Question

所以我正在尝试使用appcompat活动在我的应用中创建一个包含工具栏（作为操作栏）的片段，以便我可以在多个视图中重复使用它。

我使用仅扩展片段的类来测试一个简单的纯文本片段，并使其工作，但要包含一个工具栏，我需要在视图中扩展 AppCompatActivity （我认为）

当我尝试将其付诸实践时，我收到一条错误消息，指出我的action_bar_fragment不是Fragment。

我失败了，因为我错过了一些基本的东西。有什么想法吗？

主要活动：

package com.example.aaron.personaldataassistant;

import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Intent;
import android.support.v7.widget.Toolbar;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.view.Menu;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

       // action_bar_fragment = (Toolbar) findViewById(R.id.action_bar_fragment);
       // setSupportActionBar(action_bar_fragment);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater mi=getMenuInflater();
        mi.inflate(R.menu.action_bar, menu);
        return super.onCreateOptionsMenu(menu);
    }

主要活动布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:id="@+id/activity_main"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.aaron.personaldataassistant.MainActivity">


    <fragment
        android:id="@+id/action_bar_fragment"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        class="com.example.aaron.personaldataassistant.action_bar_fragment"
        tools:layout="@layout/action_bar_fragment" />

</LinearLayout>

Action Bar Fragment：

package com.example.aaron.personaldataassistant;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

public class action_bar_fragment extends AppCompatActivity {

    public action_bar_fragment() {
    }

    Toolbar action_bar;

    @Nullable

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        return inflater.inflate(R.layout.action_bar_fragment, container, false);

    }


        @Override
        protected void onCreate (Bundle savedInstanceState){
            super.onCreate(savedInstanceState);
            setContentView(R.layout.action_bar_fragment);


            action_bar = (Toolbar) findViewById(R.id.action_bar);
            setSupportActionBar(action_bar);
        }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater mi = getMenuInflater();
        mi.inflate(R.menu.action_bar, menu);
        return super.onCreateOptionsMenu(menu);
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        int i = item.getItemId();

        if (i == R.id.item1) {

            Toast.makeText(action_bar_fragment.this, "Item 1", Toast.LENGTH_SHORT).show();
        } else if (i == R.id.item2) {

            Toast.makeText(action_bar_fragment.this, "Item 2", Toast.LENGTH_SHORT).show();
        } else if (i == R.id.item3) {

            Toast.makeText(action_bar_fragment.this, "Item 3", Toast.LENGTH_SHORT).show();
        }
//replace toasts with desired actions: Settings, Help and Exit. Settigns is blank, help is context-dependent, exit gives possibility to exit


        return super.onOptionsItemSelected(item);
    }


}

片段布局：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="layout.Fragment_1">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment" />

    <android.support.v7.widget.Toolbar
        android:id="@+id/action_bar"
        android:layout_width="300dp"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimaryDark"
        android:elevation="8dp"
        android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        />

</FrameLayout>

当然还有错误信息：

  --------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.aaron.personaldataassistant, PID: 2481
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.aaron.personaldataassistant/com.example.aaron.personaldataassistant.MainActivity}: android.view.InflateException: Binary XML file line #19: Binary XML file line #19: Error inflating class fragment
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
                      at android.app.ActivityThread.-wrap12(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6077)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
                   Caused by: android.view.InflateException: Binary XML file line #19: Binary XML file line #19: Error inflating class fragment
                   Caused by: android.view.InflateException: Binary XML file line #19: Error inflating class fragment
                   Caused by: android.app.Fragment$InstantiationException: Trying to instantiate a class com.example.aaron.personaldataassistant.action_bar_fragment that is not a Fragment
                      at android.app.Fragment.instantiate(Fragment.java:617)
                      at android.app.Fragment.instantiate(Fragment.java:593)
                      at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2302)
                      at android.app.FragmentController.onCreateView(FragmentController.java:98)
                      at android.app.Activity.onCreateView(Activity.java:5884)
                      at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:36)
                      at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:75)
                      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:777)
                      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
                      at android.view.LayoutInflater.rInflate(LayoutInflater.java:858)
                      at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:377)
                      at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:284)
                      at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
                      at com.example.aaron.personaldataassistant.MainActivity.onCreate(MainActivity.java:24)
                      at android.app.Activity.performCreate(Activity.java:6662)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
                      at android.app.ActivityThread.-wrap12(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6077)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
                   Caused by: java.lang.ClassCastException
                      at android.app.Fragment.instantiate(Fragment.java:618)
                      at android.app.Fragment.instantiate(Fragment.java:593) 
                      at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2302) 
                      at android.app.FragmentController.onCreateView(FragmentController.java:98) 
                      at android.app.Activity.onCreateView(Activity.java:5884) 
                      at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:36) 
                      at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:75) 
                      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:777) 
                      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727) 
                      at android.view.LayoutInflater.rInflate(LayoutInflater.java:858) 
                      at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821) 
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:518) 
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:426) 
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:377) 
                      at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:284) 
                      at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
                      at com.example.aaron.personaldataassistant.MainActivity.onCreate(MainActivity.java:24) 
                      at android.app.Activity.performCreate(Activity.java:6662) 
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
                      at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6077) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
Application terminated.

感谢您的时间。

更新

这很好，最重要的答案帮助我弄清楚在片段中做事情可能需要不同于在Activity中执行它们的方法。谷歌搜索“如何在一个片段中做X”结果几乎给了我所需的一切。现在只剩下一个问题：我将Action Bar Fragment第37行更改为

setHasOptionsMenu(true);
action_bar = (Toolbar) getView().findViewById(R.id.action_bar);

这给了我一个空对象引用，但布局肯定存在！知道发生了什么事吗？

错误消息的相关部分是：

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference

很抱歉长时间的延迟回到你身边，我有工作。这次应该更快！

我还会清理你在回复时发表的评论。

Answer 1

我遇到了这个问题，因为主题是“试图实例化一个不是片段的类”。也许我的解决方案可以帮助你。我正在使用Android Studio 2.2.3并定位API 15。

我收到了这个错误：

...
Caused by: android.app.Fragment$InstantiationException: Trying to instantiate a class com.xyz.tuv.MyFragment that is not a Fragment

因为我正在导入：

import android.support.v4.app.Fragment;

而不是

import android.app.Fragment;

从API 11开始，您可以使用常规活动（android.app.Activity）来插入片段here。但在这种情况下，您还必须使用android.app.Fragment，这与main example显示的内容相反。

Answer 2

这是因为您的预期片段不是片段而是活动，其中：

action_bar_fragment extends AppCompatActivity {

}

是一个Activity，因此您应该使用Fragment扩展action_bar_fragment：

action_bar_fragment extends Fragment {

}

请更改您的代码样式，其中action_bar_fragment应为ActionBarFragment。类名应以大写字母开头。

请阅读Creating and Using Fragments。

Answer 3

在MainActivity类中，您必须更改某些代码的顺序，它们是：

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater mi=getMenuInflater();
    mi.inflate(R.menu.action_bar, menu);
    return super.onCreateOptionsMenu(menu);
}

将其更改为：

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
  super.onCreateOptionsMenu(menu);
  MenuInflater mi = getMenuInflater();
  mi.inflate(R.menu.action_bar, menu);
  return true;

}

再试一次。

Android - 尝试实例化不是片段的类

3 个答案: