Android 实现手绘功能教程

布局文件如下。

activity代码如下，其中线的颜色，宽度等属性都可以修改。

package com.example.administrator.main;

import android.content.intent;
import android.graphics.bitmap;
import android.graphics.canvas;
import android.graphics.color;
import android.graphics.paint;
import android.net.uri;
import android.os.environment;
import android.support.v7.app.appcompatactivity;
import android.os.bundle;
import android.view.motionevent;
import android.view.view;
import android.widget.button;
import android.widget.imageview;
import android.widget.toast;

import java.io.file;
import java.io.fileoutputstream;

public class drawactivity extends appcompatactivity {
 private imageview iv;
 private bitmap basebitmap;
 private button btn_resume;
 private button btn_save;
 private canvas canvas;
 private paint paint;

 float radio;

 @override
 protected void oncreate(bundle savedinstancestate) {
  super.oncreate(savedinstancestate);
  setcontentview(r.layout.activity_draw);
  radio = 10;
  iv = (imageview) findviewbyid(r.id.iv);
  // 初始化一个画笔，笔触宽度为5，颜色为红色
  paint = new paint();
  paint.setstrokewidth(radio);
  paint.setcolor(color.black);
  iv = (imageview) findviewbyid(r.id.iv);
  btn_resume = (button) findviewbyid(r.id.btn_resume);
  btn_save = (button) findviewbyid(r.id.btn_save);

  btn_resume.setonclicklistener(click);
  btn_save.setonclicklistener(click);
  iv.setontouchlistener(touch);
 }

 private view.ontouchlistener touch = new view.ontouchlistener() {
  // 定义手指开始触摸的坐标
  float startx;
  float starty;

  @override
  public boolean ontouch(view v, motionevent event) {
switch (event.getaction()) {
 // 用户按下动作
 case motionevent.action_down:
  // 第一次绘图初始化内存图片，指定背景为白色
  if (basebitmap == null) {
basebitmap = bitmap.createbitmap(iv.getwidth(),
  iv.getheight(), bitmap.config.argb_8888);
canvas = new canvas(basebitmap);
canvas.drawcolor(color.white);
  }
  // 记录开始触摸的点的坐标
  startx = event.getx();
  starty = event.gety();
  break;
 // 用户手指在屏幕上移动的动作
 case motionevent.action_move:
  // 记录移动位置的点的坐标
  float stopx = event.getx();
  float stopy = event.gety();

  thread t = new thread(new runnable() {
@override
public void run() {
 radio += 0.1;

 try {
  thread.sleep(1000);
 } catch (interruptedexception e) {
  e.printstacktrace();
 }
}
  });
  t.start();

  paint.setstrokewidth(radio);
  //根据两点坐标，绘制连线
  canvas.drawline(startx, starty, stopx, stopy, paint);

  // 更新开始点的位置
  startx = event.getx();
  starty = event.gety();
  // 把图片展示到imageview中
  iv.setimagebitmap(basebitmap);
  break;
 case motionevent.action_up:
  radio = 5;
  break;
 default:
  break;
}
return true;
  }
 };
 private view.onclicklistener click = new view.onclicklistener() {

  @override
  public void onclick(view v) {
switch (v.getid()) {
 case r.id.btn_save:
  savebitmap();
  break;
 case r.id.btn_resume:
  resumecanvas();
  break;
 default:
  break;
}
  }
 };

 /**
  * 保存图片到sd卡上
  */
 protected void savebitmap() {
  try {
// 保存图片到sd卡上
string filename = "/sdcard/"+system.currenttimemillis() + ".png";
file file = new file(filename);
fileoutputstream stream = new fileoutputstream(file);
basebitmap.compress(bitmap.compressformat.png, 100, stream);
toast.maketext(drawactivity.this, "保存图片成功", toast.length_short).show();
 // android设备gallery应用只会在启动的时候扫描系统文件夹
 // 这里模拟一个媒体装载的广播，用于使保存的图片可以在gallery中查看
intent intent = new intent();
intent.setaction(intent.action_media_mounted);
intent.setdata(uri.fromfile(environment
  .getexternalstoragedirectory()));
sendbroadcast(intent);
  } catch (exception e) {
toast.maketext(drawactivity.this, "保存图片失败", toast.length_short).show();
e.printstacktrace();
  }
 }

 // 手动清除画板的绘图，重新创建一个画板
 protected void resumecanvas() {
  if (basebitmap != null) {
basebitmap = bitmap.createbitmap(iv.getwidth(),
  iv.getheight(), bitmap.config.argb_8888);
canvas = new canvas(basebitmap);
canvas.drawcolor(color.white);
iv.setimagebitmap(basebitmap);
toast.maketext(drawactivity.this, "清除画板成功，可以重新开始绘图", toast.length_short).show();
  }
 }
}