如何在自定义 Preference 类上从自定义属性设置视图属性？

Question

我创建了一个类CustomPreference，它继承自androidx Preference 类，用于设置由我自己的组件组成的自定义布局。我在该自定义 Preference 类上定义了一个可样式化的属性。但现在我试图了解如何将自定义样式属性中的值传递给我的底层SpecialCustomComponent 上的属性。

CustomPreference.java

public class CustomPreference extends Preference {

  private Context context;
  private AttributeSet attrs;

  public CustomPreference(Context context, AttributeSet attrs,
      int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    this.context = context;
    this.attrs = attrs;
    setLayoutResource(R.layout.preference_widget_custom);
  }

  // other required constructor overloads omitted

  @Override
  public void onBindViewHolder(PreferenceViewHolder holder) {
    super.onBindViewHolder(holder);
    
    // calling this method here results in an error because
    // a.getResourceId(R.styleable.PreferenceWidgetCustom_preferenceTitle, 0) 
    // returns no resource Id at this point
    setPreferenceTitle(holder);
  }

  @Override
  protected void onAttachedToHierarchy(PreferenceManager preferenceManager) {
    super.onAttachedToHierarchy(preferenceManager);
    this.preferenceManager = preferenceManager;

    // alternatively, calling this method here would result in a 
    // different error, since I don't have access to the viewHolder
    // here. To make this work, I tried preserving "viewHolder" in a 
    // field inside onBindViewHolder (which I don't think I'm 
    // supposed to do anyways), but the viewHolder reference was 
    // null, so it didn't work.
    setPreferenceTitle();
  }

  // This is my incorrect attempt at setting "myText" to the value of "preferenceTitle"
  private void setPreferenceTitle(PreferenceViewHolder holder) {
    TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.PreferenceWidgetSwitchCustom, 0, 0);

    try {
      int preferenceTitleId = a
          .getResourceId(R.styleable.PreferenceWidgetCustom_preferenceTitle, 0);

      ((SpecialCustomComponent) holder.itemView).setText(a.getResources().getString(preferenceTitleId));
    }
    finally {
      a.recycle();
    }
  }
}

我在 attrs.xml 中为我的 CustomPreference 声明了一个自定义属性，我希望使用该属性在布局中设置我的自定义组件的底层“myText”属性。

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <declare-styleable name="PreferenceWidgetCustom">
    <attr name="preferenceTitle" format="string" />
  </declare-styleable>
</resources>

每个CustomPreference 的布局在preference_widget_custom.xml 中定义。注意属性“myText”，我想将其设置为上面定义的“preferenceTitle”的值。

preference_widget_custom.xml

<?xml version="1.0" encoding="utf-8"?>
<SpecialCustomComponent
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:myText="this is the field I would like to be set by 'preferenceTitle'" />

我在 PreferenceScreen 布局中使用这些首选项，如下所示：

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:title="Settings">
    <CustomPreference
        android:key="pref_one"
        app:preferenceTitle="Preference #1"/>
    <CustomPreference
        android:key="pref_two"
        app:preferenceTitle="Preference #2"/>
</PreferenceScreen>

Answer 1

将string 资源作为styleable 提供通常是错误的，这就是为什么您将简单的本地化工作过度复杂化的原因。可以使用此模式访问任何资源：[<package_name>.]R.<resource_type>.<resource_name>。

所以这将是res/values/strings.xml:

<resources>
    <string name="title_preference_01">Title 01</string>
    <string name="summary_preference_01">Summary 01</string>
    <string name="title_preference_02">Title 02</string>
    <string name="summary_preference_02">Summary 02</string>
<resources>

然后可以通过应用程序访问：

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

    <CustomPreference
        android:title="@string/title_preference_01"
        android:summary="@string/summary_preference_01"
        android:key="pref_one" />

    <CustomPreference
        android:title="@string/title_preference_02"
        android:summary="@string/summary_preference_02"
        android:key="pref_two" />

</PreferenceScreen>

Localize your app 详细解释了这一切。

---

此外，即使它是实际可样式化的值而不是通常用于本地化的字符串，您仍然需要将 PreferenceWidgetCustom 样式应用于 SpecialCustomComponent 才能访问它的值。

Answer 2

我解决了我的问题。正如 Martin 指出的那样，styleable 无论如何都不是真正用于字符串的。事实证明，使用内置的 android:title 属性而不是自定义样式让事情变得非常简单。我所要做的就是调用this.getTitle() 从我的CustomPreference 类中访问它的值。

public class CustomPreference extends Preference {

  public CustomPreference(Context context, AttributeSet attrs,
      int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    setLayoutResource(R.layout.preference_widget_custom);
  }

  // other required constructor overloads omitted

  @Override
  public void onBindViewHolder(PreferenceViewHolder holder) {
    super.onBindViewHolder(holder);
    setPreferenceTitle();
  }

  private void setPreferenceTitle() {
      ((SpecialCustomComponent) holder.itemView).setText(this.getTitle());
  }
}