Android two-way databinding, textview not updating

问题

I am trying to use MVVM pattern with android databinding. I have an edittext and a textview that should show the same text when I type in the edittext field by binding to the model via the observablefield with a LocationType model object.

From testing both fields are set to "hello" when I start the app, as expected. But when I type in the edittextfield the textview does not update, even tough the model object gets updated correctly as can be seen with by debug.

When I use an:

observablefield<String>

drop using the model and just set to some text and update the xml to use this field. It works as intended.

model:

public class LocationType {
private String locationType;

public String getLocationType() {
   return locationType;
}

public void setLocationType(String locationType) {
  this.locationType = locationType;

 }
}

modelView:

public class LocationTypeViewModel extends BaseObservable {
  @Bindable
  private    ObservableField<LocationType> locationTypeObservableField = new ObservableField<>();
  private Context context;
  LocationType locationType;

  public LocationTypeViewModel(Context context) {
    this.context = context;

    locationType = new LocationType();
    locationType.setLocationType("Hello");
    locationTypeObservableField.set(locationType);


  }

  public ObservableField<LocationType> getLocationTypeObservableField() {
    Log.d("CALLED GET", locationType.getLocationType());
    return locationTypeObservableField;
  }


}    

XML:

<layout xmlns:app="http://schemas.android.com/apk/res-auto">

<data>

    <import type="android.view.View"/>

    <variable
        name="viewModel"
        type="fragment.LocationType.viewmodel.LocationTypeViewModel"/>
</data>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical">


    <EditText
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="@{viewModel.locationTypeObservableField.locationType}"
        android:id="@+id/edittext1"/>

    <TextView
        android:layout_below="@+id/edittext1"
        android:layout_width="wrap_content"
        android:layout_height="50dp"
        android:text="@{viewModel.locationTypeObservableField.locationType}"
        android:id="@+id/text"
        />




</RelativeLayout>
</layout>

回答1:

android:text="@={viewModel.locationTypeObservableField.locationType}"

You forgot to add "=" .check and compare above line with your code.

回答2:

Two way databinding should be like this android:text="@={ProfileViewModel.mobileNumber}" You forgot to add "="

回答3:

The problem is you are observing changes to the field inside LocationTypeViewModel which points to a LocationType object. That will only notify changes when the object reference changes. What you want is an observer on the actual String field.

You are also missing an important two-binding symbol on your EditText. You want to use @={obj.fieldName} instead of @{obj.fieldName}. The @= signals that you want changes to propagate back to the source.

Here is your code edited to work as intended:

public class LocationType {

    private String location;

    public LocationType(String location) {
        this.location = location;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }
}

public class LocationTypeViewModel extends BaseObservable {

    private final LocationType locationType;

    public LocationTypeViewModel() {
        locationType = new LocationType("Hello");
    }

    @Bindable
    public String getLocation() {
        return locationType.getLocation();
    }

    public void setLocation(String location) {
        locationType.setLocation(location);
        notifyPropertyChanged(BR.location);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>

        <import type="android.view.View"/>

        <variable
            name="viewModel"
            type=".LocationTypeViewModel"/>
    </data>

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:orientation="vertical">


        <EditText
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:text="@={viewModel.location}"
            android:id="@+id/edittext1"/>

        <TextView
            android:layout_below="@+id/edittext1"
            android:layout_width="wrap_content"
            android:layout_height="50dp"
            android:text="@{viewModel.location}"
            android:id="@+id/text"
            />

    </RelativeLayout>
</layout>

来源：https://stackoverflow.com/questions/45640618/android-two-way-databinding-textview-not-updating