class MainActivity

package com.example.choi.mystudy14;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    CustomView customView=null;
    Button newCanvasBtn, btn1;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        customView=(CustomView)findViewById(R.id.customView);
        customView.setmContext(MainActivity.this);



        newCanvasBtn=(Button)findViewById(R.id.bt_new_canvas);
        newCanvasBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                customView.initPaint(CustomView.NEW_CANVAS);
            }
        });

        //선굵기 체인지
        final EditText numberPic=(EditText)findViewById(R.id.numberPic);
        btn1=(Button)findViewById(R.id.btn1);
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                customView.mStrokeWidth=Integer.parseInt(numberPic.getText().toString());

                Toast.makeText(MainActivity.this, "변경되었습니다.", Toast.LENGTH_SHORT).show();
            }
        });


    }


}

 

R.layout.activity_main

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.choi.mystudy14.MainActivity">

    <com.example.choi.mystudy14.CustomView
        android:text="TextView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="9"
        android:id="@+id/customView"
        />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:orientation="horizontal"
        android:layout_weight="1"
        >


        <EditText
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:id="@+id/numberPic"
            android:layout_weight="2"
            android:inputType="number"
            android:maxLength="2"
            />

        <Button
            android:id="@+id/btn1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:text="선굵기변경"
            android:background="@android:color/holo_orange_dark"
            android:textAllCaps="false"
            android:textColor="@android:color/background_light" />

        <Button
            android:id="@+id/bt_new_canvas"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="6"
            android:text="New Canvas"
            android:background="@android:color/holo_green_dark"
            android:textAllCaps="false"
            android:textColor="@android:color/background_light" />

    </LinearLayout>


</LinearLayout>

 

class CustomView

package com.example.choi.mystudy14;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;

/**
 * Created by choi on 2017-03-05.
 */

public class CustomView extends View {

    public final static int START_CANVAS=0;
    public final static int NEW_CANVAS=1;


    private Context mContext;
    ArrayList<Dot> dots=new ArrayList<>();
    private Paint paint;
    int mStrokeWidth = 2; // 시작 선 두께


    public CustomView(Context context) {
        super(context);
        initPaint(START_CANVAS);
    }


    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initPaint(START_CANVAS);
    }

    public CustomView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initPaint(START_CANVAS);
    }



    public void setmContext(Context mContext) {
        this.mContext = mContext;
        initPaint(START_CANVAS);
    }


    public void initPaint(int i){
        dots.clear();
        paint=null;
        paint=new Paint();
        paint.setColor(Color.GREEN);
        paint.setStrokeWidth(mStrokeWidth);
        paint.setAntiAlias(true);

        if(i==CustomView.NEW_CANVAS) invalidate();;
    }



    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(Color.WHITE);

        //선굵기 체인지
        paint.setStrokeWidth(mStrokeWidth);

        for(int i=0; i<dots.size(); i++){
            Dot now =dots.get(i); //현재 좌표
            if(now.isDraw()){
                Dot before =dots.get(i-1);//이전좌표
                canvas.drawLine(before.getX(), before.getY(), now.getX(), now.getY(), paint);
            }
        }
    }



    @Override
    public boolean onTouchEvent(MotionEvent event) {

        //처음 터치 할때
        if(event.getAction()==MotionEvent.ACTION_DOWN){
            dots.add(new Dot(event.getX(), event.getY(), false));
            return true;
        }

        //터치한 상태에서 손가락을 움직일 때
        if(event.getAction()==MotionEvent.ACTION_MOVE){
            dots.add(new Dot(event.getX(), event.getY(), true));
            invalidate();
            return true;
        }


        return false;
    }




}

 

 

 

class Dot

package com.example.choi.mystudy14;

/**
 * Created by choi on 2017-03-05.
 */

public class Dot {

    float x, y;
    boolean isDraw;


    public Dot(float x, float y, boolean isDraw) {
        this.x = x;
        this.y = y;
        this.isDraw = isDraw;
    }

    public float getX() {
        return x;
    }

    public void setX(float x) {
        this.x = x;
    }

    public float getY() {
        return y;
    }

    public void setY(float y) {
        this.y = y;
    }

    public boolean isDraw() {
        return isDraw;
    }

    public void setDraw(boolean draw) {
        isDraw = draw;
    }

    @Override
    public String toString() {
        return "Dot{" +
                "x=" + x +
                ", y=" + y +
                ", isDraw=" + isDraw +
                '}';
    }
}