Android自定义视图：如何正确保存包含Drawable的状态

// 错误的SavedState实现示例
private static class SavedState extends BaseSavedState {
    Drawable picture; // 问题所在：Drawable不是Parcelable
    Float degree = 0f;

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

    public SavedState(Parcel source) {
        super(source);
        degree = source.readFloat();
        // 尝试读取Drawable，会抛出ClassCastException
        picture = source.readParcelable(getClass().getClassLoader());
    }

    @Override
    public void writeToParcel(Parcel out, int flags) {
        super.writeToParcel(out, flags);
        out.writeFloat(degree);
        // 尝试写入Drawable，如果picture不是Parcelable，会抛出ClassCastException
        out.writeParcelable((Parcelable) picture, flags);
    }

    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];
        }
    };
}

// 错误的转换尝试
protected Parcelable onSaveInstanceState() {
    // ... 其他代码
    Bitmap bitmap = ((BitmapDrawable) picture).getBitmap(); // 问题：VectorDrawable不能直接转换为BitmapDrawable
    out.writeParcelable(bitmap, flags);
    // ... 其他代码
}

import android.content.Context;
import android.graphics.Canvas;
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.core.content.ContextCompat; // 推荐使用ContextCompat兼容旧版本API

public class MyCustomView extends View {

    private Drawable picture;
    private float degree = 0f;
    private int drawableResId = 0; // 保存Drawable的资源ID

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

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

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

    private void init(@Nullable AttributeSet attrs) {
        // 假设这里初始化了picture，例如从XML属性或默认资源加载
        // 为了演示，我们手动设置一个默认的Drawable
        // 注意：在实际应用中，你需要确保drawableResId在Drawable被设置时同步更新
        setPictureFromResource(R.drawable.ic_launcher_foreground); // 假设这是一个VectorDrawable
        // 其他初始化逻辑...
    }

    // 设置Drawable的方法，同时保存其资源ID
    public void setPictureFromResource(int resId) {
        this.drawableResId = resId;
        this.picture = ContextCompat.getDrawable(getContext(), resId);
        if (this.picture != null) {
            this.picture.setBounds(0, 0, getWidth(), getHeight()); // 设置边界，根据实际需求调整
        }
        invalidate(); // 刷新视图
    }

    // 设置Drawable的方法，如果不是来自资源，则drawableResId可以设置为0
    public void setPicture(Drawable drawable) {
        this.picture = drawable;
        this.drawableResId = 0; // 非资源Drawable不保存ID
        if (this.picture != null) {
            this.picture.setBounds(0, 0, getWidth(), getHeight());
        }
        invalidate();
    }

    public void setDegree(float degree) {
        this.degree = degree;
        invalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.save();
        canvas.rotate(degree, getWidth() / 2f, getHeight() / 2f);
        if (picture != null) {
            picture.draw(canvas);
        }
        canvas.restore();
    }

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

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        // 检查状态类型，避免ClassCastException
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }
        SavedState savedState = (SavedState) state;
        super.onRestoreInstanceState(savedState.getSuperState());
        this.degree = savedState.degree;
        this.drawableResId = savedState.drawableResId;

        // 根据保存的资源ID重新创建Drawable
        if (this.drawableResId != 0) {
            this.picture = ContextCompat.getDrawable(getContext(), this.drawableResId);
            if (this.picture != null) {
                this.picture.setBounds(0, 0, getWidth(), getHeight()); // 重新设置边界
            }
        } else {
            this.picture = null; // 如果没有ID，则清除Drawable
        }
        invalidate(); // 刷新视图以显示恢复后的状态
    }

    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];
            }
        };
    }
}