Android SDK - 無法讀/寫文件

Question

我對Android SDK非常陌生，無法讀寫文件。請注意，我對Java也很陌生。該程序應該簡單地將一個字符串寫入一個文件，讀取相同的字符串，然後將TextView更改爲該讀取的字符串。程序運行但不改變TextView。有人可以告訴我我做錯了什麼嗎？謝謝。

MainActivity.java

package com.example.test; 

import java.io.BufferedReader; 
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.FileReader; 

import android.app.Activity; 
import android.content.Context; 
import android.os.Bundle; 
import android.view.Menu; 
import android.widget.TextView; 

public class MainActivity extends Activity { 

    public String readFileLine(String filepath) throws java.io.FileNotFoundException, java.io.IOException { 
     //opens file and returns first line 
     FileReader fr = new FileReader (new File(filepath)); 
     BufferedReader inputStream = new BufferedReader (fr); 
     String temp = inputStream.readLine(); 
     inputStream.close(); 
     return temp; 
    } 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     FileOutputStream outputStream_local; 
     try { 
      outputStream_local = openFileOutput("local.txt", Context.MODE_PRIVATE); 
      outputStream_local.write("asdf".getBytes()); 
      outputStream_local.close(); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
     TextView temp = (TextView) findViewById(R.id.getMe); 

     try { 
      temp.setText(readFileLine(getFilesDir().toString() + "local.txt")); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

} 

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    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=".MainActivity" > 

    <TextView 
     android:id="@+id/getMe" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="@string/hello_world" /> 

</RelativeLayout> 

logcat的輸出

[2014-02-08 11:18:11 - Test] ------------------------------ 
[2014-02-08 11:18:11 - Test] Android Launch! 
[2014-02-08 11:18:11 - Test] adb is running normally. 
[2014-02-08 11:18:11 - Test] Performing com.example.test.MainActivity activity launch 
[2014-02-08 11:18:11 - Test] Automatic Target Mode: Unable to detect device compatibility. Please select a target device. 
[2014-02-08 11:18:14 - Test] Uploading Test.apk onto device '014FD8210301B01A' 
[2014-02-08 11:18:14 - Test] Installing Test.apk... 
[2014-02-08 11:18:18 - Test] Success! 
[2014-02-08 11:18:18 - Test] Starting activity com.example.test.MainActivity on device 014FD8210301B01A 
[2014-02-08 11:18:18 - Test] ActivityManager: Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=com.example.test/.MainActivity } 
[2014-02-08 11:18:38 - Test] ------------------------------ 
[2014-02-08 11:18:38 - Test] Android Launch! 
[2014-02-08 11:18:38 - Test] adb is running normally. 
[2014-02-08 11:18:38 - Test] Performing com.example.test.MainActivity activity launch 
[2014-02-08 11:18:38 - Test] Automatic Target Mode: Unable to detect device compatibility. Please select a target device. 
[2014-02-08 11:18:41 - Test] Application already deployed. No need to reinstall. 
[2014-02-08 11:18:41 - Test] Starting activity com.example.test.MainActivity on device 014FD8210301B01A 
[2014-02-08 11:18:41 - Test] ActivityManager: Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=com.example.test/.MainActivity } 
[2014-02-08 11:18:41 - Test] ActivityManager: Warning: Activity not started, its current task has been brought to the front 

Answer 1

確保您有給下面的manifest.xml文件

權限到您的應用

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

您需要授予這些權限以寫入文件並從設備讀取文件。