使用 getFilesDir() 时应用程序上下文返回 null

我不知道为什么会发生这种情况。当我检查 DDMS 时也没有文件目录。我正在尝试在我的应用程序子类中访问此文件夹。知道为什么会发生这种情况吗？ 我需要应用程序上下文是全局的，这样我就可以在不扩展 Activity 的类上使用。

package mci.multipratic;

import java.io.File;
import java.io.FileInputStream;
import java.util.Properties;
import android.app.Application;
import android.content.Context;

public class MultiPraticApp extends Application
{   
private static MultiPraticApp instance;
public static MultiPraticAppHelper helper;

public MultiPraticApp()
{       
    instance = MultiPraticApp.this;
    helper = new MultiPraticAppHelper();
}   

public static Context getContext()
{       
    return instance;
}
}

class MultiPraticAppHelper
{
private int offsets = 0;
private int productIndex = 0;
private int recipeId = 0;
private Recipe selectedRecipe;  
private Properties configFile;

public MultiPraticAppHelper()
{
    Context context = MultiPraticApp.getContext();                      

    String path = context.getFilesDir() + "/config.properties";

    File file = new File(path);

    try
    {
        FileInputStream fis = new FileInputStream(file);

        Properties properties = new Properties();
        properties.load(fis);

        fis.close();
    }catch(Exception ex)
    {
        ex.printStackTrace();
    }
}

我的清单文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="mci.multipratic"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk android:minSdkVersion="4" />  

<application android:name=".MultiPraticApp"        
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name">
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name" 
        android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />                
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity
        android:name=".EnableProductsActivity"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen">          
    </activity>

    <activity
        android:name=".RecipeSelectionActivity"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen">           
    </activity>

    <activity
        android:name=".ProductAdjustsActivity"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen"
        >
    </activity>               
</application>  

我相信问题是您正在尝试在构造函数中进行初始化。将构造函数中的代码移至 Application 类的 OnCreate 中。

@Override
public void onCreate() {
  super.onCreate();
  if(instance != null)
     instance = MultiPraticApp.this;
  if(helper != null)
     helper = new MultiPraticAppHelper();

}