Error: java.lang.NoSuchMethodException

Question

Hi guys I need a little advice. I trying to made an android app using Xamarin so C#. I made two layouts and in each one of them I made tow buttons to navigate between them. The first button works but the other don't. I bring the error java.lang.NoSuchMethodException.

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace SOLVER
{
    [Activity (Label = "SOLVER", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
{
    private void BUTONULback (View v)
    {
        Button ButonulBack = FindViewById<Button> (Resource.Id.Butonulback);
        ButonulBack.Click += delegate { SetContentView (Resource.Layout.Main); };
    }

    protected override void OnCreate (Bundle bundle)
    {
        base.OnCreate (bundle);
        SetContentView (Resource.Layout.Main);

        Button button = FindViewById<Button> (Resource.Id.butonulSolve);
        button.Click += delegate { SetContentView (Resource.Layout.Main2); };


    }
}

}

At the other layout I use the behavior OnClick with the tag BUTTONback.I tried to move the paragraph

Button ButonulBack = FindViewById<Button> (Resource.Id.Butonulback);
ButonulBack.Click += delegate { SetContentView (Resource.Layout.Main) ;};

down and I bring the error "has been thrown. Object reference not set to an instance of an object".

Thanks!

Could you also provide the layouts please? In the question you're stating you're getting a Java.Lang.NoSuchMethodException. But later on you're stating it's Object reference not set to an instance of an object, which is a NullRererenceException. So which is it? Both? — Frank, Aug 08 '14 at 12:37
I can't answer to you like question because I've got a too low reputation so I write here : http://txs.io/ZHpb — user3836246, Aug 08 '14 at 12:53

Frank · Answer 1 · 2014-08-09T11:25:04.640

You're mixing different ways to hookup buttons and methods.

Option 1 - Programmatically

MainActivity.cs

using System;

using Android.App;
using Android.OS;
using Android.Views;
using Android.Widget;


namespace Example
{
    [Activity(Label = "Example", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            this.SetContentView(Resource.Layout.Main);

            this.FindViewById<Button>(Resource.Id.ForwardButton).Click += this.Forward;
        }

        public void Forward(object sender, EventArgs e)
        {
            this.SetContentView(Resource.Layout.Main2);
            this.FindViewById<Button>(Resource.Id.BackButton).Click += this.Back;
        }

        public void Back(object sender, EventArgs e)
        {
            this.SetContentView(Resource.Layout.Main);
            this.FindViewById<Button>(Resource.Id.ForwardButton).Click += this.Forward;
        }
    }
}

Main.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <Button
        android:id="@+id/ForwardButton"
        android:text="Forward"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

Main2.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView
        android:id="@+id/CheckedTextView"
        android:layout_width="match_parent"
        android:layout_height="326dp"
        android:enabled="false" />
    <Button
        android:id="@+id/BackButton"
        android:text="Back"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

In XML

MainActivity.cs

using System;

using Android.App;
using Android.OS;
using Android.Views;
using Android.Widget;


namespace Example
{
    [Activity(Label = "Example", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            this.SetContentView(Resource.Layout.Main);
        }

        [Java.Interop.Export("OnClick")]
        public void OnClick (View view)
        {
            var button = (Button)view;

            if (button.Id == Resource.Id.ForwardButton) {
                this.SetContentView(Resource.Layout.Main2);
            } else if (button.Id == Resource.Id.BackButton) {
                this.SetContentView(Resource.Layout.Main);
            }
        }
    }
}

Main.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <Button
        android:id="@+id/ForwardButton"
        android:text="Forward"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="OnClick" />
</LinearLayout>

Main2.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView
        android:id="@+id/CheckedTextView"
        android:layout_width="match_parent"
        android:layout_height="326dp"
        android:enabled="false" />
    <Button
        android:id="@+id/BackButton"
        android:text="Back"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="OnClick" />
</LinearLayout>

At first option I bring the error "has been thrown. Object reference not set to an instance of an object" and at second the app crash. Thank you anyway! — user3836246, Aug 08 '14 at 17:33
Here it compiles and works normally. Did you try it in a new, separate project? — Frank, Aug 09 '14 at 06:22
I see you already started a new question. http://stackoverflow.com/questions/25209916/xamarin-findviewbyid-returns-null That's not a nice thing to do. — Frank, Aug 09 '14 at 06:43
Sorry but none of your solutions works.And practically my question of this topic was solved. — user3836246, Aug 09 '14 at 08:14
It's clear from from your other question that instead of choosing between solutions you again choose both options. I clearly wrote that you use "OnClick in the layout" or setting up delegate using ".Click += ...". You made typo's (in http://en.textsave.org/2Ipb you suddenly have OnCLick instead of OnClick)... Typo's in ID's can give such errors. You claim both answers don't work. I doubt tested both, the error comes from a line in only one of them. Finally, yes, I see that the programmatic example contains an error. Which I fixed. That doesn't mean the answer didn't solve your problem. — Frank, Aug 09 '14 at 11:24

Error: java.lang.NoSuchMethodException

1 Answers1

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