如何在Android中使用DataBinding在XML视图中获取选定的值

Question

<TextView
        android:id="@+id/tv_login_or_register"
        android:layout_width="305dp"
        android:layout_height="45dp"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="28dp"
        android:background="@drawable/login_tv_bg"
        android:onClick="@{()->presenter.login(tabLoginPassword.selected)}"
        android:gravity="center"
        android:text="login"
        android:textColor="#000000"
        android:textSize="16sp" />

tabLoginPassword is a view extends TextView. The expression ()->presenter.login(tabLoginPassword.selected) turns out to be wrong,so i want to know how to get the same value as view.isSelected(),thanks!

Answer 1

The attribute android:selected doesn't support two-way binding because there is no event listener in View that notifies when that value changes. If the android:selected property were already data bound, then you wouldn't have to do anything because your expression would pick up the value from the bound expression. That is, if you used an expression like this:

<EditText android:id="@+id/tabLoginPassword"
          android:selected="@{model.passwordSelected}" .../>

Then your chained binding expression would work and be the equivalent of this:

<TextView
    android:id="@+id/tv_login_or_register"
    android:onClick="@{()->presenter.login(model.passwordSelected)}"
    .../>

I don't know how your isSelected() changes, so I expect that you have code other than data binding that sets it -- perhaps accessibility or internal code. To handle two-way data binding, you should add an event listener for the android:selected attribute and notify when the value changes.

You should use this medium article as a guide .

Here's a shortened version, but you can tailor it how you like. Definitely look at the article.

Add an event listener for when the selected value changes:

public interface OnSelectedChangedListener {
    void selectedChanged();
}

Extend your View class to support the listener:

public class TabLoginPassword extends EditText {
    private OnSelectedChangedListener mOnSelectedChangedListener;

    public void setOnSelectedChangedListener(OnSelectedChangedListener listener) {
      mOnSelectedChangedListener = listener;
    }

    @Override
    protected void dispatchSetSelected(boolean selected) {
        super.dispatchSetSelected(selected);
        if (mOnSelectedChangedListener != null) {
            mOnSelectedChangedListener.selectedChanged();
        }
    }

    //...
}

Add an BindingAdapter for the event listener:

@BindingAdapter("android:selectedAttrChanged")
public static void setSelectedChanged(TabLoginPassword view,
          final InverseBindingListener inverseBindingListener) {
    OnSelectedChangedListener listener = null;
    if (inverseBindingListener != null) {
        listener = new OnSelectedChangedListener() {
            @Override
            public void selectedChanged() {
                inverseBindingListener.onChange();
            }
        }
    }
    view.setOnSelectedChangedListener(listener);
}

Because dispatchSetSelected() isn't called unless there is a change in the selected value, you don't need to worry about infinite loops and don't have to create a BindingAdapter for the value.