####获取外置内存的大小####

public class MainActivity extends Activity {

@SuppressWarnings("deprecation")
    @Override
    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){
            //android的版本高于4.3
             blockSize = stat.getBlockSizeLong();
             totalBlocks = stat.getBlockCountLong();
             availableBlocks = stat.getAvailableBlocksLong();
        }
        else{
            blockSize = stat.getBlockSize();
            totalBlocks = stat.getBlockCount();
            availableBlocks = stat.getAvailableBlocks();
        }
        
        //获取到输入框的id值
        TextView tv = (TextView) findViewById(R.id.tv);
        tv.setText(formatSize(availableBlocks * blockSize));
    }

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

}