阅读和写作从SD卡上的文件 [英] Reading and Writing a file from SD card

问题描述

我已经买了一本书（开始的Andr​​oid游戏）由Mario Zechner。在149页，他谈到保存和打开的外部存储的文件。据我所知，code，但我不明白为什么它说的：

I have bought a book ("Beginning Android Games") by Mario Zechner. On page 149, he talks about saving and opening a file on External Storage. I understand the code, however I dont understand WHY it says this:

为什么会这样说？我把所有的权限在我的清单：

Why does it say this? I have all the permissions in my Manifest:

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

<application
    android:label="Android Reference"
    android:icon="@drawable/ic_launcher"
    android:debuggable="true">
    <activity
        android:label="Android Reference"
        android:name=".AndroidReferenceActivity" 
        android:screenOrientation="portrait"
        android:configChanges="keyboard|keyboardHidden|orientation">
        <intent-filter >
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity 
        android:label="LifeCycleTest"
        android:name=".LifeCycleTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
    <activity 
        android:label="SingleTouchTest"
        android:name=".SingleTouchTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
    <activity 
        android:label="MultiTouchTest"
        android:name=".MultiTouchTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
    <activity 
        android:label="KeyTest"
        android:name=".KeyTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
     <activity 
        android:label="AccelerometerTest"
        android:name=".AccelerometerTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
     <activity 
        android:label="AssetsTest"
        android:name=".AssetsTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
     <activity 
        android:label="ExternalStorageTest"
        android:name=".ExternalStorageTest"
        android:configChanges="keyboard|keyboardHidden|orientation"/>
</application>
<uses-sdk android:minSdkVersion="8"  android:targetSdkVersion="10"/>
<uses-permission android:name="android.permisson.WRITE_EXTERNAL_STORAGE" android:required="true"/>
<uses-permission android:name="android.permission.WAKE_LOCK" android:required="false"/>

和我的code：

package com.amzoft.android.reference;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.widget.TextView;

public class ExternalStorageTest extends Activity{

@Override
public void onCreate(Bundle saveInstanceState)
{
    super.onCreate(saveInstanceState);
    TextView textView = new TextView(this);
    setContentView(textView);

    String state = Environment.getExternalStorageState();
    if(!state.equals(Environment.MEDIA_MOUNTED))
    {
        textView.setText("SD card is not mounted");
    }else{
        File externalDir = Environment.getExternalStorageDirectory();
        File textFile = new File(externalDir.getAbsolutePath() + File.separator + "text.txt");

        try{
            writeTextFile(textFile, "This is a test >:0\nLINE BREAK");
            String text = readTextFile(textFile);
            textView.setText(text);
            if(!textFile.delete())
            {
                textView.setText("Couldn't remove temporary directory,     sorry mate.");
            }
        }catch(Exception e){
            textView.setText(e.getMessage());
        }
    }   
}

private void writeTextFile(File file, String text) throws IOException
{
    BufferedWriter writer = new BufferedWriter(new FileWriter(file));
    writer.write(text);
    writer.close();
}

private String readTextFile(File file) throws IOException
{
    BufferedReader reader = new BufferedReader(new FileReader(file));
    StringBuilder text = new StringBuilder();
    String line;
    while((line = reader.readLine()) != null)
    {
        text.append(line);
        text.append("\n");//BECAUSE ITS A LINE :D
    }
    reader.close();
    return text.toString();
}

}

我希望有人能帮助我，因为林困惑现在。

I hope someone can help me, because Im confused right now.

推荐答案

我想它的权限问题，加上这两个以清单文件

i think its permissions issue add both of these to Manifest file

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

让我知道它是如何变成了

let me know how it turns out

这篇关于阅读和写作从SD卡上的文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！