Xamarin FindViewById返回null [英] Xamarin FindViewById returns null

问题描述

大家好，我需要一点点的建议。我试图用Xamarin让C＃做一个Android应用程序。我做了两个布局，并在他们每个人我做牵引按钮them.I之间进行导航试过这样的：

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.I tried like this:

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;
            this.FindViewById<Button>(Resource.Id.BackButton).Click += this.Back;
        }

        public void Forward(object sender, EventArgs e)
        {
            this.SetContentView(Resource.Layout.Main2);
        }

        public void Back(object sender, EventArgs e)
        {
            this.SetContentView(Resource.Layout.Main);
        }
    }
}

但每次当我启动应用程序，我得到这个errror时间信息：System.NullReferenceException已经thrown.Object引用不设置到对象的实例。任何意见或更好的主意吗？

But every time when I start the app I get this errror: System.NullReferenceException has been thrown.Object reference not set to an instance of an object. Any advice or better idea?

推荐答案

正在设置主为您的活动的布局，然后在$ C $以下行c您是要求找到一个名为返回在运行时是不是这个布局的组成部分按钮。这意味着下面一行将返回null：

You are setting Main as the layout for your activity and then in the following lines of code you are asking to find a button named Back at runtime which is not part of this layout. This means the following line will return null:

FindViewById<Button>(Resource.Id.BackButton)

现在如果你这样做 FindViewById＆LT;按钮＆GT;（Resource.Id.BackButton）。点击，你一定会得到一个 System.NullReferenceException 。

Now if you do FindViewById<Button>(Resource.Id.BackButton).Click, you will definitely get a System.NullReferenceException.

编辑：

在视图中的意见，这里是你应该做的，达到你在找什么：

In view of the comments, here is what you should do to achieve what you are looking for:

创建两个不同的活动（ MAIN1 和 MAIN2 ）。在 MAIN1 你做的：

Create two different activities (Main1 and Main2). In Main1 you do:

    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.StartActivity (typeof(Main2));
    }

然后在 MAIN2 ，你做的：

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        this.SetContentView(Resource.Layout.Main2);

        this.FindViewById<Button>(Resource.Id.BackButton).Click += this.Back;
    }

    public void Back(object sender, EventArgs e)
    {
        this.StartActivity (typeof(Main));
    }

这篇关于Xamarin FindViewById返回null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！