I am coding a program combining QML and C++. The TableView shows a column of a table. I can add or delete the record correctly, but I can not update the TableView, which always shows the content before adding or deleting.
How to update theTableView?
PS: I do not know whether it is good choice to code with QML and C++ instead of QWidget directly.
main()
{
//other code
......
MySqlModel *model = new MySqlModel;//class MySqlModel : public QSqlTableModel
model->QSqlQueryModel::setQuery("SELECT FieldName1 FROM Table");
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty ("SQQL", model);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
//other code
......
}
In the qml:
TableView{
//other code
......
model: SQQL
//other code
......
}
QWidget-based has more default feature built-in, I would suggest you start from there.
how to enable edit
override flags function to enable edit on items, see
http://www.qtcentre.org/threads/38338-Can-t-edit-my-QTableView-cells
http://doc.qt.io/qt-4.8/qabstractitemview.html#EditTrigger-enum
how to sync changes back to db
you could manual commit the change per edit, or manually batch all changes in a db transaction, or you could just use sqltablemodel
http://doc.qt.io/qt-4.8/qsqltablemodel.html#EditStrategy-enum
However, if you need more flexible ui, or it is for a multi-touch device, you should go QML approach
make a qabstractview model
have qml view that bind to this qabstracttableview model. or using qt control tool kits
Related
I would like to have one kotlin file with the logic and I would like to allow users to switch between two different XLM layouts (logic of program is still the same, but layout of buttons shall be changed when clicking on button).
I simply add setContentView function to setOnClickListener for this button in order to load activity_main_second_layout.xml layout.
PS. activity_main_second_layout.xml is almost the same like activity_main.xml, I only changed the position of elements (not the names of elements)
button_switch_to_the_second_design.setOnClickListener {
setContentView(R.layout.activity_main_second_layout);
}
When clicking on the button, voala, the layout really changes to the second one.
BUT the functionality of the program is not working any more, the logic disappear. It seems that I need to resume running of the program somehow to make the code working again without interuption including loss of variables.
There is a lot of ways to do that.
In my opinion you should not try to change layout in runtime - it's possible, but you have to override setContentView and rebind all views and all listeners (or do it in other method, which will be called after changing the layout).
So... Sth like this:
fun sth() {
setContentView(R.layout.activity_main_second_layout)
rebindLayout(R.layout.activity_main_second_layout)
}
fun rebindLayout(#LayoutRes layoutId: Int) {
when (layoutId) {
R.layout.activity_main_first_layout -> { /* rebind views here */ }
R.layout.activity_main_second_layout -> { /* rebind views here */ }
}
}
The other's, better I think is to create independent fragments and change fragment via fragmentManager.
Others approches - ViewAnimator, ViewSwitcher.
I run often into many problems which leads to refactoring my code...
That is why I want to ask for some recommendations.
The problems I'm running into are:
1) Providing data to XAML
Providing simple data to control value instead of using a value converter. For instance I have a color string like "#FF234243" which is stored in a class. The value for the string is provided by a web application so I can only specify it at runtime.
2) UI for every resolution
In the beginnings of my learning I got told that you can create a UI for every possible resolution, which is stupid.
So I've written a ValueConverter which I bind on an element and as ConverterParameter I give a value like '300' which gets calculated for every possible resolution... But this leads to code like this...
<TextBlock
Height={Binding Converter={StaticResource SizeValue}, ConverterParameter='300'}
/>
3) DependencyProperties vs. NotifyProperties(Properties which implement INotifyPropertyChanged) vs. Properties
I have written a control which takes a list of value and converts them into Buttons which are clickable in the UI. So I did it like this I created a variable which I set as DataContext for this specific Control and validate my data with DataContextChanged but my coworker mentioned that for this reason DependencyProperties where introduced. So I created a DependecyProperty which takes the list of items BUT when the property gets a value I have to render the buttons... So I would have to do something like
public List<string> Buttons
{
get { return (List<string>)GetValue(ButtonsProperty); }
set
{
SetValue(ButtonsProperty, value);
RenderButtons();
}
}
// Using a DependencyProperty as the backing store for Buttons. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ButtonsProperty =
DependencyProperty.Register("Buttons", typeof(List<string>), typeof(MainPage), new PropertyMetadata(""));
private void RenderButtons()
{
ButtonBar.Children.Clear();
ButtonBar.ColumnDefinitions.Clear();
if(Buttons != null)
{
int added = 0;
foreach (var item in Buttons)
{
var cd = new ColumnDefinition() { Width = new GridLength(1, GridUnitType.Star) };
var btn = new Button() { Content = item };
ButtonBar.ColumnDefinitions.Add(cd);
ButtonBar.Children.Add(btn);
Grid.SetColumn(btn, added);
}
}
}
And have to use it like this:
<Controls:MyControl
x:Name="ButtonBar" Button="{Binding MyButtons}">
</Controls:MyControl>
Since these are a lot of topics I could seperate those but I think that this is a pretty common topic for beginners and I have not found a got explanation or anything else
1. Providing data to XAML
There are two options: prepare data in the ViewModel or to use converter.
To my mind using converter is better since you can have crossplatform viewModel with color like you mentioned in your example and converter will create platform dependent color. We had similar problem with image. On android it should be converted to Bitmap class, while on UWP it's converted to BitmapImage class. In the viewModel we have byte[].
2. UI for every resolution
You don't need to use converter, since Height is specified in effective pixels which will suit all the required resolutions automatically for you. More info can be found at the following link:
https://learn.microsoft.com/en-us/windows/uwp/design/layout/layouts-with-xaml
There are two options how to deal with textblock sizes:
a) Use predefined textblock styles and don't invent the wheel (which is the recommended option):
https://learn.microsoft.com/en-us/windows/uwp/design/style/typography#type-ramp
Or
b) Specify font size in pixels. They are not pixels, but effective pixels. They will be automatically scaled on different devices:
https://learn.microsoft.com/en-us/windows/uwp/design/style/typography#size-and-scaling
Furthermore, use adaptive layout to have different Layout for different screen sizes.
3) DependencyProperties vs. NotifyProperties(Properties which implement INotifyPropertyChanged) vs. Properties
As per your code you can try to use ListView or ItemsControl and define custom item template.
DependencyProperties are created in DependencyObject and are accessible in xaml. All controls are inherited from DependencyObjects. Usually you create them when you want to set them in xaml. They are not stored directly in the objects, but in the global dictionary and resolved at runtime.
DependencyProperties were created long time ago and you can find lots of links which explain them in details:
http://www.wpftutorial.net/dependencyproperties.html
https://techpunch.wordpress.com/2008/09/25/wpf-wf-what-is-a-dependency-property/
When should I use dependency properties in WPF?
What is a dependency property? What is its use?
What is a dependency property?
INotifyPropertyChanged INPC are the central part of MVVM. You bind your view to viewModel which implements INPC and when you change value of the property control is notified and rereads the new value.
Download the following video in high resolution which explains MVVM in details (by Laurent Bugnion):
https://channel9.msdn.com/Events/MIX/MIX11/OPN03
MVVM: Tutorial from start to finish?
Normal properties are used in model classes or when there is no need to notify UI regarding changes.
I'm new here!
I searched internet a lot for my question, but I didn't found anything - or I'm really thinking wrong.
I program on VB.NET since 2 years, and on XNA since 6 months. I built a game and an editor for the game, and they are running great.
The question i about my editor (for an RPG game), and I'll try to explain at my best.
I have a main form with menustrips on top and a big picturebox covering the entire form, a picbox that is binded to the Game1 object when it start with the command Run().
The Game1 object handles two classes, that are basically panels that it draws on the picbox of the main form: a tileset panel in the left down the tabpage, and a map panel on the right. This works perfectly.
The problem is when for the first time yesterday I tried to draw with XNA on a form. I have multiple forms to manage NPCs, equipment, conditions, events, variables, etc and in the event form, I have a tabpage that manages map teleport events. On this tabpage I have a list of maps and a picbox where I want to draw a small view of the selected map. For this, I created of course a minimap panel with it's own draw and update methods.
...but of course, the minimap appears on the main form on the normal map.
I tried to change in real time the DeviceWindowHandle, but I failed... apparently, it changes only during the Run()
I tried to create a new game object and binding him to the event teleport form, but in the moment of lunching the Run() of this object, the debugger stops saying that I cannot launch more that one game loop in a thread.
I can't believe that XNA doesn't let to draw multiple things on different forms... and I can not pause the main loop from the event form (which is called from the NPC form) to start the minimap loop!
I think that is something really easy that unfortunately I don't know...
I'm getting crazy and lost... what I can do?
Please help me, thanks!!
Here's an example of what I commented (Sorry it's in C# but I don't really write VB.Net. Translating it should be pretty straight forward though):
private MainGame mainGame;
private ToolboxGame toolbox1;
private ToolboxGame toolbox2;
// And this should be put in some Form Initialization method:
Task.Factory.StartNew(() => {
this.mainGame = new MainGame(imgEditorPictureBox.Handle)
this.mainGame.Run();
}
Task.Factory.StartNew(() => {
this.toolbox1 = new ToolboxGame(toolbox1PictureBox.Handle)
this.toolbox1.Run();
}
Task.Factory.StartNew(() => {
this.toolbox2 = new ToolboxGame(toolbox2PictureBox.Handle)
this.toolbox2.Run();
}
Something like that should do it. Obviously whenever you "move" variables from one "game" to another, keep in mind that they run on different threads, so anywhere you use it, you'll need to
lock (dummyObject)
{
// Use data
}
to make sure you're not accessing it in one game, while the other is trying to set it.
Locking in VB.Net: Is there a lock statement in VB.NET?
You'll obviously need to come up with some smart infrastructure to get this working smoothly, but since you've made a game and editor before, I'm sure this should not prove a humongous challenge.
All you want show to the player you need draw in the game window. You have one Game with one GraphicsDevice and by default all you draw will be rendered on the game window. But you can call GraphicsDevice.SetRenderTarget method to change render target. Call it with RenderTarget2D object as parameter and anithing you will draw after this will be rendered to that render target.
Next you need call GraphicsDevice.SetRenderTarget(null) to set game window as render target again.
There is my (uncompleted yet) custom GUI realization for XNA. I hope it can help you.
Update
class Game1 : Game
{
GraphicsDevice graphicsDevice;
SpriteBatch spriteBatch;
public RenderTarget2D MinimapRenderBuffer;
public RenderTarget2D AnotherRenderBuffer1;
public RenderTarget2D AnotherRenderBuffer2;
public EventHandler RenderBuffersUpdated;
void Initialize()
{
// Better initialize them only once, don't do it in Draw method
this.MinimapRenderBuffer = new RenderTarget2D(this.graphicsDevice, 100, 100); // any size you want
this.AnotherRenderBuffer1 = new RenderTarget2D(this.graphicsDevice, 50, 50);
this.AnotherRenderBuffer2 = new RenderTarget2D(this.graphicsDevice, 500, 500);
}
void Draw()
{
this.graphicsDevice.SetRenderTarget(this.MinimapRenderBuffer);
// draw minimap to MinimapRenderBuffer
this.graphicsDevice.SetRenderTarget(this.AnotherRenderBuffer1);
// draw whatewer to AnotherRenderBuffer1
this.graphicsDevice.SetRenderTarget(this.AnotherRenderBuffer2);
// draw whatewer to AnotherRenderBuffer2
this.graphicsDevice.SetRenderTarget(null);
// now draw to screen
if (this.RenderBuffersUpdated != null)
{
RenderBuffersUpdated(null, null);
}
}
}
And use rendertargets in your editor when event raised. And you can convert them to bitmaps.
I have a costum editor for my own languages and I want to change from the property menu between them and recolor the syntax accordingly. I don't know if I have to use a reconciler or something else. The only way that the syntax is recolored, is by closing and opening the current file.
In your editor you need to listen for property change events from your preference store.
In your initializeEditor method call setPreferenceStore(preferenceStore)
Override the handlePreferenceStoreChanged method:
#Override
protected void handlePreferenceStoreChanged(PropertyChangeEvent event)
{
// TODO update settings affected by the event
// TODO If required invalidate the current presentation to update the colors
getSourceViewer().invalidateTextPresentation();
super.handlePreferenceStoreChanged(event);
}
You need to add code to look at the property change event to see if it is one that you need to handle. If the event changes something (such as changing the colors) that needs to text to be redrawn call getSourceViewer().invalidateTextPresentation().
To support all the normal text editor preferences you need to use a chained preference store in the setPreferenceStore call:
IPreferenceStore generalTextStore = EditorsUI.getPreferenceStore();
IPreferenceStore yourPreferenceStore = get your preference store
IPreferenceStore combinedPreferenceStore = new ChainedPreferenceStore(new IPreferenceStore[] {yourPreferenceStore, generalTextStore});
setPreferenceStore(combinedPreferenceStore);
I Build a scrollViewer and its elements in my ViewModel, and it's built into a property FrameworkElement PageElement I rebuild the pageElement every time some event happens, I want to bind the PageElement to a real scrollViewer in the View so that whenever I change pageElement, it draws itself in it's view.
Let me give you a little armchair advice. I don't know the details of your project but the details in your question make me draw a few conclusions.
First, to have your view model create UI elements is not wrong. But it is really unusual. It sounds like you might be missing the concept of data template or data template selector.
Using a data template allows you to have a rich presentation of data that is built as the individual record is generated and rendered in a repeater or in a single content control.
Using a data template selector allows you to have various different presentations of data that using code-behind logic will switch between based on data or other criteria.
Ref on templates: http://blog.jerrynixon.com/2012/08/windows-8-beauty-tip-using.html
Second, to have your UI be re-generated as the result of an event being raised sounds like a short path to performance problems.
Every time you manually create elements and add them to the visual tree, you put your app at risk of binding lag while the layout is re-rendered. Run your app on an ARM and I bet you may already see it. Then again, a simplistic UI may not suffer from this general rule of thumb.
Because I do not know the event, I cannot presume it is frequently occurring. However, if it is frequently occurring, then even a simplistic UI will suffer from this.
Now to answer your question
Sherif, there is no write-enabled property on a scrollviewer that will set the horizontal or vertical offset. The only way to set the offset of a scrollviewer is to call changeview().
var s = new ScrollViewer();
s.ChangeView(0, 100, 0);
You cannot bind to a method, so binding to something like this is a non-starter without some code-behind to read the desired offset and calling the method directly.
Something like this:
public sealed partial class MainPage : Page
{
MyViewModel _Vm = new MyViewModel();
ScrollViewer _S = new ScrollViewer();
public MainPage()
{
this.InitializeComponent();
this._Vm.PropertyChanged += (s, e) =>
{
if (e.PropertyName.Equals("Offset"))
_S.ChangeView(0, _Vm.Offset, 0);
};
}
}
public class MyViewModel : INotifyPropertyChanged
{
private int _Offset;
public int Offset
{
get { return _Offset; }
set
{
_Offset = value;
PropertyChanged(this, new PropertyChangedEventArgs("Offset"));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
But let me caution you. The offset will need to be based on something. And those variables may change based on the window size, the font size, scaling from transforms, and lots of other factors. The code above will work most of the time, but it will possible fail frequently on other devices.
So, what to do? My recommendation is that you code this in your code-behind, monitoring for whatever scenario you feel would require a scroll, and simply programmatically scroll it from bode-behind. Beware, though, programmatically scrolling a scrollviewer could make your UI confusing to the user.
You know your app. You will have to choose.
Best of luck!