画梯形，单独放大或缩小x轴方向，y轴方向；同时放大或缩小x、y轴方向

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package com.fpt.enlargeview;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class EnlargeOntouchView extends View{
    private Paint paint;
    private Path path;
    private int x1,y1,x2,y2,x3,y3,x4,y4;
    private int[] move1,move2;
    private int lengx,lengy,baselength,length,lengx1,lengy1,lengx2,lengy2;
    private int rang=30;
    public EnlargeOntouchView(Context context) {
        super(context);
        initData();
    }

    public EnlargeOntouchView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        initData();
    }

    public EnlargeOntouchView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initData();
    }

    public EnlargeOntouchView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        initData();
    }

    public void initData(){
        paint=new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(2);
        paint.setColor(Color.BLACK);
        path=new Path();
        x1=60;y1=500;
        x2=40;y2=700;
        x3=240;y3=500;
        x4=260;y4=700;

    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);


        path.reset();
        path.moveTo(x1,y1);
        path.lineTo(x2,y2);
        path.lineTo(x4,y4);
        path.lineTo(x3,y3);
        path.close();
        canvas.drawPath(path,paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()){
            case MotionEvent.ACTION_MOVE:
                if (event.getPointerCount()==2){//该判断放到down中，是监听不了的，只有这个地方可以监听
                    if (baselength==0) {
                        move1 = new int[]{(int) event.getX(0), (int) event.getY(0)};
                        move2 = new int[]{(int) event.getX(1), (int) event.getY(1)};
                        lengx = Math.abs(move2[0] - move1[0]);
                        lengy = Math.abs(move2[1] - move1[1]);
                        lengx1=move2[0]-move1[0];
                        lengy1=move2[1]-move1[1];
                        baselength = (int) Math.sqrt(lengx * lengx + lengy * lengy);
                        Log.e("event", "baselength:" + baselength);
                    }else {
                        move1 = new int[]{(int) event.getX(0), (int) event.getY(0)};
                        move2 = new int[]{(int) event.getX(1), (int) event.getY(1)};
                        lengx = Math.abs(move2[0] - move1[0]);
                        lengy = Math.abs(move2[1] - move1[1]);
                        lengx2=move2[0]-move1[0];
                        lengy2=move2[1]-move1[1];
                        length = (int) Math.sqrt(lengx * lengx + lengy * lengy);
                        length=length-baselength;
                        if (length<0){//缩小
                            if (((lengy1-lengy2)<lengy+rang)&&((lengy1-lengy2)>lengy-rang)){//调整x轴
                                
                                updataCoorida((-1*3),0);//缩小时，当y轴没有改变时
                            }else if ((lengx-rang<(lengx1-lengx2))&&((lengx1-lengx2)<lengx+rang)){
                                updataCoorida(0,(-1*3));//缩小时，当x轴没有变化时
                            }else {
                                updataCoorida((-1*3),(-1*3));//缩小时，当x，y都有变化时
                            }
//                            updataCoorida(-1*3);//*3表示加速级别
                        }else {
                            if ((lengy1-lengy2)<lengy+rang&&((lengy1-lengy2)>lengy-rang)){
                                updataCoorida((1*3),0);//扩大时，当y轴没有变化时
                            }else if ((lengx1-lengx2)<lengx+rang&&(lengx1-lengx2)>lengx-rang){
                                updataCoorida(0,(1*3));//扩大时，当x轴没有变化时
                            }else {
                                updataCoorida((1*3),(1*3));//扩大时，当x，y轴同时变化时。
                            }
//                            updataCoorida(1*3);//*3表示加速级别
                        }
                        Log.e("event", "length:" + length);
                        baselength=0;//画龙点睛，精彩
                    }
                }

                break;
            case MotionEvent.ACTION_UP:
                length=0;
                break;
        }
        return true;
    }
    public void updataCoorida(int number,int number2){
        this.x1=x1-number;
        this.x2=x2-number;
        this.x3=x3+number;
        this.x4=x4+number;
        this.y1=y1-number2;
        this.y3=y3-number2;
        this.y2=y2+number2;
        this.y4=y4+number2;
        invalidate();//重新调用onDraw
    }

}