首先新建一个项目工程，建立文件，如下图所示

首先配置页面布局文件activity_main.xml，如下图所示：

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical">

android:id="@+id/iv"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:background="@drawable/bg"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="画笔的粗细"

/>

android:id="@+id/sb"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:max="256"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="颜色"

/>

android:id="@+id/sp"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:entries="@array/color"

/>

android:id="@+id/btn"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="保存"

/>

然后书写主页的代码MainActivity.java代码如下

package com.xunfang.drawing;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import android.app.Activity;

import android.content.Intent;

import android.graphics.Bitmap;

import android.graphics.Bitmap.CompressFormat;

import android.graphics.BitmapFactory;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Matrix;

import android.graphics.Paint;

import android.net.Uri;

import android.os.Bundle;

import android.os.Environment;

import android.util.MonthDisplayHelper;

import android.view.Menu;

import android.view.MenuItem;

import android.view.MotionEvent;

import android.view.View;

import android.view.View.OnClickListener;

import android.view.View.OnTouchListener;

import android.widget.AdapterView;

import android.widget.AdapterView.OnItemClickListener;

import android.widget.AdapterView.OnItemSelectedListener;

import android.widget.Button;

import android.widget.ImageView;

import android.widget.SeekBar;

import android.widget.Spinner;

import android.widget.Toast;

public class MainActivity extends Activity {

private SeekBar sb;

private ImageView iv;

private Button btn;

private Spinner sp;

private String[] color ;

private Bitmap bm;

private Bitmap copy;

private Canvas canvas;

private Paint paint;

private File file;

private int yanse;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

//拿到在xml文件中定义的颜色数组

color = getResources().getStringArray(R.array.color) ;

//实例化

initData();

//设置监听器

setLister();

//画画

loadingImage();

}

private void loadingImage() {

// 加载原始图片

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

// 需要创建一个和原始的图片大小一样的空白图片(一张纸,上面没有任何数据)

copy = bm.createBitmap(bm.getWidth(), bm.getHeight(), bm.getConfig());

// 需要一个画板,画板上铺上白纸

canvas= new Canvas(copy);

// 创建画笔

paint= new Paint();

// 给imageView空间加载一个滑动监听器

iv.setOnTouchListener(new OnTouchListener() {

int startx;

int starty;

@Override

public boolean onTouch(View v, MotionEvent event) {

// 拿到动作

int type = event.getAction();

switch (type) {

case MotionEvent.ACTION_DOWN:

startx = (int) event.getX();

starty = (int) event.getY();

break;

case MotionEvent.ACTION_MOVE:

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

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

//画画

canvas.drawLine(startx, starty, endx, endy, paint);

startx = (int) event.getX();

starty = (int) event.getY();

iv.setImageBitmap(copy);

break;

case MotionEvent.ACTION_UP:

break;

}

return true;

}

});

}

private void setLister() {

//下拉框

sp.setOnItemSelectedListener(new OnItemSelectedListener() {

@Override

public void onItemSelected(AdapterView<?> parent, View view,

int position, long id) {

Toast.makeText(getApplicationContext(), "你点击的是：" + color[position], 0).show();

switch (position) {

case 1:

paint.setColor(Color.GREEN);

break;

case 2:

paint.setColor(Color.BLUE);

break;

case 3:

paint.setColor(Color.BLACK);

break;

case 4:

paint.setColor(Color.YELLOW);

break;

case 0:

paint.setColor(Color.RED);

break;

}

}

@Override

public void onNothingSelected(AdapterView<?> parent) {

}

});

//保存

btn.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

try {

//指定图片的存储路径

file = new File(Environment.getExternalStorageDirectory().getAbsoluteFile()+"/draw.png");

FileOutputStream fos = new FileOutputStream(file);

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

Toast.makeText(getApplicationContext(), "保存成功", 0).show() ;

} catch (Exception e) {

}

//欺骗系统,告诉系统插入一个sd卡

Intent intent = new Intent();

intent.setAction(intent.ACTION_MEDIA_MOUNTED);

intent.setData(Uri.fromFile(file));

sendBroadcast(intent);

}

});

}

private void initData() {

sb = (SeekBar) findViewById(R.id.sb);

btn = (Button) findViewById(R.id.btn);

sp = (Spinner) findViewById(R.id.sp);

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

}

}

AndroidManifest.xml配置文件如下：

package="com.xunfang.drawing"

android:versionCode="1"

android:versionName="1.0" >

android:minSdkVersion="16"

android:targetSdkVersion="21" />

android:allowBackup="true"

android:icon="@drawable/ic_launcher"

android:label="@string/app_name"

android:theme="@style/AppTheme" >

android:name=".MainActivity"

android:label="@string/app_name" >

然后用虚拟机测试如下所示：

可以在模拟器看一下，生成的文件

表示验证成功了