Android檢查SD卡是否可讀寫

因為external storage可能是不可用的，比如遇到SD卡被拔出等情況時。因此在訪問之前應對其可用性進行檢查。我們可以通過執 行 getExternalStorageState()來查詢external storage的狀態。若返回狀態為MEDIA_MOUNTED, 則 可以讀寫。

/ Checks if external storage is available for read and write /
public boolean isExternalStorageWritable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        return true;
    }
    return false;
}

/ Checks if external storage is available to at least read /
public boolean isExternalStorageReadable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state) ||
        Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        return true;
    }
    return false;
}</pre>