android - 使用操作栏时应用程序崩溃，这是怎么回事？

Question

所以我正在学习制作 Android 应用程序的基础知识，现在我正在尝试操作栏。它没有给出任何错误，但是当我在手机上运行该应用程序时，它崩溃了。这是操作栏:

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
<!-- Search, should appear as action button -->
<item android:id="@+id/action_search"
      android:icon="@drawable/ic_action_settings"
      android:title="@string/action_settings"
      android:showAsAction="ifRoom" />
<!-- Settings, should always be in the overflow -->
<item android:id="@+id/action_settings"
      android:title="@string/action_settings"
      android:icon="@drawable/ic_action_search"
      android:showAsAction="always" />          

和主要 Activity java:

    @Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle presses on the action bar items
    switch (item.getItemId()) {
        case R.id.action_search:
        startActivity(new Intent(this, Hallo.class));
            return true;
        case R.id.action_settings:
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }

这是 Hallo.class

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:text="@string/hallo" />

和hallo.java:

package com.example.myfirstapp;

public class Hallo extends MainActivity{
protected void onCreate() {
    setContentView(R.layout.hallo);
}
}

这就是我所拥有的。怎么了？谢谢你的回答。现在我无论如何都在这里，“这个”的 Intent 是什么？再次感谢。

编辑我认为这是堆栈跟踪

Thread [<1> main] (Suspended (exception ActivityNotFoundException)) 
    <VM does not provide monitor information>   
    Instrumentation.checkStartActivityResult(int, Object) line: 1556    
    Instrumentation.execStartActivity(Context, IBinder, IBinder, Activity, Intent, int, Bundle) line: 1431  
    MainActivity(Activity).startActivityForResult(Intent, int, Bundle) line: 3390   
    MainActivity(Activity).startActivityForResult(Intent, int) line: 3351   
    MainActivity(Activity).startActivity(Intent, Bundle) line: 3561 
    MainActivity(Activity).startActivity(Intent) line: 3529 
    MainActivity.onOptionsItemSelected(MenuItem) line: 35   
    MainActivity(Activity).onMenuItemSelected(int, MenuItem) line: 2573 
    PhoneWindow.onMenuItemSelected(MenuBuilder, MenuItem) line: 1059    
    MenuBuilder.dispatchMenuItemSelected(MenuBuilder, MenuItem) line: 735   
    MenuItemImpl.invoke() line: 149 
    MenuBuilder.performItemAction(MenuItem, int) line: 874  
    ActionMenuView.invokeItem(MenuItemImpl) line: 603   
    ActionMenuItemView.onClick(View) line: 148  
    ActionMenuItemView(View).performClick() line: 4162  
    View$PerformClick.run() line: 17082 
    Handler.handleCallback(Message) line: 615   
    ViewRootImpl$ViewRootHandler(Handler).dispatchMessage(Message) line: 92 
    Looper.loop() line: 137 
    ActivityThread.main(String[]) line: 4856    
    Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
    Method.invoke(Object, Object...) line: 511  
    ZygoteInit$MethodAndArgsCaller.run() line: 1007 
    ZygoteInit.main(String[]) line: 774 
    NativeStart.main(String[]) line: not available [native method]  

Answer 1

我猜您尚未在 list 文件中添加 Mainactivity 或 Hallo。请发布您的 androidManifest.xml