双向数据绑定不更新UI [英] Two-Way Databinding not updating UI

问题描述

我试图理解为什么设置值不会自动刷新UI.如果我调用binding.setItem，则UI会刷新.

I am trying to understand why setting a value does not automatically refresh the UI. If I call binding.setItem, the UI refreshes.

我知道绑定对象包含更新后的值，但是在设置item.name和item.checked之后不会刷新UI.

I know binding object contains the updated values, but the UI is not being refreshed after setting item.name and item.checked.

我做错了什么?我是否需要每次都调用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.

What am I doing wrong? Do I need to call setItem everytime to refresh the UI? I would think that this would be unnecessary, since the UI would automatically update after setting a value.

Item.java:

Item.java:

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

MainActivity.java:

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:

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>

build.gradle:

build.gradle:

android {
...
    dataBinding{
        enabled=true
    }

}

推荐答案

根据开发人员指南:

任何普通的旧Java对象(PO​​JO)都可以用于数据绑定，但是修改POJO不会导致UI更新.

Any plain old Java object (POJO) may be used for data binding, but modifying a POJO will not cause the UI to update.

您可以按照开发者指南的可观察对象"部分进行操作，以允许修改您的对象以更新UI.

You can follow the developer guide's "Observable Objects" section to allow modification of your object to update your UI.

https://developer.android.com/topic/libraries/data-binding/index.html#data_objects

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