBaseAdapter;
import xyz.strasae.androidlearn.myandroidapplication.bean.ItemDemo;

public class ListViewDemoActivity extends AppCompatActivity {
    private ListView lv_demo;
    private ArrayList itemDemoArrayList;
    private Spinner sp_divider_type;
    private Drawable drawable;
    private int dividerHeight = 5;
    private String[] dividerArray = {
            "不显示分割线（分割线高度为0）",
            "不显示分割线（设置为null）",
            "只显示内部分割线（先设置分割线高度，再设置分割线图片）",
            "只显示内部分割线（先设置分割线图片，后设置分割线高度）",
            "显示底部分割线（ListView高度为wrap_content）",
            "显示底部分割线（ListView高度为match_parent）",
            "显示顶部分割线（其实显示不了）",
            "用padding显示全部分割线"
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_view_demo);
        lv_demo = findViewById(R.id.lv_demo);
        itemDemoArrayList = ItemDemo.getDefaultList();
        MyBaseAdapter myBaseAdapter = new MyBaseAdapter(ListViewDemoActivity.this, R.layout.item_list_view, itemDemoArrayList, Color.WHITE);
        lv_demo.setAdapter(myBaseAdapter);
        lv_demo.setOnItemClickListener(myBaseAdapter);
        lv_demo.setOnItemLongClickListener(myBaseAdapter);
        drawable = this.getResources().getDrawable(R.drawable.divider_red2, null);

        sp_divider_type = findViewById(R.id.sp_divider_type);
        ArrayAdapter arrayAdapter = new ArrayAdapter<>(ListViewDemoActivity.this, R.layout.item_selected, dividerArray);
        arrayAdapter.setDropDownViewResource(R.layout.item_dropdown);
        sp_divider_type.setPrompt("请选择分割线显示方式");
        sp_divider_type.setAdapter(arrayAdapter);
        sp_divider_type.setOnItemSelectedListener(new DividerSelectedListener());
        sp_divider_type.setSelection(0);
    }

    private class DividerSelectedListener implements AdapterView.OnItemSelectedListener {

        @Override
        //第二个参数代表选中的（0开始）
        public void onItemSelected(AdapterView adapterView, View view, int i, long l) {
            LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
            lv_demo.setDivider(drawable);
            lv_demo.setDividerHeight(dividerHeight);
            lv_demo.setPadding(0, 0, 0, 0);
            lv_demo.setBackgroundColor(Color.TRANSPARENT);
            if(i == 0) {
                lv_demo.setDividerHeight(0);
            } else if(i == 1) {
                lv_demo.setDivider(null);
                lv_demo.setDividerHeight(dividerHeight);
            } else if(i == 2) {
                lv_demo.setDividerHeight(dividerHeight);
                lv_demo.setDivider(drawable);
            }else if(i == 3) {
                lv_demo.setDivider(drawable);
                lv_demo.setDividerHeight(dividerHeight);
            }else if(i == 4) {
                lv_demo.setFooterDividersEnabled(true);
            }else if(i == 5) {
                //第二个参数代表height 第三个参数代表权重
                layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 1);
                lv_demo.setFooterDividersEnabled(true);
            }else if(i == 6) {
                layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 1);
                lv_demo.setFooterDividersEnabled(true);
                lv_demo.setHeaderDividersEnabled(true);
            } else if(i == 7) {
            	//注意这里必须先把Divider设置为null padding+background才会有用
                lv_demo.setDivider(null);
                lv_demo.setDividerHeight(dividerHeight);
                lv_demo.setPadding(0, dividerHeight, 0, dividerHeight);
                lv_demo.setBackground(drawable);
            }
            lv_demo.setLayoutParams(layoutParams);
        }

        @Override
        public void onNothingSelected(AdapterView adapterView) {

        }
    }
}