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();
        }
    }