计算android中画布上自定义线创建的形状面积

我正在制作一个建筑规划应用程序。在这里，我想通过drawline（）方法在画布上找到由线绘制的闭合形状所覆盖的区域。这是代码

public class CanvasBackground extends View {

public static boolean addPath;
public static flg flag;
public static boolean addLine = false;
public static boolean join = false;
public static boolean isDrawing;
public static int myLine;
public static ArrayList<Line> lines = new ArrayList<>();
public static ArrayList<Path> paths = new ArrayList<>();
public Paint paint;
public Context context;
public Canvas canvas;
public ScaleGestureDetector scaleGestureDetector;
public Bitmap addBtnBitmap;
public int passed_size;
float scalfactor = 1f;
Button addBtn;
public CanvasBackground(Context context) {
    super(context);
    this.context = context;
    paint = new Paint();
    scaleGestureDetector = new ScaleGestureDetector(context, new CanvasScale());
    DrawingActivity drawingActivity = new DrawingActivity();
    passed_size = drawingActivity.getCategory();


    setDrawingCacheEnabled(true);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    this.canvas = canvas;
    canvas.save();
    //add Button Select

    paint.setColor(Color.WHITE);
    canvas.drawPaint(paint);

    DrawingZoomingCanvas(canvas);
    DrawingLine(canvas);


    canvas.restore();
    Log.e("OnDraw >>>", "CALLING");
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            if (addLine) {
                if (lines.size() != 0) {
                    Line current = lines.get(lines.size() - 1);

                    lines.add(new Line(current.stopX, current.stopY, myLine));


                } else {

                    lines.add(new Line(event.getX(), event.getY(), myLine));
                }


                isDrawing = true;
                addLine = false;
            }

            if (addPath) {
                Path path = new Path();
                path.moveTo(event.getX(), event.getY());
                paths.add(path);
                isDrawing = true;
                addPath = false;
            }
            invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            if (isDrawing) {
                if (lines.size() > 0 && flg.ADDLINE == flag) {
                    Line current = lines.get(lines.size() - 1);
                    current.stopX = event.getX();
                    current.stopY = event.getY();
                } else if (paths.size() > 0 && flg.ADDPATH == flag) {
                    Path path = paths.get(paths.size() - 1);
                    path.lineTo(event.getX(), event.getY());
                }
                invalidate();
            }
            break;
        case MotionEvent.ACTION_UP:
            if (isDrawing) {
                if (lines.size() > 0 && flg.ADDLINE == flag) {
                    Line current = lines.get(lines.size() - 1);
                    current.stopX = event.getX();
                    current.stopY = event.getY();
                }
                invalidate();
            }
            break;
        default:
            break;
    }
    //scaleGestureDetector.onTouchEvent(event);

    Log.e("OnTouch >>>", "CALLING " + isDrawing + " >> " + event.getX() + " >> " + event.getY() + ">>" + event.getAction());
    return true;
}

//drawing a line
private void DrawingLine(Canvas canvas) {
    paint = new Paint();
    paint.setColor(Color.RED);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(2);
    paint.setAntiAlias(true);
    for (Line l : lines) {
        canvas.drawLine(l.startX, l.startY, l.stopX, l.stopY, paint);
        canvas.drawText(String.valueOf(l.getSize()), l.startX, l.startY, paint);
    }
    for (Path l : paths) {
        canvas.drawPath(l, paint);
    }
    if (flg.JOIN == flag) {
        Line first = lines.get(0);
        Line last = lines.get(lines.size() - 1);
        Log.e("FL", "First:-" + first.startX + first.startY + "Last" + last.stopX + last.stopY);
        canvas.drawLine(first.startX, first.startY, last.stopX, last.stopY, paint);
        canvas.drawText(String.valueOf(myLine), last.stopX, last.stopY, paint);
        invalidate();
        isDrawing = true;

    }
    setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            Log.e("CALL CLICK", "vv" + v.getId());
        }
    });

}

//drawing Matrix Canvas With Zoom
private void DrawingZoomingCanvas(Canvas canvas) {
    //drawing Matarix
    canvas.translate(scalfactor * 10, scalfactor * 10);
    canvas.scale(scalfactor, scalfactor);
    paint.setColor(Color.rgb(220, 220, 220));
    for (int i = 0; i <= canvas.getHeight() * scalfactor; i += 10) {
        canvas.drawLine(i, 0, i, canvas.getHeight(), paint);
        canvas.drawLine(0, i, canvas.getWidth(), i, paint);
    }
}

public void join_line() {

    Line first = lines.get(0);
    Line last = lines.get(lines.size() - 1);
    Log.e("FL", "First:-" + first.startX + first.startY + "Last" + last.stopX + last.stopY);
    canvas.drawLine(first.startX, first.startY, last.stopX, last.stopY, paint);
    invalidate();
    isDrawing = true;

}

public enum flg {ADDLINE, ADDPATH, JOIN}

private class CanvasScale extends ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        scalfactor *= scaleGestureDetector.getScaleFactor();
        scalfactor = Math.max(0.1f, Math.min(scalfactor, 10.0f));
        invalidate();
        return true;
    }
}

}

---

这就是全部代码。请帮助我。

Ya您可以首先通过观察开始和结束坐标来验证用户在触摸时形成的形状是否接近。一次，如果形状是闭合的。它形成一个正多边形

对于正多边形

求多边形的周长（permiter=所有边长的总和）

然后找到多边形的apothem（apothem=边的长度/2tan（180/边的数量））

它们使用周长和它们之间的距离来查找区域。（面积=（面积*周长）/2）

有关详细步骤的更多信息，请参阅此链接。

---

你知道计算形状面积的公式吗？如果您这样做了，请将其转换为Java。如果你没有-首先找到它，然后转换。你也可以使用搜索找到现成的解决方案。你完全正确。但是，绘制哪种形状并不是固定不变的。任何形状都有通用的公式，比如基山。。如果你觉得这个答案有用。请不要投这个答案。

public class DrawingActivity extends AppCompatActivity {
public int line_size;
CanvasBackground canvasBackground;
LinearLayout linearLayoutV, linearLayoutH;
Button addBtn, confirmBtn, clearBtn, addPath, joinbtn;
Context context = DrawingActivity.this;
LinearLayout.LayoutParams wrap_content_layoutParams = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);

@Override
protected void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    canvasBackground = new CanvasBackground(context);

    //Main Layout Liner
    linearLayoutV = new LinearLayout(context);
    linearLayoutV.setOrientation(LinearLayout.VERTICAL);

    linearLayoutH = new LinearLayout(context);
    linearLayoutH.setOrientation(LinearLayout.HORIZONTAL);
    linearLayoutH.setWeightSum(4);
    LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(10, ViewGroup.LayoutParams.WRAP_CONTENT);
    layoutParams.weight = 1;


    //add Line Button
    addBtn = new Button(context);
    addBtn.setLayoutParams(layoutParams);
    addBtn.setText("Line+");
    addBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            CanvasBackground.addLine = true;
            CanvasBackground.flag = CanvasBackground.flg.ADDLINE;

            //**************** SET LENGTH
            AlertDialog.Builder builder1 = new AlertDialog.Builder(context);
            builder1.setMessage("Set the length of line");
            builder1.setCancelable(true);
            final EditText input = new EditText(DrawingActivity.this);
            LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.MATCH_PARENT,
                    LinearLayout.LayoutParams.MATCH_PARENT);
            input.setLayoutParams(lp);
            builder1.setView(input);

            builder1.setPositiveButton(
                    "Done",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            line_size = Integer.parseInt(input.getText().toString());
                            Log.e("size", String.valueOf(getCategory()));
                            CanvasBackground.myLine = line_size;
                            dialog.cancel();
                        }
                    });

            builder1.setNegativeButton(
                    "Cancel",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            dialog.cancel();
                        }
                    });

            AlertDialog alert11 = builder1.create();
            alert11.show();
        }
    });
    linearLayoutH.addView(addBtn);
    // join last button
    joinbtn = new Button(context);
    joinbtn.setLayoutParams(layoutParams);
    joinbtn.setText("Join");
    joinbtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            CanvasBackground.flag = CanvasBackground.flg.JOIN;

            v.invalidate();
            //**************** SET LENGTH
            AlertDialog.Builder builder1 = new AlertDialog.Builder(context);
            builder1.setMessage("Set the length of line");
            builder1.setCancelable(true);
            final EditText input = new EditText(DrawingActivity.this);
            LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.MATCH_PARENT,
                    LinearLayout.LayoutParams.MATCH_PARENT);
            input.setLayoutParams(lp);
            builder1.setView(input);

            builder1.setPositiveButton(
                    "Done",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            line_size = Integer.parseInt(input.getText().toString());
                            Log.e("size", String.valueOf(getCategory()));
                            CanvasBackground.myLine = line_size;
                            dialog.cancel();
                        }
                    });

            builder1.setNegativeButton(
                    "Cancel",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            dialog.cancel();
                        }
                    });

            AlertDialog alert11 = builder1.create();
            alert11.show();

        }
    });
    linearLayoutH.addView(joinbtn);

    //add Line Button
    addPath = new Button(context);
    addPath.setLayoutParams(layoutParams);
    addPath.setText("Path+");
    addPath.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            CanvasBackground.addPath = true;
            CanvasBackground.flag = CanvasBackground.flg.ADDPATH;
        }
    });
    linearLayoutH.addView(addPath);



    //add Confirm Button
    confirmBtn = new Button(context);
    confirmBtn.setLayoutParams(layoutParams);
    confirmBtn.setText("Ok");
    confirmBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            CanvasBackground.isDrawing = false;
        }
    });
    linearLayoutH.addView(confirmBtn);
    linearLayoutV.addView(linearLayoutH);


    linearLayoutV.addView(canvasBackground);

    setContentView(linearLayoutV);
}

public int getCategory() {
    return line_size;
}

}