Using PutParcelable with Bundle from OnSaveInstanceState & OnCreate

Question

I have several Views for which I want to save the state using the PutParcelable method of the Bundle passed to OnSaveInstanceState & OnCreate. I am very new to Xamarin.Android, and have never used PutParcelable before. Can anybody tell me how to do the create the IParcelable from a View (the Views I am using are not custom, they are standard Views, so I think they have IParcelable implemented), as well as recreate the View afterwards using the IParcelable? Thanks.

Answer

Hello,

Welcome to our Microsoft Q&A platform!

I made a simple demo based on the official sample activitylifecycle, and it works properly.

You can refer to the following code :

1.create a class Book and implement Java.Lang.Object, IParcelable

public class Book: Java.Lang.Object, IParcelable  
{  
    public string Name;  
 public string Author;  
 public string Editor;  
 public int Year;  
 public string CoverPath;  

 public override string ToString ()  
 {  
 return string.Format ("{0} - {1}", Name, Author);  
 }  

 [ExportField ("CREATOR")] // Need a reference to Mono.Android.Export  
 public static BookCreator InitializeCreator ()  
 {  
 return new BookCreator ();  
 }  

 public void WriteToParcel (Parcel dest, ParcelableWriteFlags flags)  
 {  
 dest.WriteString (Name);  
 dest.WriteString (Author);  
 dest.WriteString (Editor);  
 dest.WriteInt (Year);  
 dest.WriteString (CoverPath);  
 }  

 public int DescribeContents ()  
 {  
 return 0;  
 }  
}  

 public class BookCreator : Java.Lang.Object, IParcelableCreator  
 {  
 public Java.Lang.Object CreateFromParcel(Parcel source)  
 {  
 Book book = new Book();  
 book.Name = source.ReadString();  
 book.Author = source.ReadString();  
 book.Editor = source.ReadString();  
 book.Year = source.ReadInt();  
 book.CoverPath = source.ReadString();  
 return book;  
 }  

 public Java.Lang.Object[] NewArray(int size)  
 {  
 return new Java.Lang.Object[size];  
 }  
}

2.in MainActivity, we just added the following code in OnCreate and OnSaveInstanceState:

    protected override void OnSaveInstanceState (Bundle outState)  
    {  
        Book book = new Book {Name="book1", Author ="Hello", Editor= "Editor1", Year=2020 };  
        outState.PutParcelable("mBook",book);  

        Log.Debug(GetType().FullName, "Activity A - Saving instance state");  

        // always call the base implementation!  
        base.OnSaveInstanceState (outState);      
    }

3.method OnCreate:

    protected override void OnCreate(Bundle bundle)  
    {  
       Log.Debug(GetType().FullName, "Activity A - OnCreate");  
      base.OnCreate(bundle);  
      SetContentView (Resource.Layout.Main);  

        if (bundle != null)  
        {  
            Book book = (Book)bundle.GetParcelable("mBook");  

            Log.Debug(GetType().FullName, "Activity A - Recovered instance state");  
            Toast.MakeText(this,"book name: " + book.Name + " , book Author : " + book.Author, ToastLength.Short).Show();  
        }

And when we rotate the device to landscape mode, the book data is preserved!

Best Regards,

Jessie Zhang

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Using PutParcelable with Bundle from OnSaveInstanceState & OnCreate

1 answer