I'm trying launch a simple JFace Tree.
It's acting really strange however. When I setInput() to be a single String, the tree opens up completely blank. However, when I set input to be a String array, it works great.
This has nothing to do with the LabelProvider or ContentProvider since these behave the same no matter what (it's a really simple experimental program).
setInput() is officially allowed to take any Object. I am confused why it will not take a String, and knowing why may help me solve my other problems in life.
Setting a single String as input:
TreeViewer treeViewerLeft = new TreeViewer(shell, SWT.SINGLE);
treeViewerLeft.setLabelProvider(new TestLabelProvider());
treeViewerLeft.setContentProvider(new TestCompareContentProvider());
treeViewerLeft.expandAll();
treeViewerLeft.setInput(new String("Stooge"));
Setting an array of Strings:
TreeViewer treeViewerLeft = new TreeViewer(shell, SWT.SINGLE);
treeViewerLeft.setLabelProvider(new TestLabelProvider());
treeViewerLeft.setContentProvider(new TestCompareContentProvider());
treeViewerLeft.expandAll();
treeViewerLeft.setInput(new String[]{"Moe", "Larry", "Curly"});
The second works, and launches a tree using the following providers:
public class TestCompareContentProvider extends ArrayContentProvider implements ITreeContentProvider {
public static int children = 0;
public Object[] getChildren(Object parentElement) {
children++;
if (children > 20){
return null;
}
return new String[] {"Moe", "Larry", "Curly"};
}
public Object getParent(Object element) {
return "Parent";
}
public boolean hasChildren(Object element) {
if (children >20){
return false;
}
return true;
}
}
and
public class TestLabelProvider extends LabelProvider {
public String getText(Object element){
return "I'm something";
}
public Image getImage(Object element){
return null;
}
}
You've inherited getElements from the ArrayContentProvider and that only works with arrays. You should override this method.
I don't think you need to extend ArrayContentProvider at all.
Related
Record is a new feature in c#9, Net 5
It's said
If you want the whole object to be immutable and behave like a value, then you should consider declaring it as a record
Creating a record in c#9 , NET 5:
public record Rectangle
{
public int Width { get; init; }
public int Height { get; init; }
}
Then instantiating it:
var rectangle = new Rectangle (20,30);
Trying to change the value:
rectange.Width=50; //compiler error
Compiler raise the error:
error CS8852: Init-only property or indexer 'Rectangle.Width' can only be assigned in an object initializer, or on 'this' or 'base' in an instance constructor or an 'init' accessor.
That is right and insure that the record is immutable.
Using a method like to test IsImmutable type give false, because in record there is no generated readonly properties.
How to check the record in c# 9, Net 5 is immutable at runtime or even it has init property?
A record is indeed mutable at runtime. This is intentional, is it means most serializer frameworks work without updating.
It is however possible to check if a property is initonly by checking:
public static bool IsInitOnly(PropertyInfo propertyInfo)
{
return propertyInfo?.SetMethod.ReturnParameter
.GetRequiredCustomModifiers()
.Any(x => x.FullName == _isExternalInitName)
?? false;
}
private static string _isExternalInitName =
typeof(System.Runtime.CompilerServices.IsExternalInit).FullName;
I don't think that it's possible to check for immutability at runtime.
Here's some of the generated code for your record. You can see that both properties have a public setter.
public class Rectangle : IEquatable<Rectangle>
{
[CompilerGenerated]
private readonly int <Width>k__BackingField;
[CompilerGenerated]
private readonly int <Height>k__BackingField;
protected virtual Type EqualityContract
{
[CompilerGenerated]
get
{
return typeof(Rectangle);
}
}
public int Width
{
[CompilerGenerated]
get
{
return <Width>k__BackingField;
}
[CompilerGenerated]
set
{
<Width>k__BackingField = value;
}
}
public int Height
{
[CompilerGenerated]
get
{
return <Height>k__BackingField;
}
[CompilerGenerated]
set
{
<Height>k__BackingField = value;
}
}
The following code will compile and run without errors.
var rect = new Rectangle { Height = 1, Width = 2 };
typeof(Rectangle).GetProperty("Height").SetValue(rect, 5);
Console.Write(rect.Height);
//Prints 5
At runtime the init accessor is just a regular setter. It's only at compile time that a check is made to only allow init accessor to be called during object initialization.
So I don't see any way to check at runtime that Rectangle is immutable.
I need to implement the search bar in navigation bar for android in xamarin.forms,while searching i found many examples for ios but not for android.How to achieve this for android through customrenderer?
Easy way to create a Search is to create class and make use of Filter options
like this
Search Bar Button on Top
<item android:id="#+id/action_search"
android:title="Search"
app:actionViewClass="androidx.appcompat.widget.SearchView"
app:showAsAction="always" />
Classes You May Require
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_menu, menu);
MenuItem searchItem = menu.findItem(R.id.action_search);
SearchView searchView = (SearchView) searchItem.getActionView();
searchView.setOnQueryTextListener(this);
return true;
}
//getting text from user
#Override
public boolean onQueryTextChange(String newText) {
activity.getFilter().filter(newText);
return false;
}
//submitting Text
#Override
public boolean onQueryTextSubmit(String newText) {
activity.getFilter().filter(newText);
return false;
}
This is other Activity
public Filter getFilter() {
return filter;
}
private Filter filter = new Filter() {
#Override
protected FilterResults performFiltering(CharSequence constraint) {
List<Pokemon> to_be_filtered = new ArrayList<>();
String filterPattern = constraint.toString().toLowerCase().trim();
//implement search
if(filterPattern.isEmpty()) {
to_be_filtered.addAll(fulllist);
}
else {
for (some this iterate over ) {
if (get_name_of_required
search.getName().toLowerCase().contains(filterPattern)) {
add_created_database_to_be_filtered.add(name of list variable);
}
}
}
In this you have to use inbuilt function called getfilter() it will handle Search bar.
Here I had used statements like to_be_filtered and add_created_database, You have to modify code according to database you are using.
I my case I am having 2 activities in which the first three class i.e. OnQuerySearch... , Submit text and Save text are in MainActivity and getFilter() is in another Activity
Thanks I hope you got your answer
hopefully you can help me. First of all, let me explain what my problem is.
I have two ViewModels. The first one has e.g. stored information in several textboxes.
For example
private static string _tbxCfgLogfile;
public string TbxCfgLogfile
{
get { return _tbxCfgLogfile; }
set
{
_tbxCfgLogfile = value;
NotifyOfPropertyChange(() => TbxCfgLogfile);
}
}
The other ViewModel has a Button where i want to save this data from the textboxes.
It does look like this
public bool CanBtnCfgSave
{
get
{
return (new PageConfigGeneralViewModel().TbxCfgLogfile.Length > 0 [...]);
}
}
public void BtnCfgSave()
{
new Functions.Config().SaveConfig();
}
How can i let "CanBtnCfgSave" know that the condition is met or not?
My first try was
private static string _tbxCfgLogfile;
public string TbxCfgLogfile
{
get { return _tbxCfgLogfile; }
set
{
_tbxCfgLogfile = value;
NotifyOfPropertyChange(() => TbxCfgLogfile);
NotifyOfPropertyChange(() => new ViewModels.OtherViewModel.CanBtnCfgSave);
}
}
It does not work. When i do remember right, i can get the data from each ViewModel, but i cannot set nor Notify them without any effort. Is that right? Do i have to use an "Event Aggregator" to accomplish my goal or is there an alternative easier way?
Not sure what you are doing in your viewmodels - why are you instantiating viewmodels in property accessors?
What is this line doing?
return (new PageConfigGeneralViewModel().TbxCfgLogfile.Length > 0 [...]);
I can't be sure from your setup as you haven't mentioned much about the architecture, but sincce you should have an instance of each viewmodel, there must be something conducting/managing the two (or one managing the other)
If you have one managing the other and you are implementing this via concrete references, you can just pick up the fields from the other viewmodel by accessing the properties directly, and hooking the PropertyChanged event of the child to notify the parent
class ParentViewModel : PropertyChangedBase
{
ChildViewModel childVM;
public ParentViewModel()
{
// Create child VM and hook up event...
childVM = new ChildViewModel();
childVM.PropertyChanged = ChildViewModel_PropertyChanged;
}
void ChildViewModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
// When any properties on the child VM change, update CanSave
NotifyOfPropertyChange(() => CanSave);
}
// Look at properties on the child VM
public bool CanSave { get { return childVM.SomeProperty != string.Empty; } }
public void Save() { // do stuff }
}
class ChildViewModel : PropertyChangedBase
{
private static string _someProperty;
public string SomeProperty
{
get { return _someProperty; }
set
{
_someProperty = value;
NotifyOfPropertyChange(() => SomeProperty);
}
}
}
Of course this is a very direct way to do it - you could just create a binding to CanSave on the child VM if that works, saving the need to create the CanSave property on the parent
In my windows phone app, I need to track some events to get a good flow. But I'm not sure how to handle them in good sequence.
What needs to be done at startup of the app:
Main view is loaded and corresponding view model instantiated
In the constructor of the view model I initiate a login sequence that signals when completed with an eventhandler
Now when the login sequence has finished AND the view is completely loaded I need to startup another sequence.
But here is the problem, the order of these 2 events 'completing' is not always the same...
I've use the EventToCommand from MVVMLight to signal the view model that the view has 'loaded'.
Any thoughts on how to synchronize this.
As you should not use wait handles or something similar on the UI thread. You will have to sync the two method using flags in your view model and check them before progressing.
So, implement two boolean properties in your view model. Now when the login dialog is finished set one of the properties (lets call it IsLoggedIn) to true, and when the initialization sequence is finished you set the other property (how about IsInitialized) to true. The trick now lies in the implementation of the setter of these two properties:
#region [IsInitialized]
public const string IsInitializedPropertyName = "IsInitialized";
private bool _isInitialized = false;
public bool IsInitialized {
get {
return _isInitialized;
}
set {
if (_isInitialized == value)
return;
var oldValue = _isInitialized;
_isInitialized = value;
RaisePropertyChanged(IsInitializedPropertyName);
InitializationComplete();
}
}
#endregion
#region [IsLoggedIn]
public const string IsLoggedInPropertyName = "IsLoggedIn";
private bool _isLoggedIn = false;
public bool IsLoggedIn {
get {
return _isLoggedIn;
}
set {
if (_isLoggedIn == value)
return;
var oldValue = _isLoggedIn;
_isLoggedIn = value;
RaisePropertyChanged(IsLoggedInPropertyName);
InitializationComplete();
}
}
#endregion
public void InitializationComplete() {
if (!(this.IsInitialized && this.IsLoggedIn))
return;
// put your code here
}
Alternatively you can remove the InitializationComplete from the setters and change InitializationComplete to:
public void InitializationComplete() {
// put your code here
}
Then subscribe to the 'PropertyChanged' event use the following implementation:
private void Class1_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e) {
if (e.PropertyName == IsInitializedPropertyName || e.PropertyName == IsLoggedInPropertyName) {
if (this.IsInitialized && this.IsLoggedIn)
InitializationComplete();
}
}
I want to extract the guard statement from the following method
private void CreateProxy()
{
//extract the following guard statement.
Host selected = this.comboBox1.SelectedItem as Host;
if (selected == null)
{
return;
}
this.SearchProxy = ServiceProxy.ProxyFactory.CreateSearchProxy(GetSelectedIP().ToString());
this.StreamProxy = ServiceProxy.ProxyFactory.CreatePlayerProxy(GetSelectedIP().ToString());
}
//extracted guard method
public bool IsHostSelected()
{
Host selected = this.comboBox1.SelectedItem as Host;
if (selected == null)
{
return false;
}
return true;
}
see? now i have to add return value for the extracted method, is this kinda ugly?
any better solution to avoid adding the return value for the extracted method?
I don't see the big deal. First, I would rewrite it as:
static bool SelectedItemIsHost(ComboBox box) {
return box.SelectedItem is Host;
}
Note the rename, the ComboBox as a parameter, and the body change.
Now, this makes your code read more clearly:
void CreateProxy() {
if(SelectedItemIsHost(this.comboBox1)) {
this.SearchProxy = ServiceProxy.ProxyFactory.CreateSearchProxy(GetSelectedIP().ToString());
this.StreamProxy = ServiceProxy.ProxyFactory.CreatePlayerProxy(GetSelectedIP().ToString());
}
}
So now it reads "if the selected item is a Host then do stuff."
Now, this goes way beyond your question, but this looks like a big coupling of UI logic and domain logic. You might want to reconsider a decoupling there.
any better solution to avoid adding the return value for the extracted method?
Yes:
//extracted guard method
public bool IsHostSelected()
{
Host selected = this.comboBox1.SelectedItem as Host;
return selected != null;
}