Question

方法onSaveInstanceState()和onRestoreInstanceState(Parcelable state)在View类中声明受保护，而在某些子类中，如TextView或ListView，它们是公开宣布。要在配置更改后保存并恢复ListView的状态，我可以直接使用这些方法，而我不能用View之类的其他ScrollView。为什么这些方法在View类中没有公开？我应该直接从我的Activity / Fragment或其他方式调用这些方法吗？要恢复ScrollView的状态，我可以使用自定义子类将这些方法的可见性更改为public：这是要走的路吗？

import android.content.Context;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.widget.ScrollView;

public class MyScrollView extends ScrollView {

    public MyScrollView(Context context) {
        super(context);
    }

    public MyScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MyScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        super.onRestoreInstanceState(state);
    }

    @Override
    public Parcelable onSaveInstanceState() {
        return super.onSaveInstanceState();
    }

}

Answer 1

- Why those methods are not declared public in the View class?

这是因为它们仅用于包含View，请记住ScrollView是ViewGroup的子类，主要用于存储其他视图。

来自documentation：

A ViewGroup is a special view that can contain other views (called children.) 
The view group is the base class for layouts and views containers

- To restore the state of a ScrollView I can use a custom subclass that change the visibility of those methods to public

是的，你可以，但它只是一个容器，没有什么特别的保存，你也可以发布它只会重新计算它的位置

来自documentation：

 For example, you will never store your current position on screen because that will be 
 computed again when a new instance of the view is placed in its view hierarchy.

Some examples of things you may store here: the current cursor position in a text view 
(but usually not the text itself since that is stored in a content provider or other 
persistent storage), the currently selected item in a list view.

onSaveInstanceState和onRestoreInstanceState的可见性

1 个答案: