Question

我想在视图上的点之间绘制线条，然后将这些点拉到所需位置，即使形状会发生变化。

我知道如何通过使用这个来绘制两点之间的线canvas.drawLine(10, 10, 90, 10, paint);我可以画点之间的线。

EDIT：在这里我附上图片以便清楚解释，从保罗回答我现在能够划分点之间的界线，仍然有拉点问题......

enter image description here

Answer 1

以下是它的完成方式。假设你有自己的观点，请将这些观点全局化：

PointF topLeft = new PointF(10,10);
PointF topRight = new PointF(90,10);
PointF bottomLeft = new PointF(10,90);
PointF bottomRight = new PointF(90,90);

您需要做的是围绕每个点制作一个RectF。 RectF越大，该点的触摸面积就越大。

float sizeOfRect = 5f;
RectF topLeftTouchArea = new RectF(topLeft.x - sizeOfRect, topLeft.y - sizeOfRect, topLeft.x + sizeOfRect, topLeft.y + sizeOfRect);
//Do this for the other points too

定义一些全局变量以跟踪用户在onTouch中的行为。一个int是被触摸的角落，另外四个是角落的标识符。

private final int NONE = -1, TOUCH_TOP_LEFT = 0, TOUCH_TOP_RIGHT = 1, TOUCH_BOT_LEFT = 2, TOUCH_BOT_RIGHT = 3;
int currentTouch = NONE;

现在，在onTouch事件中，您可以检查用户正在触摸的位置，如下所示：

@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 (topLeftTouchArea.contains(event.getX(), event.getY()) {
            currentTouch = TOUCH_TOP_LEFT;
        } else if (topRightTouchArea.contains(event.getX(),event.getY()) {
            currentTouch = TOUCH_TOP_RIGHT;
        } else if (botLeftTouchArea.contains(event.getX(),event.getY()) {
            currentTouch = TOUCH_BOT_LEFT;
        } else if (botRightTouchArea.contains(event.getX(), event.getY()) {
            currentTouch = TOUCH_BOT_RIGHT;
        } 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:
             topLeft.x = event.getX();
             topLeft.y = event.getY();
             //The bottom left x position has to move with the top left corner
             bottomLeft.x = topLeft.x;
             //The top right y position has to move with the top left corner
             topRight.y = topLeft.y;
             invalidate();
             return true;
        case TOUCH_TOP_RIGHT:
             topRight.x = event.getX();
             topRight.y = event.getY();
             //The top left y position has to move with the top right corner
             topLeft.y = topRight.y;
             //The bottom right x position has to move with the top right corner
             bottomRight.x = topRight.x;
             invalidate();
             return true;
        case TOUCH_BOT_LEFT:
             bottomLeft.x = event.getX();
             bottomLeft.y = event.getY();
             bottomRight.y = bottomLeft.y;
             topLeft.x = bottomLeft.x;
             invalidate();
             return true;
        case TOUCH_BOT_RIGHT:
             bottomRight.x = event.getX();
             bottomRight.y = event.getY();
             topRight.x = bottomRight.x;
             bottomLeft.y = bottomRight.y;
             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:
             topLeft.x = event.getX();
             topLeft.y = event.getY();
             //The bottom left x position has to move with the top left corner
             bottomLeft.x = topLeft.x;
             //The top right y position has to move with the top left corner
             topRight.y = topLeft.y;
             invalidate();
             currentTouch = NONE;
             return true;
        case TOUCH_TOP_RIGHT:
             topRight.x = event.getX();
             topRight.y = event.getY();
             //The top left y position has to move with the top right corner
             topLeft.y = topRight.y;
             //The bottom right x position has to move with the top right corner
             bottomRight.x = topRight.x;
             invalidate();
             currentTouch = NONE;
             return true;
        case TOUCH_BOT_LEFT:
             bottomLeft.x = event.getX();
             bottomLeft.y = event.getY();
             bottomRight.y = bottomLeft.y;
             topLeft.x = bottomLeft.x;
             invalidate();
             currentTouch = NONE;
             return true;
        case TOUCH_BOT_RIGHT:
             bottomRight.x = event.getX();
             bottomRight.y = event.getY();
             topRight.x = bottomRight.x;
             bottomLeft.y = bottomRight.y;
             invalidate();
             currentTouch = NONE;
             return true;
        }
        return false;
    }
}

这样做会在你的观点周围形成一个矩形。想象一下在图片中的点周围绘制框。这些是由Rect对象创建的“触摸板”。矩形的大小由sizeOfRect设置。在onTouchEvent中，它检查每个矩形对象以查看用户的触摸是否在矩形内，表示用户试图触摸该点。

Answer 2

我想您可能正在寻找Path课程：

Path类封装了复合（多个轮廓）几何由直线段，二次曲线和三次曲线。它可以用canvas.drawPath（path，paint）绘制，填充或抚摸（基于油漆的样式），或者它可以用于剪辑或在路径上绘制文字。

有关canvas.drawPath

的示例，请参阅this tutorial

Answer 3

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.PointF;
import android.view.MotionEvent;
import android.view.View;

public class TestView extends View
{

    private Paint paint;
    private PointF startPoint, endPoint;
    private boolean isDrawing;

    public TestView(Context context)
    {
        super(context);
        init();
    }

    private void init()
    {
        paint = new Paint();
        paint.setColor(Color.RED);
        paint.setStyle(Style.STROKE);
        paint.setStrokeWidth(2);
        paint.setAntiAlias(true);
    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        if(isDrawing)
        {
            canvas.drawLine(startPoint.x, startPoint.y, endPoint.x, endPoint.y, paint);
        }
    }


    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        switch (event.getAction())
        {
            case MotionEvent.ACTION_DOWN:
                startPoint = new PointF(event.getX(), event.getY());
                endPoint = new PointF();
                isDrawing = true;
                break;
            case MotionEvent.ACTION_MOVE:
                if(isDrawing)
                {
                    endPoint.x = event.getX();
                    endPoint.y = event.getY();
                    invalidate();
                }
                break;
            case MotionEvent.ACTION_UP:
                if(isDrawing)
                {
                    endPoint.x = event.getX();
                    endPoint.y = event.getY();
                    isDrawing = false;
                    invalidate();
                }
                break;
            default:
                break;
        }
        return true;
    }
}

Answer 4

编辑：

你确实需要在android中使用Path类。抱歉，我无法想出代码段。但这是让你开始的东西。

当您画一条线 - canvas.drawLine(x1, y1, x2, y2, paint);时，您的起点是(x1,y1)。现在，如果你需要从任何一端拉线，你需要先修复另一端。假设您从(x2,y2)开始。所以(x1,y1)变得不变，你从另一端拉出来。使用Path类时，首先调用moveTo()到此修复点。它的作用是给出一个关于必须移动线的点。然后，您可以使用触摸事件上的lineTo()调用来相应地拉伸线条。需要进行大量调整。但这可以让你开始。对不起，我无法想出一个片段，时间不够短。请参阅Path类的文档。你可能会发现一些更有用的东西。

编辑：

关于向点添加触摸侦听器：

假设您有一行(x1,y1)到(x2,y2)。

现在要获得某个点的触控侦听器，您可以在整个视图中添加onTouchListener。

final View touchView = findViewById(R.id.touchView);
    touchView.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
               if(event.getX() == x2 && event.getY() == y2)
               {
                  //you know that you have clicked on the rear end of the line,so now you can do your dragging stuff.
                  if(event.getAction() == MotionEvent.ACTION_DOWN){
                       //you know user has clicked in order to draw
                       //redraw the existing line with black color to remove it
                       paint.setColor(Color.BLACK);
                       canvas.drawLine(x1, y1, x2, y2, paint);
                       //reset the paint object
                       paint.setColor(Color.WHITE); 
                       //now use moveTo() and lineTo() to attain the functionality of dragging on your Path object
                       path.moveTo(x1,y1);
                       path.lineTo(event.getX(),event.getY());
                  }else if(event.getAction() == MotionEvent.ACTION_MOVE){
                       path.lineTo(event.getX(),event.getY());
                  }else if(event.getAction() == MotionEvent.ACTION_UP){
                  }
       }  
               return true;
        }
    });

这只是一个想法，我仍然没有机会测试它。我希望它有所帮助。

如何在点之间画线并拉出这些点？

4 个答案: