设置max＆amp;使用onDraw

Question

我的项目中有自定义视图。在视图类中，我使用onDraw方法绘制一条线。可以通过向上和向下滑动来改变线条的高度。如何设置该线条高度的最大值和最小值？

这是我的代码

 package com.example.richyrony.draw;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.graphics.RectF;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;

/**
 * Created by Richy & Rony on 26-01-2018.
 */

public class Line extends View {


    PointF topLeft = new PointF(100, 100);
    PointF topRight = new PointF(290, 100);
    PointF bottomLeft = new PointF(100, 290);
    PointF bottomRight = new PointF(290, 290);
    private final int NONE = -1, TOUCH_TOP_LEFT = 0, TOUCH_TOP_RIGHT = 1, TOUCH_BOT_LEFT = 2, TOUCH_BOT_RIGHT = 3;
    int currentTouch = NONE;

    Float lineTwoStartx = 250f;
    Float lineTwoStart = 50f;
    Float lineTwoEndx = 250f;
    Float lineTwoEnd = 200f;


    Float lineOneStartx = 50f;
    Float lineOneStart = 50f;
    ;
    Float lineOneEndx = 50f;
    Float lineOneEnd = 200f;

    RectF touchArea = new RectF(0, 0, 350, 350);
    Paint paint;

    public Line(Context context) {
        super(context);
        paint = new Paint();
        paint.setStrokeWidth(4);

        paint.setColor(Color.parseColor("#000000"));
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawLine(lineOneStartx, lineOneStart, lineOneEndx, lineOneEnd, paint);
        canvas.drawLine(lineTwoStartx, lineTwoStart, lineTwoEndx, lineTwoEnd, paint);
        canvas.drawLine(lineOneEndx, lineOneEnd, lineTwoEndx, lineTwoEnd, paint);
        canvas.drawLine(lineOneStartx, lineOneStart, lineTwoStartx, lineTwoStart, paint);


    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {

            //The user just put their finger down.
            //We check to see which corner the user is touching
            //And set our global, currentTouch, to the appropriate constant.
            case MotionEvent.ACTION_DOWN:
                if (touchArea.contains(event.getX(), event.getY())) {
                    currentTouch = TOUCH_TOP_LEFT;

                    Toast.makeText(getContext(), "tf" + currentTouch, Toast.LENGTH_SHORT).show();

                }   else {
                    return false; //Return false if user touches none of the corners
                }
                return true; //Return true if the user touches one of the corners
            //Now we know which corner the user is touching.
            //When the user moves their finger, we update the point to the user position and invalidate.
            case MotionEvent.ACTION_MOVE:
                switch (currentTouch) {
                    case TOUCH_TOP_LEFT:
                        lineOneEnd = event.getY();
                        invalidate();
                        return true;

                }
                //We returned true for all of the above cases, because we used the event
                return false; //If currentTouch is none of the above cases, return false

            //Here the user lifts up their finger.
            //We update the points one last time, and set currentTouch to NONE.
            case MotionEvent.ACTION_UP:
                switch (currentTouch) {
                    case TOUCH_TOP_LEFT:
                        lineOneEnd = event.getY(); 
                        currentTouch = NONE;
                        invalidate();
                        return true;

                }
                return false;
        }
        return false;
    }
}

如果有人知道如何测量两条线之间的角度，那将会很有帮助