Android 双向数据绑定不更新UI

我试图理解为什么设置值不会自动刷新UI。如果调用binding.setItem，UI将刷新

我知道binding对象包含更新的值，但在设置item.name和item.checked后，UI不会刷新

我做错了什么？我是否需要每次调用setItem来刷新UI？我认为这是不必要的，因为UI会在设置值后自动更新

Item.java：

public class Item  {
    public String name;
    public Boolean checked;
}

MainActivity.java：

public class MainActivity extends AppCompatActivity {

    public Item item;
    ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        item = new Item();
        item.checked = true;
        item.name = "a";

        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        binding.setItem(item);
    }

    public void button_onClick(View v) {
        item.checked = !item.checked;
        item.name = item.name  + "a";
        ///binding.setItem(item); --> ??? this updates UI, do I need to call this to refresh UI everytime???
    }
}

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <variable
            name="item"
            type="com.example.abc.twowaydatabinding.Item" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:id="@+id/tv_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@={item.name}"
            android:textSize="20sp" />


        <Switch
            android:id="@+id/switch_test"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:checked="@={item.checked}" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="change"
            android:onClick="button_onClick"/>

    </LinearLayout>
</layout>

---

根据开发者指南：

任何普通的旧Java对象（POJO）都可以用于数据绑定，但修改POJO不会导致UI更新

您可以按照《开发人员指南》的“可观察对象”部分来修改对象以更新UI

---

如前所述，使用可观察字段

public ObservableField<Boolean> checked = new ObservableField<>();

public ObservableField<String> name = new ObservableField<>();

---

顺便说一句，您可以查看关于数据绑定的博客文章系列，为了更新UI，需要观察字段。只需更新我的更改：

import android.databinding.BaseObservable;
import android.databinding.Bindable;

public class Item extends BaseObservable {
    private String name;
    private Boolean checked;
    @Bindable
    public String getName() {
        return this.name;
    }
    @Bindable
    public Boolean getChecked() {
        return this.checked;
    }
    public void setName(String name) {
        this.name = name;
        notifyPropertyChanged(BR.name);
    }
    public void setChecked(Boolean checked) {
        this.checked = checked;
        notifyPropertyChanged(BR.checked);
    }
}

    item = new Item();
    item.checked.set(true);
    item.name.set("a");

    binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
    binding.setItem(item);
}

public void button_onClick(View v) {

    item.checked.set(!(item.checked.get()));
    item.name.set(item.name.get()  + "a");

}

import android.databinding.BaseObservable;
import android.databinding.Bindable;

public class Item extends BaseObservable {
    private String name;
    private Boolean checked;
    @Bindable
    public String getName() {
        return this.name;
    }
    @Bindable
    public Boolean getChecked() {
        return this.checked;
    }
    public void setName(String name) {
        this.name = name;
        notifyPropertyChanged(BR.name);
    }
    public void setChecked(Boolean checked) {
        this.checked = checked;
        notifyPropertyChanged(BR.checked);
    }
}