Android自定义视图状态保存：避免直接序列化Drawable对象的策略

public class MyCustomView extends View {
    private Drawable picture;
    private Float degree = 0f;

    // ... 构造函数和绘制逻辑 ...

    private static class SavedState extends BaseSavedState {
        // 错误：直接存储Drawable对象
        Drawable picture; 
        Float degree = 0f;

        public SavedState(Parcelable superState) {
            super(superState);
        }

        public SavedState(Parcel source) {
            super(source);
            degree = source.readFloat();
            // 错误：尝试将非Parcelable的Drawable读出
            // 这会导致 ClassCastException
            picture = source.readParcelable(getClass().getClassLoader()); 
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeFloat(degree);
            // 错误：尝试将非Parcelable的Drawable写入
            out.writeParcelable((Parcelable) picture, flags); // 这里会抛出 ClassCastException
        }

        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

    @Nullable
    @Override
    protected Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState myState = new SavedState(superState);
        myState.degree = this.degree;
        myState.picture = this.picture; // 将Drawable对象赋值给SavedState
        return myState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }
        SavedState savedState = (SavedState) state;
        super.onRestoreInstanceState(savedState.getSuperState());
        this.degree = savedState.degree;
        this.picture = savedState.picture; // 恢复Drawable对象
        invalidate();
    }
}

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.view.View;

import androidx.annotation.Nullable;
import androidx.annotation.RequiresApi; // 如果使用API 21+的getDrawable方法

public class MyCustomView extends View {

    private Drawable picture;
    private int pictureResId; // 用于保存Drawable的资源ID
    private Float degree = 0f;

    public MyCustomView(Context context) {
        super(context);
        init();
    }

    public MyCustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public MyCustomView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        // 示例：初始化一个Drawable，并记录其资源ID
        // 假设您的Drawable是从R.drawable.my_vector_image加载的
        // 在实际应用中，您可能通过属性设置或在代码中动态设置
        this.pictureResId = R.drawable.my_vector_image; // 假设您的资源ID
        this.picture = getContext().getDrawable(pictureResId);
        // ... 其他初始化逻辑
    }

    // 设置Drawable的方法，同时更新资源ID
    public void setPicture(int resId) {
        this.pictureResId = resId;
        this.picture = getContext().getDrawable(resId);
        invalidate();
    }

    // ... 绘制逻辑 (使用this.picture进行绘制) ...

    private static class SavedState extends BaseSavedState {
        int drawableResId; // 保存Drawable的资源ID
        Float degree = 0f;

        public SavedState(Parcelable superState) {
            super(superState);
        }

        public SavedState(Parcel source) {
            super(source);
            degree = source.readFloat();
            drawableResId = source.readInt(); // 读取资源ID
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeFloat(degree);
            out.writeInt(drawableResId); // 写入资源ID
        }

        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

    @Nullable
    @Override
    protected Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState myState = new SavedState(superState);
        myState.degree = this.degree;
        myState.drawableResId = this.pictureResId; // 保存Drawable的资源ID
        return myState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }
        SavedState savedState = (SavedState) state;
        super.onRestoreInstanceState(savedState.getSuperState());
        this.degree = savedState.degree;

        // 恢复Drawable对象：根据资源ID重新加载
        if (savedState.drawableResId != 0) { // 确保资源ID有效
            this.pictureResId = savedState.drawableResId;
            // 推荐使用带Theme的getDrawable方法，尤其是在API 21+
            if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
                this.picture = getContext().getDrawable(this.pictureResId, getContext().getTheme());
            } else {
                this.picture = getContext().getResources().getDrawable(this.pictureResId);
            }
        }
        invalidate(); // 重新绘制视图
    }
}