Question

以下是ListFragment的程序。它不会显示任何错误但不会运行。错误日志显示消息Fatal Exception:Main...当我在模拟器上打开时，它显示“很遗憾，listfragment2已停止”。

Frament1.java代码

package com.example.listfragmentexample2;

import android.annotation.TargetApi;
import android.app.ListFragment;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class Fragment1 extends ListFragment {
    String[] presidents = {
            "Dwight D. Eisenhower",
            "John F. Kennedy",
            "Lyndon B. Johnson",
            "Richard Nixon",
            "Gerald Ford",
            "Jimmy Carter",
            "Ronald Reagan",
            "George H. W. Bush",
            "Bill Clinton",
            "George W. Bush",
            "Barack Obama"
    };
    @Override
    public View onCreateView(LayoutInflater inflater, 
            ViewGroup container, Bundle savedInstanceState) { 
        return inflater.inflate(R.layout.fragment1, container, false);
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setListAdapter(new ArrayAdapter<String>(getActivity(),
                android.R.layout.simple_list_item_1, presidents));
    }

    public void onListItemClick(ListView parent, View v, 
            int position, long id) 
    { 
        Toast.makeText(getActivity(), 
                "You have selected " + presidents[position], 
                Toast.LENGTH_SHORT).show();
    } 
}

activitymain.xml代码：

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

    <fragment
        android:id="@+id/fragment1"
        android:name="com.example.listfragmentexample2.Fragment1"
        android:layout_width="0dp"
        android:layout_height="200dp"
        android:layout_weight="0.5" />
    <fragment
        android:id="@+id/fragment2"
        android:name="com.example.listfragmentexample2.Fragment1"
        android:layout_width="0dp"
        android:layout_height="300dp"
        android:layout_weight="0.5" />

</LinearLayout>

fragment1.xml代码

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

    <ListView
        android:id="@id/android:list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:drawSelectorOnTop="false" />

</LinearLayout>

以下是错误日志：

03-05 17:51:24.935: E/AndroidRuntime(755): FATAL EXCEPTION: main
03-05 17:51:24.935: E/AndroidRuntime(755): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.listfragmentexample2/com.example.listfragmentexample2.Fragment1}: java.lang.ClassCastException: com.example.listfragmentexample2.Fragment1 cannot be cast to android.app.Activity
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.ActivityThread.access$600(ActivityThread.java:130)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.os.Looper.loop(Looper.java:137)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.ActivityThread.main(ActivityThread.java:4745)
03-05 17:51:24.935: E/AndroidRuntime(755):  at java.lang.reflect.Method.invokeNative(Native Method)
03-05 17:51:24.935: E/AndroidRuntime(755):  at java.lang.reflect.Method.invoke(Method.java:511)
03-05 17:51:24.935: E/AndroidRuntime(755):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-05 17:51:24.935: E/AndroidRuntime(755):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-05 17:51:24.935: E/AndroidRuntime(755):  at dalvik.system.NativeStart.main(Native Method)
03-05 17:51:24.935: E/AndroidRuntime(755): Caused by: java.lang.ClassCastException: com.example.listfragmentexample2.Fragment1 cannot be cast to android.app.Activity
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
03-05 17:51:24.935: E/AndroidRuntime(755):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
03-05 17:51:24.935: E/AndroidRuntime(755):  ... 11 more
)

Answer 1

Caused by: java.lang.ClassNotFoundException: com.example.listfragmentexample2.MainActivity

确保清单文件和代码中的包名和类名一致。

Manifest说应该有一个名为com.example.listfragmentexample2.MainActivity的类，但是在二进制包中找不到它。如果你确定你有它，那就清理并重建，以防早期出现构建故障。

更新了更新问题的答案：

com.example.listfragmentexample2.Fragment1 cannot be cast to android.app.Activity

您的Fragment1在清单中被宣布为activity，但它不是extends Activity。只应将活动列为清单中的活动。片段需要一个活动来托管它们。

Answer 2

你需要在onCreateView方法之后设置适配器

        public class Fragment1 extends ListFragment {
     String[] presidents = {
      "Dwight D. Eisenhower",
     "John F. Kennedy",
       "Lyndon B. Johnson",
        "Richard Nixon",
       "Gerald Ford",
        "Jimmy Carter",
      "Ronald Reagan",
      "George H. W. Bush",
      "Bill Clinton",
      "George W. Bush",
      "Barack Obama"
         };
        @Override
     public View onCreateView(LayoutInflater inflater, 
      ViewGroup container, Bundle savedInstanceState) { 
     return inflater.inflate(R.layout.fragment1, container, false);

        }

    @Override
    protected void onStart() {
 setListAdapter(new ArrayAdapter<String>(getActivity(),
       android.R.layout.simple_list_item_1, presidents));

        super.onStart();
    }
        @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

          }

        public void onListItemClick(ListView parent, View v, 
         int position, long id) 
          { 
            Toast.makeText(getActivity(), 
         "You have selected " + presidents[position], 
            Toast.LENGTH_SHORT).show();
            } 
            }

Answer 3

我认为您忘记在setContentView(R.layout.activity_main);方法中添加onCreate()。

为什么我的程序没有运行？

3 个答案: