Android——课堂整理：assets目录和手机外部存储

layout文件：

 <Button
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="保存资产文件到内部存储"
         android:onClick="bt4_onClick"/>
     <ImageView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:id="@+id/iv_1"
         android:src="@drawable/on"/>
     <Button
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="设置图片指向内部存储"
         android:onClick="bt5_onClick"/>
     <Button
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="写入外部存储文件"
         android:onClick="bt6_onClick"/>
     <Button
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="读取外部存储文件"
         android:onClick="bt7_onClick"/>

java类：

 //保存资产文件到内部存储
     public void bt4_onClick(View v)
     {
         try {
             //操作assets目录的文件
             //1.得到assetsManager
             AssetManager am = getAssets();
             //2.操作资产目录，边读边写入
             //1)读文件到内存 inputstream
             InputStream is = am.open("yuantu.png");
             //2)写文件到目录 outputstream
             FileOutputStream fos = openFileOutput("test.png",MODE_PRIVATE);
             //先读后写
             byte[] b = new byte[1024];
             int i = 0;
             while ((i = is.read(b))>0)
             {
                 fos.write(b,0,i);
             }
             fos.close();
             is.close();
             Toast.makeText(MainActivity.this, "保存文件成功", Toast.LENGTH_SHORT).show();
         }
         catch (Exception e)
         {
             Toast.makeText(MainActivity.this, "保存文件出错", Toast.LENGTH_SHORT).show();
         }

     }
     //设置图片指向内部存储
     public void bt5_onClick(View v)
     {
         //1.得到文件路径
         String path = getFilesDir().getAbsolutePath()+"/test.png";
         Toast.makeText(MainActivity.this, "path = "+path, Toast.LENGTH_SHORT).show();
         //2.从内部存储的图片得到Bitmap,BitmapFactory.decodeFile("文件路径");
         Bitmap bm = BitmapFactory.decodeFile(path);
         //3.设置图片视图的图片来源
         iv_1.setImageBitmap(bm);
     }
     //写入外部存储文件
     public void bt6_onClick(View v)
     {
         //1.判断SD卡是否挂载
         if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
         {
             //得到文本框内容
             String str = et_1.getText().toString();
             try {
                 //写入
                 //1.构造输出流
                 //1）得到文件路径
                 //得到SD卡根目录
                 String path = Environment.getExternalStorageDirectory().getAbsolutePath();

                 //得到包名对应的目录
 //                String path = getExternalFilesDir("Music").getCanonicalPath();
                 Toast.makeText(MainActivity.this, "path = "+path, Toast.LENGTH_LONG).show();
                 //2）构造
                 FileOutputStream fos = new FileOutputStream(path+"/test.txt");
                 PrintStream ps = new PrintStream(fos);
                 ps.print(str);
                 ps.close();
                 fos.close();
                 Toast.makeText(MainActivity.this, "写入外部文件成功", Toast.LENGTH_SHORT).show();
             }
            catch (Exception e)
            {
                Toast.makeText(MainActivity.this, "存储文件出错", Toast.LENGTH_SHORT).show();
            }
         }
         else
         {
             Toast.makeText(MainActivity.this, "SD卡没有挂载", Toast.LENGTH_SHORT).show();
         }
     }
     //读取外部存储文件
     public void bt7_onClick(View v)
     {
         //1.判断SD卡是否挂载
         if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
         {
             try {
                 String path = getExternalFilesDir("Music").getCanonicalPath()+"/test.txt";
                 FileInputStream fis = new FileInputStream(path);
                 byte[] b = new byte[1024];
                 int i = 0;
                 String str = "";
                 while ((i = fis.read(b))>0)
                 {
                     str += new String(b,0,i);
                 }
                 fis.close();
                 Toast.makeText(MainActivity.this, "文件内容 = "+str, Toast.LENGTH_SHORT).show();
             }
            catch (Exception e)
            {
                Toast.makeText(MainActivity.this, "读取外部文件失败", Toast.LENGTH_SHORT).show();
            }
         }
         else
         {
             Toast.makeText(MainActivity.this, "SD没有挂载", Toast.LENGTH_SHORT).show();
         }
     }