android 小知识

Logcat

等级

• verbose：冗余，最低等级
• debug：调试
• info：正常等级的信息
• warn：警告
• error：错误

Android的存储

内部存储空间

• RAM内存：运行内存，相当于电脑的内存
• ROM内存：存储内存，相当于电脑的硬盘

//获得data下的应用文件目录
File file = new File(getFilesDir(), "info.txt");
//获得data下的应用缓存目录
File file = new File(getCacheDir(), "info.txt");

外部存储空间

SD卡：相当于电脑的移动硬盘

得到sd目录代码

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
   File path = Environment.getExternalStorageDirectory();
   File file = new File(path+"/info.txt");
}

• 2.2之前，sd卡路径：sdcard
• 4.3之前，sd卡路径：mnt/sdcard
• 4.3开始，sd卡路径：storage/sdcard

得到sd应用目录

//缓存目录
File file = new File(getExternalCacheDir(), "info.txt");
//文件目录
File file = new File(getExternalFilesDir(), "info.txt");

sd总大小和可用量的计算

• 所有存储设备，都会被划分成若干个区块，每个区块有固定的大小
• 存储设备的总大小 = 区块大小 * 区块数量

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        File path = Environment.getExternalStorageDirectory();
        StatFs stat = new StatFs(path.getPath());
        long blockSize;
        long totalBlocks;
        long availableBlocks;
        
        //获取当前系统版本的等级
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2){
             blockSize = stat.getBlockSizeLong();
             totalBlocks = stat.getBlockCountLong();
             availableBlocks = stat.getAvailableBlocksLong();
        }
        else{
            blockSize = stat.getBlockSize();
            totalBlocks = stat.getBlockCount();
            availableBlocks = stat.getAvailableBlocks();
        }
        
        TextView tv = (TextView) findViewById(R.id.tv);
        tv.setText(formatSize(availableBlocks * blockSize));
    }

    private String formatSize(long size) {
        return Formatter.formatFileSize(this, size);
    }