I'm new to Android and I know this is very common question. I tried to look for answers but it didn't satisfy my curiosity. Supposed that I have code below to define a listener for a button in Android. I'm still confusing about the this . I know "this" refers to the current instance but in this case, what does "this" refer to ? Does it point to the instance btnSave or which else objects ? Why can it replace the argument (new OnClickListener())
Supposed that I have two identical button. How does the method Onclick know which one is clicked ??? Can someone clarify the purpose of "this" in an broader situation ?
Button btnSave = (Button) findViewById(R.id.btnSave);
btnSave.setOnClickListener(this);
public void onClick(View v) {
//Do something in here
}
Here, this refers to reference to the current object, the container that had the btnSave in this case. The intention is the the container will listen to Click events taking place on the button to take further action through the listener method i.e. onClick.
Related
<mat-checkbox (change)="handleProductClick(children, $event)" [(ngModel)] = "children.selected"
[name]="children.grpId" [id]="children.id"></mat-checkbox>
handleProductClick(selectedProd : Product, event: any)
{
event.stopPropagation();
}
If I use click function instead of change it works fine. Although I can't use click. I have to stick with change. Is there a way to call stopPropagation from change function? If not what else can I do to stop the event propagation?
I got it working. Had to use both click and change on the checkbox. I had tried that earlier. The only difference was I was calling a function in the click method and it never got called. If you call $event.stopPropagation on click method in the template, it works well. strange. The below answer solved my problem. Angular 2 prevent click on parent when clicked on child
<mat-checkbox (change)="handleProductClick(children, $event)"[checked]="children.selected" (click)="$event.stopPropagation()"
[name]="children.grpId" [id]="children.id"></mat-checkbox>
I found two ways to allegedly make the help work for an Eclipse wizard.
The first is to set setHelpAvailable(true) on my instance of Wizard and let the WizardPage override the method:
public void performHelp() {
PlatformUI.getWorkbench().getHelpSystem().displayHelp(CONTEXT_ID);
}
It displays a help button without an icon next to the "Back" button, but the method performHelp is never called.
The second way is to set it on the TrayDialog directly like this:
WizardDialog dialog = new WizardDialog(myShell, myWizard);
dialog.create();
WorkbenchHelp.setHelp(dialog.getShell(), CONTEXT_ID);
dialog.setHelpAvailable(true);
dialog.open();
This displays a button with an icon on the bottom left, but nothing happens when I click it.
The help system is set up (quiet a feat with the documentation, if I say so myself), but I can't figure out how to get either of these solutions to work. And I wonder if one of them should preferred over the other?
With the WizardDialog just call
dialog.setHelpAvailable(true);
In the createControl method of each WizardPage call the help system setHelp:
public void createControl(Composite parent)
{
Composite composite = new Composite(parent, SWT.NONE);
PlatformUI.getWorkbench().getHelpSystem().setHelp(composite, "help id");
... other code
Just for completeness sake: In my case the problem had nothing to do with the sparsely documented help feature, but with the fact that Eclipse Mars can't Hot Code Replace anymore.
I have an object I want to drag around the screen with the mouse in Processing. I set acquired to true on mouse down over the object, and to false on mouse up, thus:
void mousePressed() {
if (overThing()) {
acquired = true;
}
}
void mouseReleased() {
acquired = false;
}
I then query acquired in my update(), and drag the object if it is true.
void update() {
\\ other stuff...
if (acquired) {
\\ drag thing code ...
}
}
This all works fine in Processing. mouseReleased() gets called whether I release the mouse inside or outside the active window.
However, when I move the code to Chrome, using processing.js (v1.4.8), mouseReleased() is not called if I release the mouse outside the canvas (whether the mouse is still over the web page, or outside the browser window). So when I return the (now unclicked) mouse to the canvas, the object is still getting dragged around.
I tried including a test of mousePressed in update(), but that also returns true in these circumstances.
Any help on what I need to do to make mouse state changes outside the canvas visible with processing.js?
I don't know about Processing specifically, but releasing mouse buttons outside a widget is a common issue in GUI development.
I suspect that you have no way of knowing the precise time when the mouse is released outside the widget, but you do have two options:
Set acquired = false in mouseOut(), as #Kevin suggests.
I assume there is some type of mouseEntered() method in Processing, and also some way of knowing if the mouse button is currently pressed (either a global variable, or an event object passed to mouseEntered()). You can catch the mouse entered event, check if the mouse has been released, and set acquired = false then.
Like so:
void mouseEntered() {
if (mouse button is pressed) {
acquired = false;
}
}
Edit: From your comments, #Susan, it seems like there is a bug in processing.js, where mousePressed is not set to false if the mouse button is released outside the canvas. One thing pointing to this being a bug is that the mouse movement example on the processing website also shows this behaviour.
Depending upon how much control you have over the website this is going on, and how much effort you want to go to, you could fix the bug yourself by writing some javascript (separate from your processing code):
Define a mouseUp() event on the page <body>, to catch all mouse release events on the page.
In the mouseUp() event, check if the event comes from your Processing control. (There is probably an event object passed to the mouseUp() function, and you might have to give your Processing control an ID to identify it)
If the event doesn't come from your Processing control, then fire a mouseUp event yourself, on the Processing control. This should (hopefully!) trigger a mouse event inside your Processing code.
I'm not sure what Processing will make of the mouse (x,y) position being outside its control when it handles the event you send it. You might want to set a flag on the event object (assuming you can add extra data to the event object) to say "don't use the (x,y) position of this event - it's outside the control".
Edit2: It was easier than I thought! Here is the JavaScript code to detect the mouse being released outside of the Processing canvas and send the mouseReleased event to the canvas. I've tested it on the mouse movement example from the Processing website, and it fixes the bug.
It uses jQuery (although it could be re-written to not use jQuery), and it assumes your Processing canvas has the ID "processingCanvas":
$(':not(processingCanvas)').mouseup(function(){
Processing.getInstanceById('processingCanvas').mouseReleased();
});
To use this code, include it anywhere in your page (in a JavaScript file or in <script> tags) and make sure you have the jQuery library included before this code.
The Processing object allows JavaScript to call any functions defined in your Processing code. Here I've used it to call Processing's built in mouseReleased() function, but if you wanted to call a custom function to handle the mouse-released-outside state differently, then you could.
You should use the mouseOut() function to detect when the mouse leaves the sketch:
void mouseOut() {
acquired = false;
}
More info in the reference here.
There are a lot of samples showing how to pass a parameter on navigating to a page in Window 8 (WinRT). But I could not find any hint for passing parameters going back.
Situation: The user navigates to a details page of same data. The data is passed to the page by
Frame.Navigate(typeof(DedtailsPage), data);
How can I pass back the changed data on GoBack()?
Store the reference to data somewhere and retrieve it when you navigate back?
Also note that it's best not to pass objects other than simple strings or values between pages, since only simple types are supported for storing frame navigation state in case your app gets suspended.
I know, that this is a very bad idea, but usualy I use this:
To write:
Frame rootFrame = Window.Current.Content as Frame;
rootFrame.Tag = myObject1;
To read:
Frame rootFrame = Window.Current.Content as Frame;
var myObject2 = rootFrame.Tag;
I've made another choice to handle this.
Keep in mind that I'm a Xamarin developer (not Forms!) so i was looking for a solution which was similar for all platforms: iOS, Android and Windows.
I am a great fun of events, rather than passing objects or storing globals.
So the best choice to pass data from PageB (the child) to PageA (the parent) is to communicate via events.
Some notes: In iOS and Android, when you navigate from a "page" to "page" you can do this by passing an instance of the target object you want to navigate to. In iOS you create an instance of a custom UIViewController. In Android you create an instance of a custom Fragment. Doing this allow you to attach events handler to your instances.
An example:
var controller = new ExtrasViewController();
controller.ExtraSelected += ExtrasFragment_ExtraSelected;
controller.ExtrasCleared += ExtrasFragment_ExtrasCleared;
this.NavigationController.PushViewController(controller, false);
In WinRT Apps you are only allowed to pass "types" of target page to navigate to. So the only way to attach event handlers to your page instance is to use the OnNavigatedFrom method from the calling page. So suppose you are in PageA and want to attach some event handlers to your PageB, before it become active, simply write in your PageA "code behind":
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
base.OnNavigatedFrom(e);
var page = e.Content as ExtraBody;
if(page != null)
{
page.ExtraSelected += ExtrasFragment_ExtraSelected;
page.ExtrasCleared += ExtrasFragment_ExtrasCleared;
}
}
I have to port some legacy code, that uses modal dialog boxes all over the place to Metro/WinRT (using C++/CX). Because these dialog boxes provide their own message loop (using DialogBoxParam()), the calling code will wait until the user has clicked a button on the message box.
I'm currently trying to write a replacement for the old message box class, that uses XAML and the popup control. To reproduce the same behavior, I have to wait in the calling thread, but also have to keep the UI responsive. I've found out, that CoreDispatcher::ProcessEvents() can be used in a loop, to keep processing events (yeah I realize that this isn't very beautiful, but I don't want to change all of our legacy code to a new threading model). However I'm running into an issue that keeps crashing my app.
Here is a minimal example that reproduces the issue (just create a XAML app and wire this to a button):
void CPPXamlTest::MainPage::Button_Click_1(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
bool cancel = false;
auto popup = ref new Popup();
auto button = ref new Button();
button->Content = "Boom";
auto token = (button->Click += ref new RoutedEventHandler([&cancel] (Object ^, RoutedEventArgs ^) { cancel = true; }));
popup->Child = button;
popup->IsOpen = true;
while (!cancel)
{
Window::Current->Dispatcher->ProcessEvents(CoreProcessEventsOption::ProcessOneAndAllPending);
}
popup->IsOpen = false;
button->Click -= token;
}
This seems to work well for the first one or two tries of opening and closing the popup, using the two buttons. After a few tries however, the application will instantly crash deep in Windows.UI.Xaml.dll, while trying to dereference a null pointer. I can also reproduce this in C# (with practically the same code).
Does anyone have an idea, what is going on in here? Or a suggestion for an alternative approach?
If anyone is interested: I asked the same question a few days later on the MSDN forums and got a response there from a Microsoft employee:
http://social.msdn.microsoft.com/Forums/en-US/winappswithnativecode/thread/11fa65e7-90b7-41f5-9884-80064ec6e2d8/
Apparently the problem here is the nested message loop that is caused by calling ProcessEvents inside an event handler. It seems that this is not supported by WinRT, but instead of failing in a well-defined manner, this will or may cause a crash.
Alas this was the best and only answer I could find, so I ended up working around the problem, by dispatching the event handler (and a lot of other code) into another thread. I could then emulate the waiting behavior of DialogBox()/DialogBoxParam() (outside the main thread), by waiting on an event that was signaled when the user clicked/tapped a button on my XAML "dialog" popup.
A workaround that works fine for me is to replace the line:
Window::Current->Dispatcher->ProcessEvents(CoreProcessEventsOption::ProcessOneAndAllPending);
with:
auto myDispatchedHandler = ref new DispatchedHandler([&](){
Window::Current->Dispatcher->ProcessEvents(CoreProcessEventsOption::ProcessOneAndAllPending);
});
dispatcher->RunAsync(CoreDispatcherPriority::Normal,myDispatchedHandler);
For more info see this post at MSDN.