Attention! This question is not about dynamic loading of items into a very long ListView.
This is about adding PageUP and PageDown buttons to a ListView so that user can touch the button and scroll ListView page by page. Page means all fully and partially visible items on the screen.
I have partially implemented this in the following code, but my problem is that when I have lets say 10 items of approximately same height in the listview and 7 of them fit into the first page, then when I press PgDown button, user expects that item 8 to be on top of the screen (next page), but because there are only 10 items, ListView scrolls to the bottom of the list and because there is no extra scroll space I have item number 4 on top. What is the best solution in this situation? Should I add one item to the end of the list which will make the last page the height of the screen or there are any better options?
Here is my code:
public class cPaginatedListViewHelper {
Activity m_parentActivity;
private ListView mList;
//controls
private LinearLayout m_PagingLL;
//buttons
private ImageButton m_btnPrevPage;
private ImageButton m_btnNextPage;
private ImageButton m_btnExitPaginatedMode;
public cPaginatedListViewHelper(ListActivity mParent) {
this.m_parentActivity = mParent;
m_btnPrevPage=(ImageButton) mParent.findViewById(R.id.btnPrevPage);
m_btnNextPage=(ImageButton) mParent.findViewById(R.id.btnNextPage);
m_btnExitPaginatedMode =(ImageButton) mParent.findViewById(R.id.btnClosePage);
if(m_btnPrevPage!=null) {
m_btnPrevPage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showSiblingPage(-1);
}
});
m_btnPrevPage.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
mList.smoothScrollToPosition(0);
return true;
}
}
);
}
if(m_btnNextPage!=null) {
m_btnNextPage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showSiblingPage(1);
}
});
m_btnNextPage.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
mList.smoothScrollToPosition(mList.getCount());
return true;
}
}
);
}
m_btnExitPaginatedMode.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
setEnabled(false);
m_PagingLL.setVisibility(View.GONE);
}
});
mList=mParent.getListView();
m_PagingLL = (LinearLayout) mParent.findViewById(R.id.pageControls);
}
public void updateControlsVisibility()
{
ViewTreeObserver observer = mList.getViewTreeObserver();
observer.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
if (willMyListScroll()) {
boolean psm = isEnabled();
//enable or disable
m_PagingLL.setVisibility( psm ? View.VISIBLE : View.GONE);
((View)mList).setVerticalScrollbarPosition(psm ? View.SCROLLBAR_POSITION_LEFT: View.SCROLLBAR_POSITION_RIGHT);
}
else
{
m_PagingLL.setVisibility(View.GONE);
((View)mList).setVerticalScrollbarPosition(View.SCROLLBAR_POSITION_RIGHT);
}
}
});
}
private boolean willMyListScroll() {
try {
int pos = mList.getLastVisiblePosition();
if (mList.getChildAt(pos).getBottom() > mList.getHeight()) {
return true;
} else {
return false;
}
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
private void showSiblingPage(int shift)
{
if(mList!=null) {
int iScrollPageHeight = mList.getHeight();
mList.scrollListBy(iScrollPageHeight * shift);
}
}
public void setEnabled(boolean psm) {
MyApp.Pref.edit().putBoolean("PSModeEnabled", psm).commit();
}
public boolean isEnabled(){
return MyApp.Pref.getBoolean("PSModeEnabled", false);
}
public void pagedScrollEnableDisable() {
boolean pagingEnabled = isEnabled();
pagingEnabled=!pagingEnabled;
setEnabled(pagingEnabled);
m_PagingLL.setVisibility( pagingEnabled ? View.VISIBLE : View.GONE);
updateControlsVisibility();
}
}
I finished up with using ListView's footer with variable height as shown in the following code:
LayoutInflater inflater = m_parentActivity.getLayoutInflater();
m_footerView = inflater.inflate(R.layout.listview_paged_overscroll, mList, false );
ViewGroup.LayoutParams lp =m_footerView.getLayoutParams();
if(m_tvPageNum!=null) recalcPagination();
if(lp!=null) lp.height = m_extraScrollFooterHeight;
int iFooters = mList.getFooterViewsCount();
if(iFooters==0) mList.addFooterView(m_footerView);