簡析Map及Map集合的遍歷解析、排序
阿新 • • 發佈：2019-01-09
先上效果圖：
（效果圖中的資料皆來自Map）
扯點犢子：
其實Android對Java基礎的要求並不高，雖然Android是基於Java的，但是Android有更多它自己的東西。
但是對於Java基礎還是需要充分的瞭解，這會對你的開發事半功倍，就像英語不好的開發者一樣可以看懂程式碼，但是英語好的開發者效率一定比英語不好的高。
一、Map
Map是以鍵值對的方式進行資料讀寫且無序，底層是通過key的hashCode計算hash值，根據hash值得到位置索引， 然後對該位置索引進行讀寫。
HashMap
HashMap是基於雜湊表的Map介面的非同步實現。此實現提供所有可選的對映操作，並允許使用null值和null鍵。
HashMap底層就是一個數組結構，陣列中的每一項又是一個連結串列。
二、實戰
1.資料來源
//新增資料 map1 = new HashMap<>(); map1.put(100, 10); map1.put(300, 30); map1.put(200, 20); map1.put(400, 40); ArrayList<String> list = new ArrayList<>(); for (int i = 0; i < 2; i++) { list.add(" ParseMap " + i); } map2 = new HashMap<>(); map2.put(100, list); map2.put(200, list); map2.put(300, list);
2.遍歷並排序
a）效果圖一。
b）效果圖二。//把key轉為一個集合 List<Integer> list = new ArrayList<>(map1.keySet()); //比較器 Collections.sort(list, new Comparator<Integer>() { @Override public int compare(Integer s1, Integer s2) { //升序排列 ，降序 把s1 s2調換即可 return s1.compareTo(s2); } }); //遍歷得到key和value，新增到集合 keyList = new ArrayList<>(); valueList = new ArrayList<>(); //遍歷map的常用方法一 for (Integer i : list) { Log.i("常用方法一", "key = " + i + " , value = " + map1.get(i)); keyList.add(i); valueList.add(map1.get(i)); }
第二種方法沒有排序，效果圖二中是300、200、100，而資料來源新增的順序是100、200、300，但是顯示的效果卻是相反的，這是因為Entry是從前向後新增的，也就是最後新增的資料在陣列的最前面。
//遍歷得到key和value，新增到集合
keyList = new ArrayList<>();
valueList = new ArrayList<>();
//遍歷map的常用方法二
for (Map.Entry<Integer, List<String>> entry : map2.entrySet()) {
Log.i("常用方法二", "key = " + entry.getKey() + " , value = " + entry.getValue());
keyList.add(entry.getKey());
valueList.add(entry.getValue());
}activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.yechaoa.parsemap.MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="@+id/button1"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="解析map並排序" />
<Button
android:id="@+id/button2"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="解析巢狀map" />
</LinearLayout>
<GridView
android:id="@+id/gridView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:columnWidth="90dp"
android:horizontalSpacing="10dp"
android:numColumns="2"
android:scrollbars="none"
android:stretchMode="columnWidth"
android:verticalSpacing="10dp"
android:visibility="gone" />
<ListView
android:id="@+id/listView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="10dp"
android:visibility="gone" />
</LinearLayout>
package com.yechaoa.parsemap;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private Button button1;
private Button button2;
private GridView gridView;
private ListView listView;
private HashMap<Integer, Integer> map1;
private HashMap<Integer, List<String>> map2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initData();
initListener();
}
private void initView() {
button1 = (Button) findViewById(R.id.button1);
button2 = (Button) findViewById(R.id.button2);
gridView = (GridView) findViewById(R.id.gridView);
listView = (ListView) findViewById(R.id.listView);
}
private void initData() {
//新增資料
map1 = new HashMap<>();
map1.put(100, 10);
map1.put(300, 30);
map1.put(200, 20);
map1.put(400, 40);
ArrayList<String> list = new ArrayList<>();
for (int i = 0; i < 2; i++) {
list.add(" ParseMap " + i);
}
map2 = new HashMap<>();
map2.put(100, list);
map2.put(200, list);
map2.put(300, list);
}
private void initListener() {
button1.setOnClickListener(this);
button2.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
//為演示效果直接控制樣式
case R.id.button1:
button2.setTextColor(Color.BLACK);
button1.setTextColor(Color.RED);
listView.setVisibility(View.GONE);
gridView.setVisibility(View.VISIBLE);
gridView.setAdapter(new GridViewAdapter(this, map1));
break;
case R.id.button2:
button1.setTextColor(Color.BLACK);
button2.setTextColor(Color.RED);
gridView.setVisibility(View.GONE);
listView.setVisibility(View.VISIBLE);
listView.setAdapter(new ListViewAdapter(this, map2));
break;
}
}
}
GridViewAdapter.java
package com.yechaoa.parsemap;
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.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
/**
* Created by yechao on 2017/4/21.
* Describe :
*/
public class GridViewAdapter extends BaseAdapter {
private Context mContext;
private Map<Integer, Integer> map1;
private final List<Integer> keyList;
private final List<Integer> valueList;
public GridViewAdapter(Context mContext, Map<Integer, Integer> map1) {
super();
this.mContext = mContext;
this.map1 = map1;
//把key轉為一個集合
List<Integer> list = new ArrayList<>(map1.keySet());
//比較器
Collections.sort(list, new Comparator<Integer>() {
@Override
public int compare(Integer s1, Integer s2) {
//升序排列 ，降序 把s1 s2調換即可
return s1.compareTo(s2);
}
});
//遍歷得到key和value，新增到集合
keyList = new ArrayList<>();
valueList = new ArrayList<>();
//遍歷map的常用方法一
for (Integer i : list) {
Log.i("常用方法一", "key = " + i + " , value = " + map1.get(i));
keyList.add(i);
valueList.add(map1.get(i));
}
}
@Override
public int getCount() {
return map1.size();
}
@Override
public Object getItem(int position) {
return map1.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = LayoutInflater.from(this.mContext).inflate(R.layout.item_gridview, parent, false);
holder = new ViewHolder();
holder.item_gv_textView1 = (TextView) convertView.findViewById(R.id.item_gv_textView1);
holder.item_gv_textView2 = (TextView) convertView.findViewById(R.id.item_gv_textView2);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.item_gv_textView1.setText(String.valueOf("充￥" + keyList.get(position)));
holder.item_gv_textView2.setText(String.valueOf("送￥" + valueList.get(position)));
return convertView;
}
private class ViewHolder {
TextView item_gv_textView1;
TextView item_gv_textView2;
}
}
ListViewAdapter.java
package com.yechaoa.parsemap;
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.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* Created by yechao on 2017/4/21.
* Describe :
*/
public class ListViewAdapter extends BaseAdapter {
private Context mContext;
private HashMap<Integer, List<String>> map2;
private List<Integer> keyList;
private List<List<String>> valueList;
public ListViewAdapter(Context mContext, HashMap<Integer, List<String>> map2) {
super();
this.mContext = mContext;
this.map2 = map2;
//遍歷得到key和value，新增到集合
keyList = new ArrayList<>();
valueList = new ArrayList<>();
//遍歷map的常用方法二
for (Map.Entry<Integer, List<String>> entry : map2.entrySet()) {
Log.i("常用方法二", "key = " + entry.getKey() + " , value = " + entry.getValue());
keyList.add(entry.getKey());
valueList.add(entry.getValue());
}
}
@Override
public int getCount() {
return map2.size();
}
@Override
public Object getItem(int position) {
return map2.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = LayoutInflater.from(this.mContext).inflate(R.layout.item_listview, parent, false);
holder = new ViewHolder();
holder.itemLvTitle = (TextView) convertView.findViewById(R.id.item_lv_title);
holder.itemLvListView = (MyListView) convertView.findViewById(R.id.item_lv_listView);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.itemLvTitle.setText(String.valueOf(keyList.get(position)));
//再把value集合傳給巢狀的ListViewSubAdapter
holder.itemLvListView.setAdapter(new ListViewSubAdapter(mContext, valueList.get(position)));
return convertView;
}
private class ViewHolder {
TextView itemLvTitle;
MyListView itemLvListView;
}
}