Question

我的应用程序工作正常但是当屏幕方向改变时，表面视图会被清除。我正在使用路径绘制自由的手。我正在尝试使用路径的arraylist将其恢复到原始状态。

下面是我初始化arraylist

的类的构造函数

public DrawThread(Context context){

            this.context = context;
            paths = new ArrayList<Path>();  //this is the arraylist in which i store path.
            //path = new Path();
            paint = new Paint();
            paint.setColor(Color.RED);
            paint.setStrokeWidth(5);
            paint.setAntiAlias(true);
            paint.setStyle(Paint.Style.STROKE);
        }

以下是负责绘制路径的函数

boolean doTouchEvent(MotionEvent event) {   

            int eventaction = event.getAction();
            int X = (int)event.getX();
            int Y = (int)event.getY();
            switch (eventaction ) {
            case MotionEvent.ACTION_DOWN:

                path = new Path();



                path.moveTo(X, Y);
                path.lineTo(X, Y);

                 break;
            case MotionEvent.ACTION_MOVE:
                //path.close();
                //path.moveTo(lastX, lastY);
                path.lineTo(X, Y);


             break;
            case MotionEvent.ACTION_UP:
                path.lineTo(X, Y);

                //path.setLastPoint(X, Y);
                paths.add(path);


            break;
            }
            drawOnCanvas();

            return true;
    }


private void drawOnCanvas(){

            Canvas canvas = null;
            try{
                canvas = sHolder.lockCanvas(null);

                    if(canvas != null & path!= null){

                            canvas.drawPath(path, paint);

                }
            }finally {
                if(canvas!=null){
                    sHolder.unlockCanvasAndPost(canvas);
                }
            }

        }

下面是负责将surfaceview恢复到原始状态的函数。

当屏幕方向改变时调用setSurfaceSize。

public void setSurfaceSize(int width , int height){

            sWidth = width;
            sHeight = height;
            redrawall();

        }
private void redrawall(){
            Canvas canvas = null;
            int i = 0;
            try{
                canvas = sHolder.lockCanvas(null);

                    if(canvas != null & paths!= null){
                        if(paths.isEmpty()){
                            Toast.makeText(context, "empty", Toast.LENGTH_SHORT).show();
                        }
                        for (Path pp : paths){    
                            canvas.drawPath(pp, paint);
                        }

                        }

            }finally {
                if(canvas!=null){
                    sHolder.unlockCanvasAndPost(canvas);
                }
            }
        }

问题是路径（arraylist）始终为空，旋转后屏幕保持空白。

Answer 1

对于设备的每次旋转，Activity都会被销毁并重新创建。它会调用onPause()，onStop()，并回忆onCreate()，onStart()，onResume()，以便自定义视图。因此，DrawThread被停止并销毁并重新调用其初始化方法（其构造函数）。然后，每次使用此行创建一个新的ArrayList：

// this list is obviously empty at its creation ;)
paths = new ArrayList<Path>();

为了防止这种情况，请在轮换之前使用Parcelable对象存储列表的状态，然后将其恢复。您可能需要创建一个自定义Path对象来实现Parcelable对象，然后保存ArrayList。通过对互联网的一点研究，您可以在视图中找到这些方法：

// Saves current instance of class
@Override
public Parcelable onSaveInstanceState() { ... }

// Restores current instance of class
@Override
public void onRestoreInstanceState(Parcelable state) { ... }

// State of class
private static class SavedState extends BaseSavedState {
    ...
    @Override
    public void writeToParcel(Parcel out, int flags) { ... }

    public static final Parcelable.Creator<SavedState> CREATOR =
            new Parcelable.Creator<SavedState>() {
        public SavedState createFromParcel(Parcel in) { ... }
        public SavedState[] newArray(int size) { ... }
    };
}

屏幕方向更改时，在sufaceview上重绘路径

1 个答案: