将 ArrayList 保存到 android 上的文件 [英] Save an ArrayList to File on android
问题描述
我有一个充满字符串的 ArrayList，用户填充它以在 ListView 中的不同活动中使用以查看他们保存的字符串.我希望他们填充的 ArrayList 被保存，但我对如何让它工作感到非常迷茫.我试过 FileOutputStream、SharedPreferences.我看了很多例子.
I have an ArrayList full of strings that the user populated it with to use in a different activity in a ListView to view the strings they have saved. I want the ArrayList they populated to be saved but I am so lost on how to get it to work. I've tried FileOutputStream, SharedPreferences. I looked at many examples.
例如我有
ArrayList<String> give = new ArrayList<String>();
并保存我尝试过的数组列表
and to save the arraylist ive tried stuff like
FileOutputStream fos = openFileOutput(MYFILENAME, Context.MODE_PRIVATE);
fos.write(give.getBytes());
fos.close();
但这根本不起作用
推荐答案
这里有一些代码来获取可序列化的对象并将其写入文件，这可能是您需要的.使用 ArrayList 对其进行了测试，效果很好.您还可以修改输出，而不是将其写入文件，您可以使用 extras 或其包将其传递给活动.我将这种方法用于 android 版本 <3.0.
Here is some code to take a serializable object and write it to file, this maybe what you need. Tested it out with and ArrayList and it works fine. You can also modify the output and instead of writing it to file you can pass it to an activity using extras or its bundle. I used this method for android versions < 3.0.
读取已经包含序列化对象的文件:
To Read a file already containing serialized object:
String ser = SerializeObject.ReadSettings(act, "myobject.dat");
if (ser != null && !ser.equalsIgnoreCase("")) {
Object obj = SerializeObject.stringToObject(ser);
// Then cast it to your object and
if (obj instanceof ArrayList) {
// Do something
give = (ArrayList<String>)obj;
}
}
将对象写入文件使用:
String ser = SerializeObject.objectToString(give);
if (ser != null && !ser.equalsIgnoreCase("")) {
SerializeObject.WriteSettings(act, ser, "myobject.dat");
} else {
SerializeObject.WriteSettings(act, "", "myobject.dat");
}
序列化对象的类:
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStreamWriter;
import java.io.Serializable;
import android.content.Context;
import android.util.Base64InputStream;
import android.util.Base64OutputStream;
import android.util.Log;
/**
* Take an object and serialize and then save it to preferences
* @author John Matthews
*
*/
public class SerializeObject {
private final static String TAG = "SerializeObject";
/**
* Create a String from the Object using Base64 encoding
* @param object - any Object that is Serializable
* @return - Base64 encoded string.
*/
public static String objectToString(Serializable object) {
ByteArrayOutputStream out = new ByteArrayOutputStream();
try {
new ObjectOutputStream(out).writeObject(object);
byte[] data = out.toByteArray();
out.close();
out = new ByteArrayOutputStream();
Base64OutputStream b64 = new Base64OutputStream(out,0);
b64.write(data);
b64.close();
out.close();
return new String(out.toByteArray());
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
/**
* Creates a generic object that needs to be cast to its proper object
* from a Base64 ecoded string.
*
* @param encodedObject
* @return
*/
public static Object stringToObject(String encodedObject) {
try {
return new ObjectInputStream(new Base64InputStream(
new ByteArrayInputStream(encodedObject.getBytes()), 0)).readObject();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* Save serialized settings to a file
* @param context
* @param data
*/
public static void WriteSettings(Context context, String data, String filename){
FileOutputStream fOut = null;
OutputStreamWriter osw = null;
try{
fOut = context.openFileOutput(filename, Context.MODE_PRIVATE);
osw = new OutputStreamWriter(fOut);
osw.write(data);
osw.flush();
//Toast.makeText(context, "Settings saved",Toast.LENGTH_SHORT).show();
} catch (Exception e) {
e.printStackTrace();
// Toast.makeText(context, "Settings not saved",Toast.LENGTH_SHORT).show();
}
finally {
try {
if(osw!=null)
osw.close();
if (fOut != null)
fOut.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* Read data from file and put it into a string
* @param context
* @param filename - fully qualified string name
* @return
*/
public static String ReadSettings(Context context, String filename){
StringBuffer dataBuffer = new StringBuffer();
try{
// open the file for reading
InputStream instream = context.openFileInput(filename);
// if file the available for reading
if (instream != null) {
// prepare the file for reading
InputStreamReader inputreader = new InputStreamReader(instream);
BufferedReader buffreader = new BufferedReader(inputreader);
String newLine;
// read every line of the file into the line-variable, on line at the time
while (( newLine = buffreader.readLine()) != null) {
// do something with the settings from the file
dataBuffer.append(newLine);
}
// close the file again
instream.close();
}
} catch (java.io.FileNotFoundException f) {
// do something if the myfilename.txt does not exits
Log.e(TAG, "FileNot Found in ReadSettings filename = " + filename);
try {
context.openFileOutput(filename, Context.MODE_PRIVATE);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
} catch (IOException e) {
Log.e(TAG, "IO Error in ReadSettings filename = " + filename);
}
return dataBuffer.toString();
}
}
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