I am using TabbedPage for navigation with tabs. All my Page classes have just an empty default constructor and I load my data in the OnAppearing method. I have 5 tabs. As soon as I click on the second tab, the OnAppearing methods of the 3rd, 4th and 5th pages are also called.
How do I ensure that the data is only loaded when I click on the tab?
Solution:
You can get the index of currentPage in method OnCurrentPageChanged And if the index equals 1(second page) , use the messagecenter to send message to the page.Refer the following code .
in Tabbed Page
protected override void OnCurrentPageChanged()
{
base.OnCurrentPageChanged();
int index = Children.IndexOf(CurrentPage);
if (index == 1)
{
MessagingCenter.Send<Object>(this, "click_second_tab");
}
else if (index == 2)
{
MessagingCenter.Send<Object>(this, "click_third_tab");
}
}
in the second page .Move the code that load data from onAppearing to the constructor
public MyPage1()
{
//...
MessagingCenter.Subscribe<Object>(this, "click_second_tab", (obj) =>
{
//load your data here
Console.WriteLine("11111");
});
}
Related
So, I have a listview and I want it whenever an item is created to scroll to that item (bottom). Because I am using MVVM I found really nice explanation on how to make a new control that inherits from listview that scrolls down. The problem is that this answer (the third) is referring to WPF 6 years ago.
I am making a UWP app, so I copied the code and tried to format it to my needs. The following code doesn't give any error or exception but instead it loads the "ChatListView" as I call it perfectly and then does nothing. The comments are only a bit edited compared to the original code.
What can I do ? Thank you in advance!
public class ChatListView : ListView
{
//Define the AutoScroll property. If enabled, causes the ListBox to scroll to
//the last item whenever a new item is added.
public static readonly DependencyProperty AutoScrollProperty =
DependencyProperty.Register(
"AutoScroll",
typeof(Boolean),
typeof(ChatListView),
new PropertyMetadata(
true, //Default value.
new PropertyChangedCallback(AutoScroll_PropertyChanged)));
//Gets or sets whether or not the list should scroll to the last item
//when a new item is added.
public bool AutoScroll
{
get { return (bool)GetValue(AutoScrollProperty); }
set { SetValue(AutoScrollProperty, value); }
}
//Event handler for when the AutoScroll property is changed.
//This delegates the call to SubscribeToAutoScroll_ItemsCollectionChanged().
//d = The DependencyObject whose property was changed.</param>
//e = Change event args.</param>
private static void AutoScroll_PropertyChanged(
DependencyObject d, DependencyPropertyChangedEventArgs e)
{
SubscribeToAutoScroll_ItemsCollectionChanged(
(ChatListView)d,
(bool)e.NewValue);
}
//Subscribes to the list items' collection changed event if AutoScroll is enabled.
//Otherwise, it unsubscribes from that event.
//For this to work, the underlying list must implement INotifyCollectionChanged.
//
//(This function was only creative for brevity)
//listBox = The list box containing the items collection.
//subscribe = Subscribe to the collection changed event?
private static void SubscribeToAutoScroll_ItemsCollectionChanged(
ChatListView listView, bool subscribe)
{
INotifyCollectionChanged notifyCollection =
listView as INotifyCollectionChanged;
if (notifyCollection != null)
{
if (subscribe)
{
//AutoScroll is turned on, subscribe to collection changed events.
notifyCollection.CollectionChanged +=
listView.AutoScroll_ItemsCollectionChanged;
}
else
{
//AutoScroll is turned off, unsubscribe from collection changed events.
notifyCollection.CollectionChanged -=
listView.AutoScroll_ItemsCollectionChanged;
}
}
}
//Event handler called only when the ItemCollection changes
//and if AutoScroll is enabled.
//sender = The ItemCollection.
//e = Change event args.
private void AutoScroll_ItemsCollectionChanged(
object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
int count = Items.Count;
ScrollIntoView(Items[count - 1]);
}
}
//Constructor a new ChatListView.
public ChatListView()
{
//Subscribe to the AutoScroll property's items collection
//changed handler by default if AutoScroll is enabled by default.
SubscribeToAutoScroll_ItemsCollectionChanged(
this, (bool)AutoScrollProperty.GetMetadata(typeof(ChatListView)).DefaultValue);
}
}
If you want to create a chat application you can use the ItemsStackPanel's ItemsUpdatingScrollMode particular property to KeepLastItemInView value to scroll to the latest item.
Usage:
<ListView>
<ListView.ItemsPanel>
<ItemsPanelTemplate>
<ItemsStackPanel ItemsUpdatingScrollMode="KeepLastItemInView" />
</ItemsPanelTemplate>
</ListView.ItemsPanel>
</ListView>
Note: KeepLastItemInView enum member was introduced in the 14393 SDK.
Related link:
https://learn.microsoft.com/en-us/uwp/api/Windows.UI.Xaml.Controls.ItemsStackPanel#properties_
The accepted answer is pretty nice. However I there is one thing it won't do (at least if I simply copy and paste the above XAML): it won't do its intended scrolling if, say, the user was away from that page while new items were added, and then they navigated to the page.
For that I had to hook into
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
if (MyListView.Items.Count == 0)
return;
object lastItem = MyListView.Items[MyListView.Items.Count - 1];
MyListView.ScrollIntoView(lastItem);
}
In my firefox sdk addon, I want to use a custom webpage from my data directory as my settings/about page.
But I am having trouble keeping tabs on the tab!
So I have a button that calls the OptionsPanel() function to open my webpage in a new tab. Now, I want to make it so if the user forgets that tab is open and pushes the button again, that it activates the already-open settings tab. That means I need to know that the tab is open and I need to be able to switch to it if it is OR open it if it is not already open.
Here is what I've come up with so far, but it doesn't work; it just always opens a new tab. I don't even know if I'm barking up the right tree.
const tabs = require("sdk/tabs");
var optionsTab;
function OptionsPanel(){
var opsTab = GetTabByID(optionsTab.id);
if(opsTab == null){
tabs.open( data.url("OptionsPanel.html") );
optionsTab.id = tabs.tab.id; <======errors out as undefined
}else{
opsTab.activate();
}
}
//return a handle to the tab that matches specified tab id
function GetTabByID(whatid){
for(let thistab of tabs){
if(thistab.id = whatid){
return thistab;
}
}
return null;
}
So, here are my goals:
Open my page in a new tab if it isn't already open.
If the tab is already open, then switch to that tab.
If the page is open when the browser loads, then be ready to switch to that tab if the user pushes the options button.
Why would you think tabs module has a tab property?
Normally you would use the activeTab property instead. However it does not get updated immediately after tabs.open is called. One has to use tabs[tabs.length - 1] instead.
const tabs = require("sdk/tabs");
var optionsTabId;
function OptionsPanel(){
var opsTab = GetTabByID(optionsTabId);
if (opsTab == null) {
tabs.open( data.url("OptionsPanel.html") );
optionsTabId = tabs[tabs.length - 1].id;
} else {
opsTab.activate();
}
}
Additionally, you made a mistake in GetTabByID.
//return a handle to the tab that matches specified tab id
function GetTabByID(whatid){
for(let thistab of tabs){
if(thistab.id == whatid){ // use == to compare
return thistab;
}
}
return null;
}
Keep in mind this assumes that it is not possible to navigate away from your options tab. I would check optsTab.url just in case.
Alternatively you could make use of the tab event interface
const tabs = require("sdk/tabs");
const OPTIONS_URL = data.url("OptionsPanel.html");
var optionsTab = null;
function OptionsPanel(){
if (optionsTab == null) {
tabs.open(OPTIONS_URL);
tabs.once('ready', function(tab) {
optionsTab = tab;
optionsTab.on('ready', function readyListener(tab) {
if (tab.url !== OPTIONS_URL) {
optionsTab.off('ready', readyListener);
optionsTab = null;
}
})
optionsTab.once('close', function(tab) {
optionsTab = null;
})
});
} else {
optionsTab.activate();
}
}
I want to implement menu in GWT as shown on this website:
http://www.openkm.com/en/
I have created the menu system and I am able to display alerts from menu using following code:
Command cmd = new Command() {
public void execute() {
Window.alert("Menu item have been selected");
}
}
I want to get rid of window.alert() and display my application pages from menu.
Create and load the appropriate page. For example if you use UiBinder then:
MyPage selectedPage = new MyPage(); // creating of your panel
RootPanel.get().clear(); // cleaning of rhe RootPanel
RootPanel.get().add(selectedPage); // adding the panel to the RootPanel
First create an array list of views
public List<UIObject> viewsList = new ArrayList<UIObject>();
Add a view to that list
viewsList.add(addMovieView);
Send the view you want to select to the helper method
public void changeView(UIObject selectedView) {
for(UIObject view : viewsList) {
if(selectedView.equals(view)) {
view.setVisible(true);
} else {
view.setVisible(false);
}
}
}
Are you trying to make the entire page GWT, or just the menu? If it's just the menu, you will need to embed a GWT element into your overall HTML, then call something like
Window.open(linkURL, "_self", "");
from the appropriate menu items, which will navigate to another page.
I have a tabpanel with 3 tabs. One of the tabs has a table which draws a table with data from the database. But if new data is entered, after I select the tab I have to refresh the browser page to see the update.
I've added the following selection handler to the tabpanel:
tabpanel.addSelectionHandler(new SelectionHandler<Integer>()
{
public void onSelection(SelectionEvent<Integer> event)
{
int tabId = event.getSelectedItem();
Widget tabWidget = tabpanel.getWidget(tabId);
if (tabWidget != null)
{
//assumming that code to refresh will go here...
}
}
});
What can I do so that when a certain tab is selected then that tab will refresh?
Thanks so much in advance.
What you have done is correct. Just put your data access code in the commented area. So for example
int tabId = event.getSelectedItem();
// PSEUDO CODE
data = AsyncCallback.getData()
tabPanel.setWidget(tabId, new Widget(data)); // PSEUDO CODE
GWT's CellBrowser is a great way of presenting dynamic data.
However when the browser contains more rows than some (seemingly) arbitrary maximum, it offers a "Show More" label that the user can click to fetch the unseen rows.
How can I disable this behavior, and force it to always show every row?
There are several ways of getting rid of the "Show More" (which you can combine):
In your TreeViewModel, in your NodeInfo's setDisplay or in the DataProvider your give to the DefaultNodeInfo, in onRangeChange: overwrite the display's visible range to the size of your data.
Extend CellBrowser and override its createPager method to return null. It won't change the list's page size though, but you can set it to some very high value there too.
The below CellBrowser removes the "Show More" text plus loads all available elements without paging.
public class ShowAllElementsCellBrowser extends CellBrowser {
public ShowAllElementsCellBrowser(TreeViewModel viewModel, CellBrowser.Resources resources) {
super(viewModel, null, resources);
}
#Override
protected <C> Widget createPager(HasData<C> display) {
PageSizePager pager = new PageSizePager(Integer.MAX_VALUE);
// removes the text "Show More" during loading
display.setRowCount(0);
// increase the visible range so that no one ever needs to page
display.setVisibleRange(0, Integer.MAX_VALUE);
pager.setDisplay(display);
return pager;
}
}
I found a valid and simple solution in setting page size to the CellBrowser's builder.
Hope this will help.
CellBrowser.Builder<AClass> cellBuilder = new CellBrowser.Builder<AClass>(myModel, null);
cellBuilder.pageSize(Integer.MAX_VALUE);
cellBrowser = cellBuilder.build();
The easiest way to do this is by using the:
cellTree.setDefaultNodeSize(Integer.MAX_VALUE);
method on your Cell Tree. You must do this before you begin expanding the tree.
My workaround is to navigate through elements of treeview dom to get "show more" element with
public static List<Element> findElements(Element element) {
ArrayList<Element> result = new ArrayList<Element>();
findShowMore(result, element); return result; }
private static void findShowMore(ArrayList res, Element element) {
String c;
if (element == null) { return; }
if (element.getInnerText().equals("Show more")) { res.add(element);
}
for (int i = 0; i < DOM.getChildCount(element); i++) { Element
child = DOM.getChild(element, i); findShowMore(res, child); } }
and than use:
if (show) { element.getStyle().clearDisplay(); } else {
element.getStyle().setDisplay(Display.NONE); }