Im wondering how to implement undo redo functionality with a TextArea. I already have an undoredo framework functionality working, now I have two questions.
When do I start/stop a new undo/redo command, eg when a user hits undo, how far back do I go.
How do I implement this(1.) in a normal TextArea
My thinking:
I thinking that I should create a new undo command, when anything but a alphanumber+space is hit. To do this I would use the keyDown event and test if the key is alpha num if it is not I will reset the command.
Sound good?
Listening for keydown events would miss any text editing that user does with the mouse (cut/copy/paste).
I think a better approach would be to listen for 'change' event on the control (which fires whenever the content changes through user input), and just push the full content of the control (its 'text' or 'htmlText' attribute) with every change event into a undo-buffer (an Array of Strings). I assume that the memory usage is not an issue (it probably isn't, depending on the expected size of the controls content and number of undo levels).
This way, you implement undo/redo just by copying the corresponding control state (moving up and down through array, basically) in the undo buffer back into the control.
The 'proper' approach would be to track the actual edits, and would be condsiderably more complicated.
1.When do I start/stop a new undo/redo command, eg when a user hits undo, how far back do I go.
Do you think your users will need to undo multiple steps? If so, then you may want to have a history (e.g. Paint .NET) and allow infinite undo-s. Otherwise, just remember the most recently performed action.
1.) You should listen for the Event.CHANGE event on the TextField and create a history step each time the event is fired. A history step consists in your case of two values: old and new.
Old is the value of the TextField before change, new is its value after the change.
2.) Your history is a sequence of actions or you can use the Memento Pattern. I think actions are much easier to use. A history action has two methods, undo() and redo(). So in undo() you have to say textField.text = oldContent and in the redo() method you say textField.text = newContent. Your history will also need a pointer to the current action.
3.) To make it a little bit better. You should not listen only for Event.CHANGE but instead listen for the first CHANGE and then the next FOCUS_OUT for that TextField. In that case, a history step is only created once I stop editing the TextField. But it depends on your TextField and how you want to distribute history steps. A multiline TextField should not create a history step only on FOCUS_OUT :)
Related
I may have worked myself into a corner but this sounded to me like a good idea at the time.
I have been developing an interface that permits a user to modify settings of a robotic device, i.e. speed, directions, force, etc. with a very large series of options in the form of ComboBoxes. The problem is that there are about a thousand of these things, in sub categories. e.g. Speed category x1, x2, x3, Y1, y2, etc. So rather than create a thousand comboboxes in QT, I thought the good idea was to create one set of 50 (ish) and then provide a few button to switch between categories. So when the user selects speed QT, populates the comboboxes with the appropriate options, sets the style sheets and text for the labels etc. So it appears as though a dedicated page exists. Then if the user selects Direction, QT Writes the current index of each box to a dedicated array and then repopulates the boxes, labels etc with the appropriate content. I then do this over and over for the various needs of the system.
All of that seems to work fine. However I am now in a bind where the options provided to navigate to each page have grown. For instance I have forward / backward buttons (like you woudl expect in a set-up wizard), as well as action menus at the top to jump to a page. So now the code is becoming very repetitious. If you select the next button, I write the current values to array, then repopulate. If you jump to the page from anywhere, I look to see where I am, write it to array, and populate the boxes. Thus if I need to change anything I have to make the change in numerous places in the code.
I know that this is not optimal. What I woudl like to do is run a continuous loop as I woudl normally do with Micros in C. So the program can look at a variable in each pass and if it is then it does. I am not however skilled enough to figure this loop out in QT. So my new thought was...
Is it possible to trigger an action or slot with a variable. For example, if the user presses the Next button it triggers a slot for a button that does not exist, so that QT will execute a particular line of Code? Then I can have 1 dedicated section focused on reading and writing boxes, with a bunch of actions that will take me there.
You can make a signal that is triggered with an emit call in your code, so you'd hook up the next button signal of clicked to a slot that does some work and moves on, or directly calls another signal that you've created that triggers a slot elsewhere, or do some work in a lambda triggered by the button press.
I would first load all the ComboBoxes options in a QStringList array (or maybe an array of QList<QLatin1String> lists - for memory saving and code efficiency).
Then I would keep an array of a 1000 integers for current ComboBox indexes.
When the user changes a value in some ComboBox, the currentIndexChanged signal will trigger the corresponding slot (a single slot for all the ComboBoxes would be enough - sender()->objectName() to get the name of the ComboBox which had sent the signal):
void WindowWidget::on_ComboBox_currentIndexChanged(int index)
{
name = sender()->objectName();
/* here change the corresponding integer in the current
indexes array */
}
On Next/Back button push repopulate the ComboBoxes. Also, provide some 'Save' button for saving the ComboBoxes indexes (or trigger the Save slot on some action, i.e. on window close either even on a timer signal).
I am subclassing QDoubleSpinBox to add some features (like incrementing the value based on the location of the cursor in the lineedit) and to change some features I find annoying. One of the latter is that intermediate values are emitted: e.g. if you want to enter the value 323 it will emit 3 then 32 then finally 323. I'd like to set it to only emit on entry (i.e. only actually change value on entry).
Anyway, I can't figure out how to capture these intermediate edits. I overrode setValue to see if I could stop it there somehow, but it apparently isn't called (or at least my override isn't). I'm not sure how the value is actually getting set while editing in line edit.
More generally, the logic of this box escapes me. Is there some documentation that explains e.g. "if you type a digit into the lineedit then this series of routines is called... while if you hit the up arrow, this series of routines is called?"
In case it matters, I'm using PyQt5
EDIT: Here is another case in which having access to this is important. Say I want to implement an undo/redo structure for the box. The only way I can think of to get access to the changed values is to connect to the valueChanged signal. But if I'm subclassing the box it seems a little convoluted to listen for a signal rather than just watch the value change 'internally' Or am I missing something here?
You could use the following signal:
void QAbstractSpinBox::editingFinished() [signal]
This signal is emitted editing is finished. This happens when the spinbox loses focus and when enter is pressed.
based on the documentation of QAbstractSpinBox:
http://qt-project.org/doc/qt-5.1/qtwidgets/qabstractspinbox.html#editingFinished
There is nothing that combines the arrow based changes and the editingFinished changes.
My use case was to let the user enter the value without getting the signal on each new digit, while still making ↑, ↓, Page Up, Page Down keys and arrow buttons work as usual, emitting the signal on each activation.
QAbstractSpinBox::editingFinished signal doesn't provide this functionality: it's only ever emitted when focus is lost or Return/Enter is pressed.
What does work exactly as I need is the keyboardTracking property of QAbstractSpinBox. If it's true (the default), the spinbox emits valueChanged on each digit typed. If you set it to false, it behaves exactly as I described in the beginning of this answer.
How can I refresh view after a certain event?
I have a view which contains multiple groups. I want to show or hide some groups.
onCreationComplete() or initialize() method works only at the beginning of the view creation.
Try invalidateDisplayList() on the view
Let me know if that doesn't do the trick and we'll try some other tricks.
I personally don't like the answer that says to call invalidateDisplayList (sorry no offense Nate nothing personal). I feel it's too vague and doesn't explain what this does under the hood and furthermore you shouldn't have to call it directly in cases such as the one explained in the OPs question. You can simply create booleans that are bindable for each of the groups you'd like to show/hide then in the event handler set those booleans to the appropriate value and if they are bound to the visible and include in layout properties of the containers those containers will internally call invalidateDisplayList after calling set visible and consequently commitProperties.
This is basically what happens under the hood as I understand it: The way this works is values aren't committed or used to update the display until the next frame this way it doesn't get bogged down doing unnecessary layout calculations. So you update the bindable property which fires an event which triggers a notification in the listener (in this case a function that sets the property on your control), that in turn passes along the value to the control which sets an internal flag to update the property and calls invalidateProperties. When it hits the next frame redraw it sees that the properties flag is dirty (true) and then calls commitProperties, this computes/sets the appropriate values (possibly also invalidating then "fixing" the size using invalidateSize() and measure()) and calls invalidateDisplayList, then during the same frame it sees that the display list flag is dirty so it calls updateDisplayList, here it uses the values of the properties to draw appropriately.
You should also be able to achieve this using states, which add or remove children from the display list based on an array of "actions" for each state.
I'm writing a wizard UI based on the QWizard Qt object. There's one particular situation where I want the user to log in to a service using host, username, and password. The rest of the wizard then manipulates this service to do various setup tasks. The login may take a while, especially in error cases where the DNS name takes a long time to resolve -- or perhaps it may not even resolve at all.
So my idea is to make all three fields mandatory using the registerField mechanism, and when the user hits Next, we show a little throbber on the wizard page saying "Connecting to server, please wait..." while we try to connect in the background. If the connection succeeds, we advance to the next page. If not, we highlight the offending field and ask the user to try again.
However, I'm at a loss for how to accomplish this. The options I've thought of:
1) Override validatePage and have it start a thread in the background. Enter a wait inside validatePage() that pumps the Qt event loop until the thread finishes. You'd think this was the ugliest solution, but...
2) Hide the real Next button and add a custom Next button that, when clicked, dispatches my long running function in a thread and waits for a 'validation complete' signal to be raised by something. When that happens, we manually call QWizard::next() (and we completely bypass the real validation logic from validatePage and friends.) This is even uglier, but moves the ugliness to a different level that may make development easier.
Surely there's a better way?
It's not as visually appealing, but you could add a connecting page, and move to that page. If the connection succeeds, call next() on the wizard, and if the connection fails, call previous() and highlight the appropriate fields. It has the advantage of being relatively straightforward to code.
My final choice was #2 (override the Next button, simulate its behavior, but capture its click events manually and do the things I want to with it.) Writing the glue to define the Next button's behavior was minimal, and I was able to subclass QWizardPage with a number of hooks that let me run my task ON the same page, instead of having to switch to an interstitial page and worry about whether to go forwards or backwards. Thanks Caleb for your answer though.
I know this has already been answered (a long time ago!) but in case anyone else is having the same challenge. Another method for this is to create a QLineEdit, initiate it as empty and set it as a mandatory registered field. This will mean that "Next" is not enabled until it is filled with some text.
Run your connection task as normal and when it completes use setText to update the QLineEdit to "True" or "Logged in" or anything other than empty. This will then mean the built in isComplete function will be passed as this previously missing mandatory field is now complete. If you never add it to the layout then it won't be seen and the user won't be able to interact with it.
As an example ...
self.validated_field = QLineEdit("")
self.registerField('validated*', self.validated_field)
and then when your login process completes successfully
self.validated_field.setText("True")
This should do it and is very lightweight. Be sure though that you consider the scenario where a user then goes back to that page and whether you need to reset the field to blank. If that's the case then just add in the initialisePage() function to set it back to blank
self.validated_field.setText("")
Thinking about it you could also add the line edit to the display and disable it so that a user cannot update it and then give it a meaningful completion message to act as a status update...
self.validated_field = QLineEdit("")
self.validated_field.setDisabled(True)
self.validated_field.setStyleSheet("border:0;background-color:none")
self.main_layout.addWidget(self.validated_field)
self.registerField('validated*', self.validated_field)
and then when you update it..
self.validated_field.setText("Logged in")
My TileList has allowMultipleSelection on. I am using itemClick to call a function. I can use listEvent.currentTarget.selectedItem to determine what object was just clicked on if I am selecting, but when I ctrl + click to deselect an item, it automatically selects something else in the TileList, thus changing the selectedItem. It seems like ctrl + clicking to deselect changes the target before the itemClick function is run. Is there a way to figure out what was just deselected?
I can use selectedItems to get the same end functionality I need. However, I am concerned about performance when the selectedItems collection gets really long. We are using blazeds to send the data back and forth and it would be much faster if we sent the one item that was added/removed then the whole thing each time.
I'm a bit surprised that you seem to be saying that "itemClick" isn't being dispatched in each case. I wonder if you should try listening to the "change" event instead?
What about adding a property called "previouslySelectedItems" and doing a comparison between that and "selectedItems" to figure out what changed? After the comparison is done, set previouslySelectedItems = selectedItems.