问题描述
我有一个列表，并linkedhashmap.I我在主类的顶部以下行定义：
列表＆LT;会话与GT; conversationsList =新的ArrayList＆LT;会话与GT;（）;
LinkedHashMap的＆LT;弦乐，会话与GT; conversationsMap =新的LinkedHashMap＆LT;弦乐，会话与GT;（）;
在的onCreate（）我从数据库将数据传输到HashMap的，然后转移映射值到ArrayList和我使用此ArrayList的适配器视图与下面几行：
conversationsMap = _db.getAllConversations（）;
conversationsList =新的ArrayList＆LT;会话与GT;（conversationsMap.values（））;
conversationsAdapter =新ConversationsAdapter（这一点，conversationsList）;
但有件事我不understand.I可以更新这些行名单：
conversationsMap.get（ROOM_NAME）.increaseUnread（）;
（（ConversationsAdapter）conversationsAdapter）.updateConversations（conversationsList）;
它的工作，但我没有更新 conversationsList 为什么这工作，我不明白？我刚刚更新 conversationsMap 不是 conversationsList 。任何人都可以，为什么这是工作向我解释？
在数据库处理程序 getAllConversations 方法：
公共LinkedHashMap的＆LT;弦乐，会话与GT; getAllConversations（）{
清单＆LT;会话与GT; conversationsList =新的ArrayList＆LT;会话与GT;（）;
最终的LinkedHashMap＆LT;弦乐，会话与GT;对话=新的LinkedHashMap＆LT;弦乐，会话与GT;（）;
字符串selectQuery =SELECT * FROM+ TABLE_CONVERSATIONS +ORDER BY ID ASC; SQLiteDatabase分贝= this.getWritableDatabase（）;
光标光标= db.rawQuery（selectQuery，NULL）;
如果（cursor.moveToFirst（））{
做{
交谈交谈=新的对话（）;
Conversation.setId（的Integer.parseInt（cursor.getString（0）））;
Conversation.setSender（cursor.getString（1））;
Conversation.setTo（cursor.getString（2））;
Conversation.setName（cursor.getString（3））;
Conversation.setBio（cursor.getString（4））;
Conversation.setPicture（cursor.getString（5））;
Conversation.setTime（的Integer.parseInt（cursor.getString（6）））;
Conversation.setUnread（的Integer.parseInt（cursor.getString（7）））;
conversations.put（cursor.getString（2），对话）;
}而（cursor.moveToNext（））;
}
cursor.close（）;
回到对话;
}
和这是会话类：
类对话
{
串发件人，于姓名，生物，图片;
整数ID，时间，未读;
公共会话（）{ }
公共会话（INT ID，字符串发件人，字符串，字符串名称，生物字符串，字符串的画面，诠释时间，INT读）{
this.sender =发送;
this.to =到;
this.id = ID;
this.name =名称;
this.bio =生物;
this.picture =图片;
this.time =时间;
this.unread =未读;
} 公共无效setSender（字符串发送）{
this.sender =发送;
}
公共无效setTo（字符串）{
this.to =到;
}
公共无效SETID（INT ID）{
this.id = ID;
}
公共无效的setTime（INT时间）{
this.time =时间;
}
公共无效setUnread（INT读）{
this.unread =未读;
}
公共无效increaseUnread（）{
this.unread ++;
}
公共无效setname可以（字符串名称）{
this.name =名称;
}
公共无效setBio（字符串生物）{
this.bio =生物;
}
公共无效setPicture（字符串图片）{
this.picture =图片;
} 公共字符串getSender（）{
返回this.sender;
}
公共字符串会过（）{
返回this.to;
}
公众诠释的getId（）{
返回this.id;
}
公众诠释的getTime（）{
返回this.time;
}
公众诠释getUnread（）{
返回this.unread;
}
公共字符串的getName（）{
返回this.name;
}
公共字符串getBio（）{
返回this.bio;
}
公共字符串Getpicture中（）{
返回this.picture;
}
}
你熟悉 notifyDataSetChanged（）和 notifyDataSetInvalidated（）在适配器的方法呢？数据集的每一个变化，这是用来在列表/方格被绘制后，你应该 updateConversations（conversationsList）之后调用这两个方法（可能是第一个）之一;
也：行新的ArrayList＆LT;会话＆GT;（conversationsMap.values（））; 应该做你的地图值的浅拷贝，检查的 //stackoverflow.com/questions/689370/java-collections-copy-list-i-dont-understand\">this堆栈线程获取更多信息。
I have a list and linkedhashmap.I am defining with following lines in top of main class:
List<Conversation> conversationsList=new ArrayList<Conversation>();
LinkedHashMap<String, Conversation> conversationsMap=new LinkedHashMap<String, Conversation>();
In onCreate() I am transferring data from db to hashmap then transferring map values to arraylist and I am using this arraylist in adapterview with following lines:
conversationsMap=_db.getAllConversations();
conversationsList=new ArrayList<Conversation>(conversationsMap.values());
conversationsAdapter=new ConversationsAdapter(this,conversationsList);
But there is something I don't understand.I can update the list with these lines:
conversationsMap.get(room_name).increaseUnread();
((ConversationsAdapter) conversationsAdapter).updateConversations(conversationsList);
It's working but I didn't update conversationsList why this is working I don't understand ? I just updated conversationsMap not the conversationsList. Can anyone explain to me why this is working ?
In db handler getAllConversations method:
public LinkedHashMap<String, Conversation> getAllConversations() {
List<Conversation> conversationsList=new ArrayList<Conversation>();
final LinkedHashMap<String, Conversation> conversations = new LinkedHashMap<String, Conversation>();
String selectQuery = "SELECT * FROM " + TABLE_CONVERSATIONS+" order by id asc";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
Conversation Conversation = new Conversation();
Conversation.setId(Integer.parseInt(cursor.getString(0)));
Conversation.setSender(cursor.getString(1));
Conversation.setTo(cursor.getString(2));
Conversation.setName(cursor.getString(3));
Conversation.setBio(cursor.getString(4));
Conversation.setPicture(cursor.getString(5));
Conversation.setTime(Integer.parseInt(cursor.getString(6)));
Conversation.setUnread(Integer.parseInt(cursor.getString(7)));
conversations.put(cursor.getString(2),Conversation);
} while (cursor.moveToNext());
}
cursor.close();
return conversations;
}
And this is the Conversation class:
class Conversation
{
String sender,to,name,bio,picture;
Integer id,time,unread;
public Conversation() {
}
public Conversation (int id,String sender,String to,String name,String bio,String picture,int time,int unread) {
this.sender=sender;
this.to=to;
this.id=id;
this.name=name;
this.bio=bio;
this.picture=picture;
this.time=time;
this.unread=unread;
}
public void setSender(String sender) {
this.sender=sender;
}
public void setTo(String to) {
this.to=to;
}
public void setId(int id) {
this.id=id;
}
public void setTime(int time) {
this.time=time;
}
public void setUnread(int unread) {
this.unread=unread;
}
public void increaseUnread() {
this.unread++;
}
public void setName(String name) {
this.name=name;
}
public void setBio(String bio) {
this.bio=bio;
}
public void setPicture(String picture) {
this.picture=picture;
}
public String getSender() {
return this.sender;
}
public String getTo() {
return this.to;
}
public int getId() {
return this.id;
}
public int getTime() {
return this.time;
}
public int getUnread() {
return this.unread;
}
public String getName() {
return this.name;
}
public String getBio() {
return this.bio;
}
public String getPicture() {
return this.picture;
}
}
are you familiar with notifyDataSetChanged() and notifyDataSetInvalidated() methods in your adapter? after every change of data set which is used to be drawn in List/Grid you should call one of these two methods (probably first one) after updateConversations(conversationsList);
also: line new ArrayList<Conversation>(conversationsMap.values()); should do a shallow copy of your map values, check this stack thread about set copying for more info
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