画画板

Posted 2020-08-31 SoulCode

#画画板（掌握）

>记录用户触摸事件的XY坐标，绘制直线

* 给ImageView设置触摸侦听，得到用户的触摸事件，并获知用户触摸ImageView的坐标

 

iv.setOnTouchListener(new OnTouchListener() {

 

@Override

public boolean onTouch(View v, MotionEvent event) {

// TODO Auto-generated method stub

switch (event.getAction()) {

//触摸屏幕

case MotionEvent.ACTION_DOWN:

//得到触摸屏幕时手指的坐标

startX = (int) event.getX();

startY = (int) event.getY();

break;

//在屏幕上滑动

case MotionEvent.ACTION_MOVE:

//用户滑动手指，坐标不断的改变，获取最新坐标

int newX = (int) event.getX();

int newY = (int) event.getY();

//用上次onTouch方法得到的坐标和本次得到的坐标绘制直线

canvas.drawLine(startX, startY, newX, newY, paint);

iv.setImageBitmap(copyBm);

startX = newX;

startY = newY;

break;

 

}

return true;

}

});

* 刷子效果，加粗画笔

 

paint.setStrokeWidth(8);

* 调色板，改变画笔颜色

 

paint.setColor(Color.GREEN);

* 保存图片至SD卡

 

FileOutputStream fos = null;

try {

fos = new FileOutputStream(new File("sdcard/dazuo.png"));

} catch (FileNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

//保存图片

     copyBm.compress(CompressFormat.PNG, 100, fos);

* 系统每次收到SD卡就绪广播时，都会去遍历sd卡的所有文件和文件夹，把遍历到的所有多媒体文件都在MediaStore数据库保存一个索引，这个索引包含多媒体文件的文件名、路径、大小

* 图库每次打开时，并不会去遍历sd卡获取图片，而是通过内容提供者从MediaStore数据库中获取图片的信息，然后读取该图片

* 系统开机或者点击加载sd卡按钮时，系统会发送sd卡就绪广播，我们也可以手动发送就绪广播

 

Intent intent = new Intent();

     intent.setAction(Intent.ACTION_MEDIA_MOUNTED);

     intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));

     sendBroadcast(intent);

 

源代码：

package com.itheima.paintboard;

 

import java.io.File;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

 

import android.net.Uri;

import android.os.Bundle;

import android.os.Environment;

import android.app.Activity;

import android.content.Intent;

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.graphics.Bitmap.CompressFormat;

import android.view.Menu;

import android.view.MotionEvent;

import android.view.View;

import android.view.View.OnTouchListener;

import android.widget.ImageView;

 

public class MainActivity extends Activity {

private int startX;

private int startY;

private Paint paint;

private Canvas canvas;

private ImageView iv;

private Bitmap bmCopy;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

 

Bitmap bmSrc = BitmapFactory.decodeResource(getResources(), R.drawable.bg);

//白纸

bmCopy = Bitmap.createBitmap(bmSrc.getWidth(), bmSrc.getHeight(), bmSrc.getConfig());

//笔

paint = new Paint();

//画板

canvas = new Canvas(bmCopy);

//作画

canvas.drawBitmap(bmSrc, new Matrix(), paint);

 

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

iv.setImageBitmap(bmCopy);

 

iv.setOnTouchListener(new OnTouchListener() {

 

//用户手指只要触摸屏幕，就会产生触摸事件

@Override

public boolean onTouch(View v, MotionEvent event) {

//判断触摸事件的类型

switch (event.getAction()) {

//手指触摸

case MotionEvent.ACTION_DOWN:

//触摸事件中会包含手指触摸的坐标

startX = (int) event.getX();

startY = (int) event.getY();

break;

//手指滑动

case MotionEvent.ACTION_MOVE:

int newX = (int) event.getX();

int newY = (int) event.getY();

//指定线的起点和终点

canvas.drawLine(startX, startY, newX, newY, paint);

 

//刷新,因为每次滑动绘画时，图片保存在缓存里，所以需要重新设置ImageView进行刷新到界面上

 

 

iv.setImageBitmap(bmCopy);

 

//把本此画线的终点设置为下一次画线的起点

startX = newX;

startY = newY;

break;

//手指抬起

case MotionEvent.ACTION_UP:

break;

 

}

//true表示告诉系统，这个触摸事件由iv处理

//false表示不处理该触摸事件，事件往上传递

return true;

}

});

}

 

public void red(View v){

paint.setColor(Color.RED);

}

 

public void green(View v){

paint.setColor(Color.GREEN);

}

 

public void brush(View v){

//改变线条粗细

paint.setStrokeWidth(8);

}

 

public void save(View v){

File file = new File("sdcard/dazuo.png");

FileOutputStream fos;

try {

fos = new FileOutputStream(file);

//把图片压缩到本地文件

bmCopy.compress(CompressFormat.PNG, 100, fos);

fos.close();

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

 

//手动发一个sd卡就绪广播

Intent intent = new Intent();

intent.setAction(Intent.ACTION_MEDIA_MOUNTED);

intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));

sendBroadcast(intent);

}

 

 

}