I just began to learn data binding and I have some troubles in understanding its technique
in my following code, I have enabled data binding in the app Gradle file in order to use it and get rid of the findviewbyid() ... So I've created the binding variable as lateinit before the oncreate() function and then I initialized it in the on create fun like this: binding = DataBindingUtil.setContentView(this, R.layout.activity_main) and I will give you an example of a view in my XML file to complete on ...
<EditText
android:id="#+id/nickName_editText"
style="#android:style/Widget.DeviceDefault.Light.EditText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="#dimen/Margin"
android:layout_marginTop="#dimen/Margin"
android:layout_marginRight="#dimen/Margin"
android:hint="#string/hint"
android:inputType="textPersonName"
android:textAlignment="center" />
Back to the kotlin file what is the difference between these two lines of code below (*Both lines are working)
nickName_editText.visibility = View.VISIBLE
binding.nickNameEditText.visibility = View.VISIBLE
I know that we want to get rid of the findviewbyid() to make the app faster but why don't we do it like in the first line and we are not calling findViewById() too
I'm new to android development so I might not be able to understand that complicated answers :‑D
Thanks for helping!
These are both forms of data binding, binding.nicknameEditText is Androids implementation, and the recommended approach. "nickName_editText" is Kotlin data binding and has known bug issues, when you get into more complicated views they'll start to pop up.
Expanded your imports in the MainActivity, you'll notice the following import.
import kotlinx.android.synthetic.main.activity_main.*
The start indicates binding for all views in the layout.
If you "remove kotlinx.android.synthetic.main.activity_main.*" you'll notice that the "nickName_EditText" is now undefined.
You can also view the Kotlin byte code by
clicking on tools/Kotlin/show Kotlin ByteCode
If you click on "nickName_editText" you'll notice the bytecode for this section will be highlighted.
Hopefully, this answers all your questions
I have the following XML with data binding:
<EditText
android:id="#+id/addvalue"
android:inputType="numberDecimal"
android:digits="0123456789,€"
android:text="0,00 €"/>
<Button
android:id="#+id/add"
android:onClick="#{() -> fragment.addManualPosition(addvalue.text)}"/>
I get the error
"data binding error ****msg:if getId is called on an expression, it should have an id: addvalue.text"
I can not find anything at all that would help me understand what this error is supposed to mean or how to fix it.
I found it myself.
However because there is absolutely nothing written about this error message and it being extremely misleading, I'll keep the question online.
Fix:
The lambda is a perfectly fine Kotlin lambda.
However Data Binding seems to generate Java code.
So it must not be addvalue.text but addvalue.getText() .
I have an Android Application and use Xamarin and MvvmCross. I have a EditText and would like to call a command everytime the text changes.
The command in the VM:
public MvxCommand<string> SearchContactsCommand => new MvxCommand<string>(SearchContacts);
private void SearchContacts(string searchTerm)
{
// Do search
}
And this is the Edit box:
<android.support.design.widget.TextInputLayout
android:layout_marginTop="3dp"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
local:MvxLang="Hint SearchPlaceholder"
local:MvxBind="TextChanged SearchContactsCommand" />
</android.support.design.widget.TextInputLayout>
I tried it with different variations of TextChanged without success.
If possible I would like to avoid having a property on the VM for the searchterm and execute the search in the setter of it.
Is there any way how I can achieve that or do I have to write a custom binding?
Version:
- MvvmCross 5.6.3
- MvvmCross.Binding 5.6.3
Currently there is no built in binding that can do that, you'll have to do a custom one. Here you can see almost all of the built bindings there are. The others are in Droid support plugins in the Mvx{NameOfTheDroidSupportPart}SetupHelper.cs files like MvxPreferenceSetupHelper.cs inside MvvmCross.Droid.Support.V7.Preference if you want to see them too.
I'm not sure what you are aiming with that but if you want to do an autocomplete you can use MvxAutoCompleteTextView. Here you have an example. And also look into this that is the binding the autocomplete uses to fire the change every time the value changes you just have to adapt it to trigger a command with the value as the parameter.
Any problem just ask and I'll be glad to help
I am using MvvmCross with Xamarin.Android. I have the Visibility plugin installed. In my Android application project, I have created an Android-specific visibility converter that supports the Invisible state (view not shown, but still taking up layout space):
public class VisibleOrInvisibleValueConverter
: MvxValueConverter<bool, ViewStates>
{
public ViewStates Convert(bool value, Type targetType, CultureInfo cultureInfo, object parameter)
{
MvxTrace.Error("VisibleOrInvisibleValueConverter.Convert");
return value ? ViewStates.Visible : ViewStates.Invisible;
}
}
In my .axml markup, I use this converter like this:
<FrameLayout
android:layout_width="0dip"
android:layout_height="5dip"
android:layout_weight="1"
android:background="#ff0000"
local:MvxBind="Visibility Selected, Converter=VisibleOrInvisible, FallbackValue=0" />
Based on the documentation at https://github.com/MvvmCross/MvvmCross/wiki/Value-Converters#referencing-value-converters-in-touch-and-droid, I believe that MvvmCross will automatically discover the existence of this value converter, since it is in my UI project.
At runtime, the bound value always takes on the fallback value, no matter what the value of Selected is. Based on the documentation at https://github.com/MvvmCross/MvvmCross/wiki/Value-Converters#referencing-value-converters-in-touch-and-droid, this means that either my binding source path is missing, or the value converter threw an exception.
Unfortunately, I think I can rule both of those out. For the first possibility, I tried replacing my custom VisibleOrInvisible converter with the stock MvvmCross Visibility converter, and it worked fine. (That is, the binding worked fine. The stock Visibility converter doesn't support my desired behavior, though.) Anyway, I think this shows that the source path (Selected) does exist.
For the second possibility, I've set a breakpoint in the Convert function of the VisibleOrInvisible converter, and it is never executed. I also added an MvxTrace call in there, and I never see the trace message.
Although my converter is supposed to be automatically discovered, I have also tried explicitly adding my platform-specific assembly to the list of assemblies that implement value converters by overriding the ValueConverterAssemblies property getter in Setup.cs:
protected override List<Assembly> ValueConverterAssemblies
{
get
{
var toReturn = base.ValueConverterAssemblies;
toReturn.Add(typeof (VisibleOrInvisibleValueConverter).Assembly);
return toReturn;
}
}
But this did not help.
I think that MvvmCross is discovering my converter OK. If I intentionally refer to a non-existent converter in my .axml file, I see exception messages in the debug trace at runtime. But when I specify my VisibleOrInvisible converter, these messages do not appear.
My working theory is that an exception is occurring in the process of invoking my converter, before the only line of code in the converter is executed. But I don't know how to get to the bottom of that. No exception messages appear in the debug trace.
Is there a simple step that I'm getting wrong? I've studied the MvvmCross ValueConversion example pretty carefully, and I think I'm doing everything that example does.
I've just taken the ValueConversion sample, upgraded the core csproj file to profile 158 and then inserted your value converter.
This converter was picked up fine - I could see it in the converter list using:
protected override void InitializeLastChance ()
{
base.InitializeLastChance ();
var registry = Mvx.Resolve<IMvxValueConverterLookup> ();
var f = registry.Find("VisibleOrInvisible");
Mvx.Trace ("Custom converter was found : {0}", f != null);
}
However, when I tried to use it I saw binding errors about enum/bool/value type mapping... so I can see there is some problem...
After a little digging, it seems the reason for this problem was because your ValueConverter implements an unusual public ViewStates Convert method, instead of overriding the base class Convert method. To fix this I changed the converter to:
public class VisibleOrInvisibleValueConverter
: MvxValueConverter<bool, ViewStates>
{
protected override ViewStates Convert (bool value, Type targetType, object parameter, CultureInfo culture)
{
MvxTrace.Error("VisibleOrInvisibleValueConverter.Convert");
return value ? ViewStates.Visible : ViewStates.Invisible;
}
}
For more on authoring value converters using the MvxValueConverter<...> helpers, see https://github.com/MvvmCross/MvvmCross/wiki/Value-Converters#using-the-mvxvalueconverter-helper (if there's some other sample or document somewhere that has the wrong sample, then "sorry" and please point it out to whoever owns it so they can fix it)
Further, you may find the source for MvxValueConverter helpful - it's hopefully pretty straight-forward to follow how it implements IMvxValueConverter: https://github.com/MvvmCross/MvvmCross/blob/v3.1/CrossCore/Cirrious.CrossCore/Converters/MvxValueConverter.cs
With that problem solved, the next challenge presented by this question is how to use the FallbackValue. I've not fully analysed the trace I saw from this problem but I did experiment with a few other FallbackValue syntax examples - and these all seemed to work correctly:
<FrameLayout
android:layout_width="fill_parent"
android:layout_height="200dp"
android:background="#ff0000"
local:MvxBind="Visibility VisibleOrInvisible(ThisWillNotBeFound), FallbackValue=Visible" />
<FrameLayout
android:layout_width="fill_parent"
android:layout_height="200dp"
android:background="#ff0000"
local:MvxBind="Visibility VisibleOrInvisible(ThisWillNotBeFound), FallbackValue=Invisible" />
<FrameLayout
android:layout_width="fill_parent"
android:layout_height="200dp"
android:background="#ffff00"
local:MvxBind="Visibility VisibleOrInvisible(ThisWillNotBeFound, FallbackValue=true)" />
<FrameLayout
android:layout_width="fill_parent"
android:layout_height="200dp"
android:background="#0000ff"
local:MvxBind="Visibility VisibleOrInvisible(ThisWillNotBeFound, FallbackValue=false)" />
I'm not sure if the numeric fallback value is working for this case currently - suspect it needs more investigation (will log as a potential issue).
I have a list view which binds to an array of strings as such:
<Mvx.MvxListView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
local:MvxBind="ItemsSource StringArray"
local:MvxItemTemplate="#layout/listitem_view" />
My item template is simply just a text view...
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
which bound fine using JSON...
local:MvxBind="{'Text':{'Text':''}}" />
and again using Swiss...
local:MvxBind="Text " />
but after updating Mvx to 3.10 I'm now not getting anything bound to my text view even though the list is still bound to the list view. Has the syntax in Rio binding changed the default behaviour?
There was no intended change to this area in 3.0.10 - although there was a fix for this Error when making bind ObservableCollection<string> for a MvxListView - fix was https://github.com/slodge/MvvmCross/commit/d325fb75eaeeb8e470e0ac551f2b69b441f7b285. I believe this was released and worked in 3.0.10 for a test app.
Has the syntax in Rio binding changed the default behaviour?
I don't know if anyone has seen any issues with these in MethodBinding or FieldBinding as part of the Rio extensions. I've not heard of any.
If this is broken - and depending on whether this is broken due to the binding engine (Tibet) or the Method and Field extensions (Rio) or something else, then possible workarounds include:
switching away from Rio
using the period "." alternative to empty space - e.g. local:MvxBind="Text ."
adding a public object HackSelf { get { return this; } property to the bound object and binding to that local:MvxBind="Text HackSelf"
overriding the registered binding engine (e.g. back to Swiss)
If this is broken - it might also be a good idea to log an issue on github for this - including modules loaded, use case, version used, any suspicious trace output seen and a link back here.