Question

我还在和Xamarin一起训练。现在我遇到的问题是我无法将对象设置为资源而且我收到此错误：引用未设置为对象的实例。

我做了什么，我创建了Activity类。在那里我创建了LinearLayout对象。想法是当我点击蓝色区域对象然后滑动到另一个页面：车辆没有停放布局。但它不起作用，我收到错误。这是我的ZonesActivity类：

namespace CustomActionBarParking
    {
        [Activity(Label = "@+id/blueZoneLayout")]

        public class ZonesActivity : Activity
        LinearLayout mBlueZone;
        protected override void OnCreate(Bundle bundle)
            {
                base.OnCreate(bundle);
                mBlueZone = FindViewById<LinearLayout>(Resource.Id.blueZoneLayout);
                if (mBlueZone != null)
                {
                    mBlueZone.Click += (object sender, EventArgs args) =>
                    {
                        SetContentView(Resource.Layout.vehicle_not_parked);
                    };
                }
                else
                {
                    throw new ArgumentException("Parameter cannot be null", "");
                }
}}}

这是我对zones_list.axml文件的一部分：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:weightSum="100">
<LinearLayout
        android:orientation="horizontal"
        android:layout_weight="11"
        android:minWidth="25px"
        android:minHeight="25px"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/blueZoneLayout"
        android:weightSum="100"
        android:focusableInTouchMode="true"
        android:background="@android:color/background_light">
        <TextView
            android:text="M"
            android:layout_weight="10"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:id="@+id/textView2"
            android:textColor="@android:color/holo_blue_dark"
            android:gravity="center" />
        <TextView
            android:text="Blue zone"
            android:layout_weight="80"
            android:textAppearance="?android:attr/textAppearanceLarge"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:id="@+id/textView3"
            android:textColor="@android:color/holo_blue_dark"
            android:gravity="center" />
        <TextView
            android:text="i"
            android:layout_weight="10"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:id="@+id/textView4"
            android:textColor="@android:color/holo_blue_dark"
            android:gravity="center" />
</LinearLayout>

为什么我无法设置对象的引用？而且我想提一下，我正在从MainActivity.cs调用zones_list布局。编辑：抛出新的ArgumentException我得到了这个：

Unhandled Exception:
System.ArgumentException: Parameter cannot be null

Answer 1

mBlueZone = FindViewById<LinearLayout>(Resource.Id.blueZoneLayout);

在这种情况下，变量mBlueZone将始终为null。 FindViewById在布局中查找View Id blueZoneLayout，Activity已设置为SetContentView(Resource.Layout.zones_list);的ContentView。您需要在从中渗透视图之前设置ContentView。你应该添加这一行

mBlueZone = FindViewById<LinearLayout>(Resource.Id.blueZoneLayout);

之前

Activity

编辑：以上部分将解决问题（根据您的逻辑）和工作。但这不是推荐的做法。您应该为Vehicle not Parked Layout单独public class LaunchActivity:Activity { protected override void OnCreate (Bundle bundle) { base.OnCreate (bundle); SetContentView(Resource.Layout.zones_list); mBlueZone = FindViewById<LinearLayout>(Resource.Id.blueZoneLayout); mBlueZone.Click += (object sender, EventArgs args) => { StartActivity(typeof(NotParkedActivity)); }; } } public class NotParkedActivity :Activity { protected override void OnCreate (Bundle bundle) { base.OnCreate (bundle); SetContentView(Resource.Layout. vehicle_not_parked); } }。

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Xamarin System.ArgumentException：参数不能为null

1 个答案: