我正在尝试在用户滚动列表时更新listView的列表,并为用户提供继续和滚动新条目的选项,但是没有成功,我需要帮助。
在我的应用程序中,我正在聊天,并且正在SQLite中保存聊天的历史记录。当用户进入聊天时,应用程序仅读取最后25条消息,并在列表底部显示最新消息。 为了做到这一点,我在XML上使用了以下选项:
android:transcriptMode="alwaysScroll"
android:stackFromBottom="true"
,它工作正常。 现在,当用户开始向上滚动并查看聊天记录时,当他到达列表顶部时,我正在访问数据库并检索另外25条消息,并将它们添加到列表顶部,并且打电话给: chatAdaptor.notifyDataSetChanged();
但是当用户试图向上滚动时,什么也没有呈现,只有在向下和向上滚动之后,才会显示新条目。
我已经尝试使用setSelection和smoothScrollToPosition设置列表视图的位置,但这确实不起作用。
如何使用新条目更新列表,并为用户提供继续滚动和向上滚动的选项?
这是相关代码:
<ListView
android:id="@+id/chatList"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="bottom"
android:layout_margin="2dp"
android:layout_weight="1"
android:transcriptMode="alwaysScroll"
android:stackFromBottom="true"
android:background="@drawable/frame_tab"></ListView>
public void showChatLines() {
chatLinesView = chatTextDialog.findViewById(R.id.chatList);
chatAdaptor = new GenericAdapter<ChatLine>(activity, chatLines) {
@Override
public View getMyView(int position, View convertView, ViewGroup parent, ChatLine chatLine) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(R.layout.chat_line, null);
TextView chatLineText = view.findViewById(R.id.chatLine);
chatLineText.setText(chatLine.messageText);
TextView chatLineTime = view.findViewById(R.id.chatLineTime);
chatLineTime.setText(chatLine.displayDateTime);
TextView chatLineUserName = view.findViewById(R.id.userName);
chatLineUserName.setText(chatLine.userDisplayName);
chatLineUserName.setTextColor(activity.getColor(Constants.colors[getColorBy(chatLine.userName)]));
LinearLayout chatLineLayout = view.findViewById(R.id.chatLineLayout);
LinearLayout.LayoutParams chatLineLayoutParams = (LinearLayout.LayoutParams) chatLineLayout.getLayoutParams();
CardView chatLineBackground = view.findViewById(R.id.chatLineBackground);
LinearLayout.LayoutParams chatLineBackgroundParams = (LinearLayout.LayoutParams) chatLineBackground.getLayoutParams();
LinearLayout chatLineSubLayout = view.findViewById(R.id.chatLineSubLayout);
FrameLayout.LayoutParams chatLineSubLayoutParams = (FrameLayout.LayoutParams) chatLineSubLayout.getLayoutParams();
if (chatLine.userName.equals(logonUserName)) {
CardView charLineCard = view.findViewById(R.id.chatLineBackground);
charLineCard.setCardBackgroundColor(activity.getColor(R.color.focusedColor));
((ViewGroup) chatLineUserName.getParent()).removeView(chatLineUserName);
} else {
chatLineLayoutParams.gravity = Gravity.RIGHT;
chatLineLayout.setLayoutParams(chatLineLayoutParams);
chatLineSubLayoutParams.gravity = Gravity.RIGHT;
chatLineSubLayout.setLayoutParams(chatLineSubLayoutParams);
chatLineBackgroundParams.gravity = Gravity.RIGHT;
chatLineBackground.setLayoutParams(chatLineBackgroundParams);
}
if (position==0 & fromLine!=0) {
getNextChatLinesFromDb(position);
}
return view;
}
};
chatLinesView.setAdapter(chatAdaptor);
}
private void getNextChatLinesFromDb(int position) {
toLine = fromLine - 1;
fromLine -= pageSize;
if (fromLine < 0) {
fromLine = 0;
}
ArrayList<ChatLine> newChatLines = db.getChatLines(chatRoomId, fromLine, toLine);
chatLines.addAll(0, newChatLines);
chatAdaptor.notifyDataSetChanged();
}
答案 0 :(得分:0)
我认为这段代码将为您提供帮助:
// get position of listview
int index = chatLinesView.getFirstVisiblePosition();
View v = chatLinesView.getChildAt(0);
int top = (v == null) ? 0 : v.getTop();
// notify dataset changed or re-assign adapter here
//re-assign the position of listview after setting the adapter again
chatLinesView.setSelectionFromTop(index, top);
修改
int h1 = chatLinesView.getHeight();
int h2 = chatLinesViewRow.getHeight();
chatLinesView.smoothScrollToPositionFromTop(position, h1/2 - h2/2, duration);
参数 位置->滚动到的位置
offset ---->距像素顶部所需位置的距离(以像素为单位) 滚动完成后查看
duration->用于滚动的毫秒数
答案 1 :(得分:0)
请尝试以下示例代码:
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<ListView
android:id="@+id/listView"
android:transcriptMode="alwaysScroll"
android:stackFromBottom="true"
android:layout_width="match_parent"
android:layout_height="match_parent"></ListView>
</LinearLayout>
MainActivity.java
public class MainActivity extends AppCompatActivity implements AbsListView.OnScrollListener{
final static private int ADD_DATA_SIZE = 10;
ArrayList<String> dataList;
ListView listView;
ArrayAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dataList = new ArrayList<>();
for(int i=0; i<30; i++){
dataList.add("Item " + i);
}
listView = findViewById(R.id.listView);
adapter = new ArrayAdapter<>(getApplicationContext(), android.R.layout.simple_list_item_1, dataList);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Toast.makeText(getApplicationContext(), adapterView.getItemAtPosition(i) + " Clicked!", Toast.LENGTH_SHORT).show();
}
});
listView.setOnScrollListener(this);
}
private void addNewData() {
ArrayList<String> tmpList = new ArrayList<>();
for(int i=0; i<ADD_DATA_SIZE; i++){
tmpList.add("Add " + (dataList.size() - 20)/10 + ": Item " + i);
}
dataList.addAll(0, tmpList);
listView.setSelection(ADD_DATA_SIZE);
adapter.notifyDataSetInvalidated();
}
@Override
public void onScrollStateChanged(AbsListView absListView, int i) {}
@Override
public void onScroll(AbsListView absListView, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if(firstVisibleItem == 0){
View view = absListView.getChildAt(0);
if(view != null){
if (view.getTop() == absListView.getTop()) {
absListView.setTranscriptMode(AbsListView.TRANSCRIPT_MODE_DISABLED);
Toast.makeText(getApplicationContext(), "TRANSCRIPT MODE CHANGED TO: "
+ absListView.getTranscriptMode(), Toast.LENGTH_SHORT).show();
addNewData();
}
}
} else if (totalItemCount == (firstVisibleItem + visibleItemCount)){
View view = absListView.getChildAt(visibleItemCount - 1);
if (view.getBottom() == absListView.getBottom()) {
absListView.setTranscriptMode(AbsListView.TRANSCRIPT_MODE_ALWAYS_SCROLL);
Toast.makeText(getApplicationContext(), "TRANSCRIPT MODE CHANGED TO: "
+ absListView.getTranscriptMode(), Toast.LENGTH_SHORT).show();
}
}
}
}
希望有帮助!