How do I continue from the last screen I open in my app after I exited.
Say for example I have screen A, B and C and I was on screen B before I close the application. My question is how do I get to screen B when I reopen the app again.
Use SharedPreferences to save the value in int for screen A, B and C as 1, 2 and 3 respectively when their initState() method fires (to get an idea respective screen is open)
When you open the app next time, you can get the int value and use a switch to decide what to load.
void main() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
Widget rootWidget;
switch (prefs.getInt("key")) {
case 1:
rootWidget = Page1();
break;
case 2:
rootWidget = Page2();
break;
case 3:
rootWidget = Page3();
break;
}
runApp(MaterialApp(home: rootWidget));
}
Related
I have a CameraPreview that fills the whole screen, with a FloatingActionButton at the bottom to take a picture.
On the onPress method of the button, I'm making a network call for which I do not care (yet) about the result. So I would like everything made inside that method to be done asynchronously, so it does not block my main thread.
That means (if I get it right) that I sould not use the await keyword.
This is the code in my onPressed
// Attempt to take a picture and log where it's been saved
await controller.takePicture(path);
print("Done taking picture");
sendBase64ToAPI(path);
This is my sendBase64ToApi method
Future<String> sendBase64ToAPI(String path) async {
File(path).readAsBytes().then(thenMethod);
return null;
}
void thenMethod(List bytes){
print("Start reading file");
Image image = decodeImage(bytes);
int x = ((screenWidth/2) + (overlayWidth/2)).toInt();
int y = ((screenHeight/2) + (overlayHeight/2)).toInt();
print("Start cropping image");
image = copyCrop(image, x, y, overlayWidth, overlayHeight);
var base64Str = base64.encode(image.getBytes());
print("Done");
print(base64Str.substring(0,30));
print(base64Str.substring(base64Str.length-30,base64Str.length-1));
}
My UI is completely frozen between 'Start reading file' and 'Start cropping image' although, those are async methods, called without await so that shouldn't happen.
Why are those methods not executing asynchronously ?
Okay, this seems to be a known issue from the library I'm using.
The documentation recommends to use the decodeImage function in an Isolate.
Will keep the question open for a few days, if someone spots what is synchronous in my code.
I'm developing a BlackJack game for iOS. Keeping track of the current state and what needs to be done is becoming difficult. For example, I have a C++ class which keeps track of the current Game:
class Game {
queue<Player> playerQueue;
void hit();
void stand();
}
Currently I'm implementing it using events (Method A):
- (void)hitButtonPress:(id)sender {
game->hit();
}
void Game::hit() {
dealCard(playerQueue.top());
}
void Game::stand() {
playerQueue.pop();
goToNextPlayersTurn();
}
as more and more options are added to the game, creating events for each one is becoming tedious and hard to keep track of.
Another way I thought of implementing it is like so (Method B):
void Game::playersTurn(Player *player) {
dealCards(player);
while (true) {
string choice = waitForUserChoice();
if (choice == "stand") break;
if (choice == "hit")
dealCard(player);
// etc.
}
playerQueue.pop();
goToNextPlayersTurn();
}
Where waitForUserChoice is a special function that lets the user interact with the UIViewController and once the user presses a button, only then returns control back to the playersTurn function. In other words, it pauses the program until the user clicks on a button.
With method A, I need to split my functions up every time I need user interaction. Method B lets everything stay a bit more in control.
Essentially the difference between method A and B is the following:
A:
function A() {
initialize();
// now wait for user interaction by waiting for a call to CompleteA
}
function CompleteA() {
finalize();
}
B:
function B() {
initialize();
waitForUserInteraction();
finalize();
}
Notice how B keeps the code more organized. Is there even a way to do this with Objective-C? Or is there a different method which I haven't mentioned recommended instead?
A third option I can think of is using a finite state machine. I have heard a little about them, but I'm sure if that will help me in this case or not.
What is the recommended design pattern for my problem?
I understand the dilemma you are running into. When I first started iOS I had a very hard time wrapping my head around relinquishing control to and from the operating system.
In general iOS would encourage you to go with method A. Usually you have variables in your ViewController which are set in method A(), and then they are checked in CompleteA() to verify that A() ran first etc.
Regarding your question about Finite State Machines, I think that it may help you solve your problem. The very first thing I wrote in iOS was a FSM (there for this is pretty bad code) however you can take a look here (near the bottom of FlipsideViewController.m:
https://github.com/esromneb/ios-finite-state-machine
The general idea is that you put this in your .h file inside an #interface block
static int state = 0;
static int running = 0;
And in your .m you have this:
- (void) tick {
switch (state) {
case 0:
//this case only runs once for the fsm, so setup one time initializations
// next state
state = 1;
break;
case 1:
navBarStatus.topItem.title = #"Connecting...";
state = 2;
break;
case 2:
// if something happend we move on, if not we wait in the connecting stage
if( something )
state = 3;
else
state = 1;
break;
case 3:
// respond to something
// next state
state = 4;
break;
case 4:
// wait for user interaction
navBarStatus.topItem.title = #"Press a button!";
state = 4;
globalCommand = userInput;
// if user did something
if( globalCommand != 0 )
{
// go to state to consume user interaction
state = 5;
}
break;
case 5:
if( globalCommand == 6 )
{
// respond to command #6
}
if( globalCommand == 7 )
{
// respond to command #7
}
// go back and wait for user input
state = 4;
break;
default:
state = 0;
break;
}
if( running )
{
[self performSelector:#selector(tick) withObject:nil afterDelay:0.1];
}
}
In this example (modified from the one on github) globalCommand is an int representing the user's input. If globalCommand is 0, then the FSM just spins in state 4 until globalCommand is non zero.
To start the FSM, simply set running to 1 and call [self tick] from the viewController. The FSM will "tick" every 0.1 seconds until running is set to 0.
In my original FSM design I had to respond to user input AND network input from a windows computer running it's own software. In my design the windows PC was also running a similar but different FSM. For this design, I built two FIFO queue objects of commands using an NSMutuableArray. User interactions and network packet would enqueue commands into the queues, while the FSM would dequeue items and respond to them. I ended up using https://github.com/esromneb/ios-queue-object for the queues.
Please comment if you need any clarification.
Hello I am trying to create a please wait screen.This screen will appear when my program requests data from web service and will hide when the process is finished.Also I want to add a time out if request process lasts longer than 90 seconds.
can anyone help or show me a guiding example about that matter.
public static void showBusyDialog() {
try
{
if (busyDialog == null) {
busyDialog = new Dialog("Please Wait", null, null, 0, Bitmap.getPredefinedBitmap(Bitmap.HOURGLASS));
busyDialog.setEscapeEnabled(false);
}
synchronized (Application.getEventLock()) {
busyDialog.show();
}
}
catch(Exception e)
{
}
}
and my hiding code is
public static void hideBusyDialog() {
try
{
if (busyDialog == null) {
// busyDialog = new Dialog("Please wait...", null, null, 0, Bitmap.getPredefinedBitmap(Bitmap.HOURGLASS));
busyDialog.setEscapeEnabled(false);
}
synchronized (Application.getEventLock()) {
busyDialog.close();
}
}catch(Exception e)
{
}
}
Many BlackBerry® smartphone applications need to wait for some network activity (or another blocking operation, which must process in the background), while still holding up the User Interface (UI) and displaying a progress indicator.
You can follow through this links
Links
Sample "Please Wait" screen - part 1
Sample "Please Wait" screen - part 2
Sample "Please Wait" screen - part 4
you can download simple examples for Please wait screen
PleaseWait1.zip 25 KB
PleaseWait2.zip 25 KB
PleaseWait3.zip 25 KB
Note :in case above Links not working then just follow following contents
There seem to be two common issues when programming this:
1) As applications are not allowed to block the Event Thread, how do they get the UI processing to wait?
2)How can the background Thread update the UI?
This article is intended to help with these issues and provide a fully functioning "Please Wait" sample Popup Screen. However, as there is quite a lot to explain, in this first article, we will just create a popup screen that will show itself, hold up the UI, and then remove itself once the background processing has finished. This does not give us any progress indication, nor does it let the user cancel the wait. These points will be covered in a followup article. But the code supplied with this article will be useful anyway, especially when the duration of the background processing is not known and the user may not cancel the processing.
First, we start with the background processing we need to run. While this could be anything, typically this will be network processing, like the following:
httpConn = (HttpConnection)Connector.open(_url + ";deviceside=true");
responseCode = httpConn.getResponseCode();
responseMessage = "Response Code: " + Integer.toString(responseCode);
To initiate this network processing, we have a MainScreen that contains
1) A BasicEditField that allows the entry of a URL
2) A RichTextField that should display the response code (or error message). Here are the important parts of that screen:
BasicEditField _requestedURLField = new BasicEditField("http://", "www.blackberry.com", 255, BasicEditField.FILTER_URL);
RichTextField _responseField = new RichTextField("<response code>", RichTextField.NON_FOCUSABLE);
We would like the MainScreen to be updated with the result. As noted above, background processing can't directly update the UI; UI updating code must be on the Event Thread. There are several ways to get a background process onto the Event Thread, see the related article for more. In this case, we will use the following code:
// Make things final so we can use them in the inner class
final String textString = responseMessage;
final RichTextField rtf = _resultField;
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
rtf.setText(textString);
}
});
Now we must define the PleaseWaitPopupScreen to be displayed while waiting.
To give the user something to look at while they are waiting, we have an animated .gif, which is diplayed using the code in the AnimatedGIFField (see related link). And, so the user knows what they are waiting for, the PleaseWaitPopupScreen is supplied with a String to display, as the following constructor shows:
private PleaseWaitPopupScreen(String text) {
super(new VerticalFieldManager(VerticalFieldManager.VERTICAL_SCROLL | VerticalFieldManager.VERTICAL_SCROLLBAR));
GIFEncodedImage ourAnimation = (GIFEncodedImage) GIFEncodedImage.getEncodedImageResource("cycle.agif");
_ourAnimation = new AnimatedGIFField(ourAnimation, Field.FIELD_HCENTER);
this.add(_ourAnimation);
_ourLabelField = new LabelField(text, Field.FIELD_HCENTER);
this.add(_ourLabelField);
}
PleaseWaitPopupScreen provides a method – showScreenAndWait(..) – which will create and display the Popup screen, run the Background processing, and then dismiss the Popup screen.
The final piece of the puzzle involves supplying showScreenAndWait(..) with the processing to run.
Java has the concept of a Runnable, which is an Object that contains a public void run() method that should be executed. In this case, we have the Connection code and screen update code, given above, that should be executed. So, this code is packaged up into a new Runnable Object, which is supplied to showScreenAndWait(..). And here is that method. Note how a new Thread is created and run.
public static void showScreenAndWait(final Runnable runThis, String text) {
final PleaseWaitPopupScreen thisScreen = new PleaseWaitPopupScreen(text);
Thread threadToRun = new Thread() {
public void run() {
// First, display this screen
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
UiApplication.getUiApplication().pushScreen(thisScreen);
}
});
// Now run the code that must be executed in the Background
try {
runThis.run();
} catch (Throwable t) {
t.printStackTrace();
throw new RuntimeException("Exception detected while waiting: " + t.toString());
}
// Now dismiss this screen
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
UiApplication.getUiApplication().popScreen(thisScreen);
}
});
}
};
threadToRun.start();
}
And this is the key part of the PleaseWaitPopupScreen. Note how this code will create and display a Popup screen to the user, including an animated icon, while it is running the background processing. Input from the user is blocked by the Popup screen until the processing completes. The originating screen is updated as a result of the background processing.
Download the associated .zip archive, which contains the source included in this article.
In the next article, we will extend this code to be able to handle:
a) Status updates from the Background Thread
b) "Time to go" indication
c) Being cancelled by the BlackBerry smartphone user
Just put timer after you show busy dialog.
showBusyDialog();
Timer timer = new Timer();
TimerTask task = new TimerTask() {
public void run() {
hideBusyDialog();
}
};
timer.schedule(task, 9000);
this is for time out. If the process finishes less than 90 seconds you should call
timer.cancel();
timer = null;
task = null;
For my Blackberry application I am using a start up screen with progress bar. I am filling the progress bar using a timer and after the progress bar is complete, I need to navigate to another screen.
I am checking like this, where 'i' is time, increasing from 0 to 100.
timer.cancel();
if(i>=99)
UiApplication.getUiApplication().pushScreen(new TipCalculatorScreen());
This code is not working.
For progress bar I am using code like this:
private GaugeField percentGauge;
percentGauge = new GaugeField(null, 0, 100,50, GaugeField.PERCENT);
timer=new Timer();
timer.scheduleAtFixedRate(new TimerTask(){
int i=0;
public void run() {
percentGauge.setValue(i);
i++;
if(i>=99)
{
timer.cancel();
//for page navigating i am given like this here screen is not navigating getting error
UiApplication.getUiApplication().pushScreen(new nextscreen());
}
}
}, 100,100);
You need to make changes to the UI on the UI thread. The TimerTask is executing on its own thread. Instead of
UiApplication.getUiApplication().pushScreen(new nextscreen());
you should use
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
UiApplication.getUiApplication()..pushScreen(new nextscreen());
}
});
The update to your gauge control probably needs the same treatment.
I'm getting some strange behaviour in the start-up of a Windows app and wondered if anyone could throw any light on what is happening and how to get around it.
The problem is with the start-up of the app - it should show a splash screen then a login form. The code for this is:
[STAThread]
static void Main()
{
Application.ThreadException += Application_ThreadException;
MainForm mainForm = null;
Thread splashThread = new Thread(ShowSplash);
try
{
// set up app
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
// Splash screen
Splash splash = new Splash();
splashThread.Start(splash);
// enable logging
log4net.Config.XmlConfigurator.Configure();
// Create main form
mainForm = new MainForm();
// kill splash
HideForm(splash);
splashThread.Abort();
}
catch (Exception e)
{
splashThread.Abort();
MessageBox.Show(e.Message, "An exception occurred: ", MessageBoxButtons.OK, MessageBoxIcon.Error);
Environment.Exit(0);
}
// start
Login login = new Login();
login.Show();
if (!mainForm.IsDisposed)
{
Application.Run(mainForm);
}
}
static void ShowSplash(object splash)
{
if (!(splash is Splash))
throw new ArgumentException("Splash screen is of wrong type.");
Splash splashForm = (Splash) splash;
splashForm.ShowDialog();
}
// Thread safe hide form
private delegate void HideFormCallback(Form form);
private static void HideForm(Form form)
{
if (form == null || form.IsDisposed)
return;
if (form.InvokeRequired)
{
HideFormCallback d = HideForm;
form.Invoke(d, new object[] { form });
}
else
{
form.Hide();
}
}
So, we're starting up a new thread with the splash screen, setting up the rest of the app in the meantime, then killing the splash screen just before showing the login form.
The problem I'm having is that the login form doesn't have focus when the app starts. The splash screen pops up and goes away as expected. The login form pops up in front of any open windows but doesn't have focus - the folder containing the executable (that I double-clicked to launch) still has focus even when it's behind the login form.
If I comment out all the lines to do with the splash screen, the login form has focus when it appears.
My guess would be that the focus reverts back to the executable folder when the splash screen is hidden but I don't know why the login form doesn't get focus when it launches.
Calling .Focus() on the login form returns null so doesn't work.
Neither form have TopMost or such set on them.
If anyone has any suggestions for what's going on, it would be much appreciated.
This is what I've ended up doing as a somewhat hacky fix:
void LoginView_Shown(object sender, EventArgs e)
{
SetForegroundWindow(Handle);
this.BringToFront();
Activate();
}
[DllImport("user32")]
public static extern int SetForegroundWindow(IntPtr hwnd);