自定义控件画板

自定义控件分为三类
自绘式自定义控件 组合式自定义控件 继承式自定义控件
每一个自定义控件都要重写的方法有

 public Base(Context context) {
        this(context,null);
    }

    public Base(Context context,  AttributeSet attrs) {
        super(context, attrs,0);
    }

    public Base(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

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

接下来进来画板的小Demo 没有撤销

package com.lichao.bwei.com.huaban;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class MainActivity extends AppCompatActivity {

    private ImageView mImageView;
    private Bitmap mCopyBitmap;
    private Paint mPaint;
    private Canvas mCanvas;
    private float startX;
    private float startY;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mImageView = findViewById(R.id.iv_image);
        //使用bitmap工厂吧图片加载进来
        Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
       //创建一个空的图片，宽度和长度还有消息跟图片一样
        mCopyBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());
       //创建画笔
        mPaint = new Paint();
        //创建画布
        mCanvas = new Canvas(mCopyBitmap);
        //开始画画
        mCanvas.drawBitmap(bitmap,new Matrix(),mPaint);
        mImageView.setImageBitmap(mCopyBitmap);

        mImageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                //获取动作的事件
                int action = event.getAction();
                switch (action) {
                    case MotionEvent.ACTION_DOWN:
                        //按下事件
                        startX = event.getX();
                        startY = event.getY();
                        Log.e("按下", startX + "," + startY);
                        break;
                    case MotionEvent.ACTION_MOVE:
                        //滑动事件
                        float x = event.getX();
                        float y = event.getY();
                        //在画布上画直线，不能画点，滑动事件获得的坐标不是连续的
                        mCanvas.drawLine(startX, startY, x, y, mPaint);
                        //更新图片
                        mImageView.setImageBitmap(mCopyBitmap);
                        startX = x;
                        startY = y;
                        Log.e("滑动", x + "," + y);
                        break;
                    case MotionEvent.ACTION_UP:
                        //抬起事件
                        float upX = event.getX();
                        float upY = event.getY();
                        Log.e("抬起", upX + "," + upY);
                        break;
                }
                //必须设置为true，否则只执行按下事件
                return true;
            }
        });

    }
    //修改画笔的颜色
    public void changeColor(View view) {
        mPaint.setColor(Color.RED);
    }

    //设置画笔的粗细
    public void bold(View view) {
        mPaint.setStrokeWidth(50);
    }

    //保存图片
    public void save(View view) {
        //创建一个图片的文件
        File file = new File(Environment.getExternalStorageDirectory(), System.currentTimeMillis() + ".png");
        FileOutputStream straeam;
        try {
            straeam = new FileOutputStream(file);
            //生成图片，参数①为图片的类型，参数②为图片质量，参数③为文件输出流
            mCopyBitmap.compress(Bitmap.CompressFormat.PNG, 100, straeam);
            Toast.makeText(this, "保存成功", Toast.LENGTH_SHORT).show();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="horizontal">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="bold"
            android:text="变粗" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="changeColor"
            android:text="改变颜色" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="save"
            android:text="保存图片" />


    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true">

        <ImageView
            android:id="@+id/iv_image"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/bg" />
    </LinearLayout>

</RelativeLayout>