公共外部存储

Question

我尝试将文件txt保存到公共外部存储

文件清单

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.hikilam.publicprivateexternalstorage">

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

</manifest>

file xml

<RelativeLayout
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.hikilam.publicprivateexternalstorage.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Username"
        android:id="@+id/textView"
        android:layout_marginTop="126dp"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/user"
        android:width="200dp"
        android:layout_alignBottom="@+id/textView"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Public"
        android:id="@+id/button"
        android:onClick="publicStorage"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true" />
</RelativeLayout>

保存功能：

  public void publicStorage(View view) {
        String data = username.getText().toString();
        File file = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
        File file1 = new File(file, "file.txt");
        FileOutputStream fileOutputStream=null;
        try {
            fileOutputStream=new FileOutputStream(file1);
            fileOutputStream.write(data.getBytes());
            Toast.makeText(this,"Stored Succeful"+file1.getAbsolutePath(),Toast.LENGTH_LONG).show();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                fileOutputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

错误代码

02-29 20:53:19.511 4696-4696/? E/AndroidRuntime: FATAL EXCEPTION: main
                                             Process: com.example.hikilam.publicprivateexternalstorage, PID: 4696
                                             java.lang.IllegalStateException: Could not execute method for android:onClick