简单写字板

效果图：












package com.whzg.zbjy.homepage;

import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.net.Uri;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.whzg.zbjy.R;

import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;

public class CopyActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private TextView clear;
    private Bitmap baseBitmap;
    private ImageView iv;
    private Canvas canvas;
    private Paint paint;
    private VelocityTracker mVelocityTracker;
    private float velocityX, velocityY;
    private int i = 40, j = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_copy);
        toolbar = (Toolbar) findViewById(R.id.homepager_copy_toolbar);
        toolbar.setNavigationIcon(R.drawable.back);
        toolbar.setTitle("");
        toolbar.setSubtitle("返回");
        setSupportActionBar(toolbar);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                CopyActivity.this.finish();
            }
        });

        clear = (TextView) findViewById(R.id.homepager_copy_clear);
        clear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 创建一张空白图片
                baseBitmap = Bitmap.createBitmap(getWindowManager().getDefaultDisplay().getWidth(), getWindowManager().getDefaultDisplay().getHeight(), Bitmap.Config.ARGB_8888);
                // 创建一张画布
                canvas = new Canvas(baseBitmap);
                iv.setImageBitmap(baseBitmap);
            }
        });

        iv = (ImageView) this.findViewById(R.id.homepager_copy_img);

        // 创建一张空白图片
        baseBitmap = Bitmap.createBitmap(getWindowManager().getDefaultDisplay().getWidth(), getWindowManager().getDefaultDisplay().getHeight(), Bitmap.Config.ARGB_8888);
        // 创建一张画布
        canvas = new Canvas(baseBitmap);
        // 创建画笔
        paint = new Paint();
        paintSet(30, 255);
        // 先将灰色背景画上
        canvas.drawBitmap(baseBitmap, new Matrix(), paint);
        iv.setImageBitmap(baseBitmap);

        iv.setOnTouchListener(new View.OnTouchListener() {
            int startX;
            int startY;

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        // 获取手按下时的坐标
                        startX = (int) event.getX();
                        startY = (int) event.getY();
                        break;
                    case MotionEvent.ACTION_UP:
                        i = 40;
                        j = 0;
                        break;
                    case MotionEvent.ACTION_MOVE:
                        if (mVelocityTracker == null) {
                            mVelocityTracker = VelocityTracker.obtain();//获得VelocityTracker类实例
                        }
                        mVelocityTracker.addMovement(event);//将事件加入到VelocityTracker类实例中

                        mVelocityTracker.computeCurrentVelocity(1);
                        velocityX = mVelocityTracker.getXVelocity();
                        velocityY = mVelocityTracker.getXVelocity();

                        float xyv = velocityX * velocityX + velocityY * velocityY;
                        xyv = (float) Math.sqrt(xyv);
                        for (; j < 5; j++) {
                            if (Math.abs(xyv) < 0.4) {
                                continue;
                            } else {
                                j = 0;
                                break;
                            }
                        }
                        if (Math.abs(xyv) <= 3 && j == 0) {
                            i = (i * 1 - 1) / 1;
                        }
                        if (j != 0) {
                            i = (i * 1 - 1) / 1;
                            j = 0;
                        }
                        if (Math.abs(xyv) > 3 ){

                            i = (i * 1 + 1) / 1;
                            if (i>=40){
                                i=40;
                            }
                        }
                        paintSet(i, 255);
                        if (i <= 0) {
                            paintSet(i, 0);
                        }
                        // 获取手移动后的坐标
                        int stopX = (int) event.getX();
                        int stopY = (int) event.getY();
                        // 在开始和结束坐标间画一条线
                        canvas.drawLine(startX, startY, stopX, stopY, paint);
                        // 实时更新开始坐标
                        startX = (int) event.getX();
                        startY = (int) event.getY();
                        iv.setImageBitmap(baseBitmap);
                        break;
                }
                return true;
            }
        });

    }


    /**
     * 重设画笔
     *
     * @param width 画笔宽度
     * @param alpha 画笔透明度
     */
    public void paintSet(int width, int alpha) {

        paint.setColor(getResources().getColor(R.color.black));
        //消除锯齿
        paint.setAntiAlias(true);
        paint.setTextSize(20);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(width);
        paint.setStrokeCap(Paint.Cap.ROUND);
        paint.setAlpha(alpha);
    }


    public void save(View view) {
        try {
            File file = new File(Environment.getExternalStorageDirectory(),
                    System.currentTimeMillis() + ".jpg");
            OutputStream stream = new FileOutputStream(file);
            baseBitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream);
            stream.close();
            // 模拟一个广播，通知系统sdcard被挂载
            Intent intent = new Intent();
            intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
            intent.setData(Uri.fromFile(Environment
                    .getExternalStorageDirectory()));
            sendBroadcast(intent);

            Toast.makeText(this, "保存图片成功", Toast.LENGTH_LONG).show();
        } catch (Exception e) {
            Toast.makeText(this, "保存图片失败", Toast.LENGTH_LONG).show();
            e.printStackTrace();
        }
    }

}