android 6.0 open failed enoent (no such file or directory)

偶然在看網友們在Google Play Store 裡的留言，發現有人說會crash, 他用的 Android 是 6.0 版，窮到爆的我，怎麼可能有錢去買設備來測，還好前陣子下載了 Genymotion，正好解決 Android 6.0 遇到的問題。

實際 debug 後看到的錯誤訊息是：

java.io.IOException: open failed: ENOENT (No such file or directory)

在 AndroidManifest.xml 也有宣告權限：

<uses-permission android:name=”android.permission.WRITE_EXTERNAL_STORAGE” />

寫入檔案前，也有先create dirs：

final File dir = new File(root_path);
dir.mkdirs(); //create folders where write files

試到這裡，這樣還是不行。

建立檔案先，取出權限看看：

int permissionCheck = ContextCompat.checkSelfPermission(getActivity(),
Manifest.permission.WRITE_EXTERNAL_STORAGE);

permissionCheck 結果是 true, 有權限，為什麼還是不能寫入 @_@;

最後解法是用這一段 code，新的 Android 存取外部共用空間時，不能偷偷摸摸存取，要設備主人的同意。

public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/* Request user permissions in runtime */
ActivityCompat.requestPermissions(MainActivity.this,
new String[] {
Manifest.permission.READ_EXTERNAL_STORAGE,
Manifest.permission.WRITE_EXTERNAL_STORAGE
},
100);
/* Request user permissions in runtime */
String storagePath = Environment.getExternalStorageDirectory().getAbsolutePath();
String rootPath = storagePath + "/test";
String fileName = "/test.zip";
File root = new File(rootPath);
if(!root.mkdirs()) {
Log.i("Test", "This path is already exist: " + root.getAbsolutePath());
}
File file = new File(rootPath + fileName);
try {
int permissionCheck = ContextCompat.checkSelfPermission(MainActivity.this, android.Manifest.permission.WRITE_EXTERNAL_STORAGE);
if (permissionCheck == PackageManager.PERMISSION_GRANTED) {
if (!file.createNewFile()) {
Log.i("Test", "This file is already exist: " + file.getAbsolutePath());
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
@TargetApi(23)
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
switch (requestCode) {
case 100:
if (grantResults.length > 0
|| grantResults[0] == PackageManager.PERMISSION_GRANTED
|| grantResults[1] == PackageManager.PERMISSION_GRANTED) {
/* User checks permission. */
} else {
Toast.makeText(MainActivity.this, "Permission is denied.", Toast.LENGTH_SHORT).show();
finish();
}
return;
}
}
}

另一個解法是盡量不要去存取共用空間，改用 getExternalCacheDir()。

public static void storeSnapshot(List<WifiReading> readings, String fileName, Context c) {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
// We can read and write the external storage
try {
JSONArray json = readingsToJson(readings);
File root = c.getExternalCacheDir();
File jsonFile = new File(root, constructFileName(fileName));
FileOutputStream out;
out = new FileOutputStream(jsonFile);
out.write(json.toString().getBytes());
out.close();
U.showToast(constructFileName(fileName));
Log.d(TAG, "Successfully stored snapshot to SDCard");
} catch (Exception e) {
U.showToast("Could not save the snapshot on the SDCard.");
Log.e(TAG, "Could not save the snapshot on the SDCard.", e);
}
} else {
U.showToast("Cannot write to external storage.");
}
}

相關文章：

Requesting Permissions at Run Time

https://developer.android.com/training/permissions/requesting.html

Beginning in Android 6.0 (API level 23), users grant permissions to apps while the app is running, not when they install the app.