how to serialize an object of android.graphics.Pat

问题:

I'm trying to store objects of Android.graphics.Path in internal device memory. Does anyone know how to serialize a android.graphics.Path object? And also, is there any other way of storing a Path object? Thanks.

回答1:

The way I did it is to identify the methods that I needed from the original Path class and then simply override those methods as follows:

public class CustomPath extends Path implements Serializable {

private static final long serialVersionUID = -5974912367682897467L;

private ArrayList<PathAction> actions = new ArrayList<CustomPath.PathAction>();

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException{
    in.defaultReadObject();
    drawThisPath();
}

@Override
public void moveTo(float x, float y) {
    actions.add(new ActionMove(x, y));
    super.moveTo(x, y);
}

@Override
public void lineTo(float x, float y){
    actions.add(new ActionLine(x, y));
    super.lineTo(x, y);
}

private void drawThisPath(){
    for(PathAction p : actions){
        if(p.getType().equals(PathActionType.MOVE_TO)){
            super.moveTo(p.getX(), p.getY());
        } else if(p.getType().equals(PathActionType.LINE_TO)){
            super.lineTo(p.getX(), p.getY());
        }
    }
}

public interface PathAction {
    public enum PathActionType {LINE_TO,MOVE_TO};
    public PathActionType getType();
    public float getX();
    public float getY();
}

public class ActionMove implements PathAction, Serializable{
    private static final long serialVersionUID = -7198142191254133295L;

    private float x,y;

    public ActionMove(float x, float y){
        this.x = x;
        this.y = y;
    }

    @Override
    public PathActionType getType() {
        return PathActionType.MOVE_TO;
    }

    @Override
    public float getX() {
        return x;
    }

    @Override
    public float getY() {
        return y;
    }

}

public class ActionLine implements PathAction, Serializable{
    private static final long serialVersionUID = 8307137961494172589L;

    private float x,y;

    public ActionLine(float x, float y){
        this.x = x;
        this.y = y;
    }

    @Override
    public PathActionType getType() {
        return PathActionType.LINE_TO;
    }

    @Override
    public float getX() {
        return x;
    }

    @Override
    public float getY() {
        return y;
    }

}
}

In my example I need "moveTo" and "lineTo", so in this case I simply hold the drawing information in a list. This list contains the drawing information (what I call "action") needed by Path in order to restore the drawing as it looked like before the object was serialized. Then when I deserialize my objects of type CustomPath i make sure to let the default serialization protocol call "drawThisPath", so the path is redrawn.

回答2:

I've just managed to solve this. My application is based off the FingerPaintDemo, so makes use of just moveTo and quadTo, but I think you can apply this approach to any Path functions.

First, extend Path as follows:

import android.graphics.Path;

import java.util.ArrayList;

import java.io.Serializable;

public class SerializablePath extends Path implements Serializable {

    private ArrayList<float[]> pathPoints;

    public SerializablePath() {
        super();
        pathPoints = new ArrayList<float[]>();
    }

    public SerializablePath(SerializablePath p) {
        super(p);
        pathPoints = p.pathPoints;
    }

    public void addPathPoints(float[] points) {
        this.pathPoints.add(points);
    }

    public void loadPathPointsAsQuadTo() {
        float[] initPoints = pathPoints.remove(0);
        this.moveTo(initPoints[0], initPoints[1]);
        for (float[] pointSet : pathPoints) {
            this.quadTo(pointSet[0], pointSet[1], pointSet[2], pointSet[3]);
        } 
    }
}

I don't think I need to paste the implementation code, but if you want to see it let me know. Basically just as you call something like myPath.quadTo(x1, y1, x2, y2), also call myPath.addPathPoints(new float[]{x1, y1, x2, y2}).

Serialize the object to disk as normal, and when you read it back in, just be sure to call myPath.loadPathPointsAsQuadTo().

回答3:

There is nothing so special for Path Class. Use can serialize any class that implements the Serializable interface..

Serializable interface is a Marker interface. i.e it dont have any method to implement. It just signify that the object can be deflatted to files/Memroies and later can be inflatted to be a live object again

What you do just make a class that extends your android.graphics.Path class and implements the Serializable interface. Then use this class instead of your android.graphics.Path. Then you will be able to apply serialization over it.

And check the following link for a detailed information

http://java.sun.com/developer/technicalArticles/Programming/serialization/

Hope this helps :)