Question

当我尝试运行模拟器时，calculateButton.Click + =委托发生异常，我试图制作一个小费计算器，因此当用户单击按钮时，应用程序便开始计算。

该异常表明抛出System.NullReferenceException对象引用未设置为对象的实例

我尝试了很多事情

Button calculateButton;
protected override void OnCreate(Bundle bundle)
{
   base.OnCreate(bundle);
   SetContentView(Resource.Layout.activity_main);
   calculateButton = FindViewById<Button>(Resource.Id.calculateButton);
   calculateButton.Click += delegate
            {

                "insert calculations"
            };
        }

我也尝试过

Button calculateButton;
protected override void OnCreate(Bundle bundle)
{
   base.OnCreate(bundle);
   SetContentView(Resource.Layout.activity_main);
   calculateButton = FindViewById<Button>(Resource.Id.calculateButton);
   calculateButton.Click += OnCalculateClick;

   void OnCalculateClick (object sender, EventArgs e)
            {

                "insert calculations"
            };
        }

我期望的是，当我单击按钮时，计算将开始

编辑：这是activity_main.axml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:minWidth="25px"
        android:minHeight="25px"
        android:id="@+id/linearLayout1">

    </LinearLayout >

    <include
        layout="@layout/content_main" />
    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

这是content_main.axml，我按教程中的说明在此处添加了按钮

<?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">

    <EditText
        android:imeActionId="@+id/inputBill"
        android:layout_width ="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/editText1"
        android:layout_marginBottom="0.0dp"
        android:layout_marginTop="0.0dp" />

    <Button
        android:imeActionId="@+id/calculateButton"
        android:layout_width ="match_parent"
        android:layout_height="wrap_content"
        android:text         ="CALCULATE"
        android:id="@+id/button1" />


</LinearLayout>

Answer 1

正确用法如下

您的活动中：

Button calculateButton;
protected override void OnCreate(Bundle savedInstanceState)
  {
      base.OnCreate(savedInstanceState);

      // Create your application here
      SetContentView(Resource.Layout.activity_main);
      calculateButton = FindViewById<Button>(Resource.Id.calculateButton);
      calculateButton.Click += delegate
        {

            "insert calculations"
        };
  }

然后在对应 axml（此处为 activity_main ）中：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent">
   <Button
     android:id="@+id/calculateButton"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"   
     android:text="Calculate"
    />
</RelativeLayout>

Xamarin.Android Click Button事件提供了异常，我该如何解决？

1 个答案: