Parcelable writeToParcel(): What's the best way to write multiple variables of the same type?

Question

I have ten strings: str1, str2, str3...,str10 (not actual string names). Do I have to do dest.writeString(str_n) for all 10 strings or is there an easier way to do this? How would I read them back in?

Example:

@Override
public void writeToParcel(Parcel dest, int flags) {
      dest.writeString(str1);       
      dest.writeString(str2);   
      dest.writeString(str3);   
      dest.writeString(str4);   
      dest.writeString(str5);   
      dest.writeString(str6);   
      dest.writeString(str7);   
      dest.writeString(str8);   
      dest.writeString(str9);
      dest.writeString(str10);      
}

As you can see, this could become very lengthy. Any suggestions would help! Thanks!

writeStringArray? did you try this? – pskink Jun 23 '14 at 19:00 — pskink, Jun 23 '14 at 19:00
how would i read them back into each variable? – kyrax Jun 23 '14 at 22:06 — kyrax, Jun 23 '14 at 22:06
just read Parcel.readString* documentation – pskink Jun 24 '14 at 06:30 — pskink, Jun 24 '14 at 06:30

score 15 · Accepted Answer · edited Oct 29 '15 at 08:29

If you have 10 strings in your Parcelable class and you want to restore their values, then that's the way to do it. You read them back in by creating a Parcelable.Creator and a private constructor that accepts a Parcel object as its parameter, then in that constructor you call readString() on the Parcel in the same order you called writeString(). See http://developer.android.com/reference/android/os/Parcelable.html

It would look something like this:

public class MyParcelable implements Parcelable {

     private String str1;
     private String str2;
     private String str3;
     private String str4;
     private String str5;
     private String str6;
     private String str7;
     private String str8;
     private String str9;
     private String str10;

     public int describeContents() {
         return 0;
     }

     public void writeToParcel(Parcel dest, int flags) {
      dest.writeString(str1);       
      dest.writeString(str2);   
      dest.writeString(str3);   
      dest.writeString(str4);   
      dest.writeString(str5);   
      dest.writeString(str6);   
      dest.writeString(str7);   
      dest.writeString(str8);   
      dest.writeString(str9);
      dest.writeString(str10);
     }

     public static final Parcelable.Creator<MyParcelable> CREATOR
             = new Parcelable.Creator<MyParcelable>() {
         public MyParcelable createFromParcel(Parcel in) {
             return new MyParcelable(in);
         }

         public MyParcelable[] newArray(int size) {
             return new MyParcelable[size];
         }
     };

     private MyParcelable(Parcel in) {
         str1 = in.readString();       
         str2 = in.readString();       
         str3 = in.readString();       
         str4 = in.readString();       
         str5 = in.readString();       
         str6 = in.readString();       
         str7 = in.readString();       
         str8 = in.readString();       
         str9 = in.readString();       
         str10 = in.readString();       
     }
 }

Thank you for **in the same order you called `writeString()`** — Bugs Happen, Oct 29 '15 at 07:58
Yea the best answer to this question would look like this: __**read values in the same order you wrote it into parcelable**__ :) — Srneczek, Nov 12 '15 at 18:35

score 1 · Answer 2 · answered Jun 23 '14 at 23:17

For writing them, you could do the shortcut as suggested to write a string array. Reading them back in, however, you're still going to have to assign them back one by one.

You could write a couple of utility methods:

public static void writeStrings(Parcel out, String... strings) {
    out.writeInt(strings.length);
    for (String string : strings) {
        out.writeString(string);
    }
}

public static String[] readStrings(Parcel in) {
    final String[] strings = new String[in.readInt()];
    for (int i = 0; i < strings.length; i++) {
        strings[i] = in.readString();
    }
    return strings;
}

and then to write them:

writeStrings(dest, str1, str2, str3, str4, str5);

and to read them:

String[] strings = readStrings(dest);
str1 = strings[0];
str2 = strings[1];
str3 = strings[2];
str4 = strings[3];
str5 = strings[4];

Honestly, just for maintainability and readability, I'd suggest avoiding doing anything too clever here and just write them out one by one. Parcelable is a nice mechanism; unfortunately, there's just not much you can do to reduce the boilerplate for cases like this.

Parcelable writeToParcel(): What's the best way to write multiple variables of the same type?

2 Answers2