如何从android 5中的外部存储中删除文件

File f=new File(MyPath);
f.delete();

我使用了权限WRITE_EXTERNAL_STORAGE和READ_EXTERNAL_STORAGE,但它在Android 5中不起作用.

Logcat消息：

java.io.FileNotFoundException: storage/external_SD/mm.txt: open Failed: EACCES (Permission denied)

清单文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="@R_262_10107@://scheR_67_11845@as.android.com/apk/res/android"
    package="com.example.mahestan_progrAMMing.myapplication">

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <application
        android:allowBACkup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@String/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>