更改扩展活动类

Question

你好我试图在Android上创建我的第一个应用程序。所以对于愚蠢的问题抱歉，但我绝望。

我在android studio中创建了一个空白活动的新应用程序。

XML：

<RelativeLayout 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" android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"> 

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

</RelativeLayout> 

的Java：

public class MainActivity extends AppCompatActivity { 

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

然后我想扩展类的活动改为ListActivity：

public class MainActivity extends ListActivity { 

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

当我运行它（无其他变动）在移动应用程序崩溃的东西像“应用程序xy已停止”。

我知道这是一些愚蠢的失败，但我不知道我该如何解决它。

清单：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.kubitas.listviewapp" > 

    <application 
     android:allowBackup="true" 
     android:icon="@mipmap/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name=".MainActivity" 
      android:label="@string/app_name" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
    </application> 

</manifest> 

请帮助我。

Answer 1

ListActivity必须在名为“@android：id/list”的活动中声明一个列表。这是使用ListActivity的要求。如果您没有真正使用ListActivity，那么您需要扩展Activity或AppCompatActivity。如果你想玩一个ListActivity，然后添加一个ListView到你的布局文件中，并按照我的名字命名。

请参阅：http://developer.android.com/reference/android/app/ListActivity.html

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout 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" android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"> 

<ListView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@android:id/list" 
    android:layout_centerVertical="true" 
    android:layout_centerHorizontal="true" /> 
</RelativeLayout> 

类扩展ListActivity

public class MainActivity extends ListActivity { 

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

Answer 2

决定回答，而不是评论:)

问题可能是ListActivity不相关的事实扩展AppCompatActivity，您可能会使用支持库中的主题。我会切换回AppCompatActivity并改为使用android.support.v4.app.ListFragment片段。

另一个问题可能是ListActivity期待您的布局有一个ID的ListView“@android：ID /列表”

在我的应用程序之一，我不想更改为ListFragment如此我砍死在一起的AppCompactListActivity延伸AppCompatActivity：

import android.os.Handler; 
import android.view.View; 
import android.view.animation.AnimationUtils; 
import android.widget.AdapterView; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.TextView; 

public abstract class AppCompatListActivity extends android.support.v7.app.AppCompatActivity { 

    static final int INTERNAL_EMPTY_ID = 0x00ff0001; 
    static final int INTERNAL_PROGRESS_CONTAINER_ID = 0x00ff0002; 
    static final int INTERNAL_LIST_CONTAINER_ID = 0x00ff0003; 

    final private Handler mHandler = new Handler(); 

    final private Runnable mRequestFocus = new Runnable() { 
     public void run() { 
      mList.focusableViewAvailable(mList); 
     } 
    }; 

    final private AdapterView.OnItemClickListener mOnClickListener 
      = new AdapterView.OnItemClickListener() { 
     public void onItemClick(AdapterView<?> parent, View v, int position, long id) { 
      onListItemClick((ListView)parent, v, position, id); 
     } 
    }; 

    ListAdapter mAdapter; 
    ListView mList; 
    View mEmptyView; 
    TextView mStandardEmptyView; 
    View mProgressContainer; 
    View mListContainer; 
    CharSequence mEmptyText; 
    boolean mListShown; 

    public AppCompatListActivity() { 
    } 

    /** 
    * Provide default implementation to return a simple list view. Subclasses 
    * can override to replace with their own layout. If doing so, the 
    * returned view hierarchy <em>must</em> have a ListView whose id 
    * is {@link android.R.id#list android.R.id.list} and can optionally 
    * have a sibling view id {@link android.R.id#empty android.R.id.empty} 
    * that is to be shown when the list is empty. 
    * 
    * <p>If you are overriding this method with your own custom content, 
    * consider including the standard layout {@link android.R.layout#list_content} 
    * in your layout file, so that you continue to retain all of the standard 
    * behavior of ListFragment. In particular, this is currently the only 
    * way to have the built-in indeterminant progress state be shown. 
    */ 
    /* 
    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     FrameLayout root = new FrameLayout(context); 

     // ------------------------------------------------------------------ 

     LinearLayout pframe = new LinearLayout(context); 
     pframe.setId(INTERNAL_PROGRESS_CONTAINER_ID); 
     pframe.setOrientation(LinearLayout.VERTICAL); 
     pframe.setVisibility(View.GONE); 
     pframe.setGravity(Gravity.CENTER); 

     ProgressBar progress = new ProgressBar(context, null, 
       android.R.attr.progressBarStyleLarge); 
     pframe.addView(progress, new FrameLayout.LayoutParams(
       ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT)); 

     root.addView(pframe, new FrameLayout.LayoutParams(
       ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.FILL_PARENT)); 

     // ------------------------------------------------------------------ 

     FrameLayout lframe = new FrameLayout(context); 
     lframe.setId(INTERNAL_LIST_CONTAINER_ID); 

     TextView tv = new TextView(getActivity()); 
     tv.setId(INTERNAL_EMPTY_ID); 
     tv.setGravity(Gravity.CENTER); 
     lframe.addView(tv, new FrameLayout.LayoutParams(
       ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.FILL_PARENT)); 

     ListView lv = new ListView(getActivity()); 
     lv.setId(android.R.id.list); 
     lv.setDrawSelectorOnTop(false); 
     lframe.addView(lv, new FrameLayout.LayoutParams(
       ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.FILL_PARENT)); 

     root.addView(lframe, new FrameLayout.LayoutParams(
       ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.FILL_PARENT)); 

     // ------------------------------------------------------------------ 

     root.setLayoutParams(new FrameLayout.LayoutParams(
       ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.FILL_PARENT)); 

     return root; 
    } 

    @Override 
    public void onViewCreated(View view, Bundle savedInstanceState) { 
     super.onViewCreated(view, savedInstanceState); 
     ensureList(); 
    } 
    */ 

    /** 
    * Detach from list view. 
    */ 
    @Override 
    public void onDestroy() { 
     mHandler.removeCallbacks(mRequestFocus); 
     mList = null; 
     mListShown = false; 
     mEmptyView = mProgressContainer = mListContainer = null; 
     mStandardEmptyView = null; 
     super.onDestroy(); 
    } 

    /** 
    * This method will be called when an item in the list is selected. 
    * Subclasses should override. Subclasses can call 
    * getListView().getItemAtPosition(position) if they need to access the 
    * data associated with the selected item. 
    * 
    * @param l The ListView where the click happened 
    * @param v The view that was clicked within the ListView 
    * @param position The position of the view in the list 
    * @param id The row id of the item that was clicked 
    */ 
    public void onListItemClick(ListView l, View v, int position, long id) { 
    } 

    /** 
    * Provide the cursor for the list view. 
    */ 
    public void setListAdapter(ListAdapter adapter) { 
     boolean hadAdapter = mAdapter != null; 
     mAdapter = adapter; 
     if (mList != null) { 
      mList.setAdapter(adapter); 
      if (!mListShown && !hadAdapter) { 
       // The list was hidden, and previously didn't have an 
       // adapter. It is now time to show it. 
       //setListShown(true, getView().getWindowToken() != null); 
       setListShown(true, false); 
      } 
     } 
    } 

    /** 
    * Set the currently selected list item to the specified 
    * position with the adapter's data 
    * 
    * @param position - 
    */ 
    public void setSelection(int position) { 
     ensureList(); 
     mList.setSelection(position); 
    } 

    /** 
    * Get the position of the currently selected list item. 
    */ 
    public int getSelectedItemPosition() { 
     ensureList(); 
     return mList.getSelectedItemPosition(); 
    } 

    /** 
    * Get the cursor row ID of the currently selected list item. 
    */ 
    public long getSelectedItemId() { 
     ensureList(); 
     return mList.getSelectedItemId(); 
    } 

    /** 
    * Get the activity's list view widget. 
    */ 
    public ListView getListView() { 
     ensureList(); 
     return mList; 
    } 

    /** 
    * The default content for a ListFragment has a TextView that can 
    * be shown when the list is empty. If you would like to have it 
    * shown, call this method to supply the text it should use. 
    */ 
    public void setEmptyText(CharSequence text) { 
     ensureList(); 
     if (mStandardEmptyView == null) { 
      throw new IllegalStateException("Can't be used with a custom content view"); 
     } 
     mStandardEmptyView.setText(text); 
     if (mEmptyText == null) { 
      mList.setEmptyView(mStandardEmptyView); 
     } 
     mEmptyText = text; 
    } 

    /** 
    * Control whether the list is being displayed. You can make it not 
    * displayed if you are waiting for the initial data to show in it. During 
    * this time an indeterminant progress indicator will be shown instead. 
    * 
    * <p>Applications do not normally need to use this themselves. The default 
    * behavior of ListFragment is to start with the list not being shown, only 
    * showing it once an adapter is given with {@link #setListAdapter(ListAdapter)}. 
    * If the list at that point had not been shown, when it does get shown 
    * it will be do without the user ever seeing the hidden state. 
    * 
    * @param shown If true, the list view is shown; if false, the progress 
    * indicator. The initial value is true. 
    */ 
    public void setListShown(boolean shown) { 
     setListShown(shown, true); 
    } 

    /** 
    * Like {@link #setListShown(boolean)}, but no animation is used when 
    * transitioning from the previous state. 
    */ 
    public void setListShownNoAnimation(boolean shown) { 
     setListShown(shown, false); 
    } 

    /** 
    * Control whether the list is being displayed. You can make it not 
    * displayed if you are waiting for the initial data to show in it. During 
    * this time an indeterminant progress indicator will be shown instead. 
    * 
    * @param shown If true, the list view is shown; if false, the progress 
    * indicator. The initial value is true. 
    * @param animate If true, an animation will be used to transition to the 
    * new state. 
    */ 
    private void setListShown(boolean shown, boolean animate) { 
     ensureList(); 
     if (mProgressContainer == null) { 
      throw new IllegalStateException("Can't be used with a custom content view"); 
     } 
     if (mListShown == shown) { 
      return; 
     } 
     mListShown = shown; 
     if (shown) { 
      if (animate) { 
       mProgressContainer.startAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_out)); 
       mListContainer.startAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_in)); 
      } else { 
       mProgressContainer.clearAnimation(); 
       mListContainer.clearAnimation(); 
      } 
      mProgressContainer.setVisibility(View.GONE); 
      mListContainer.setVisibility(View.VISIBLE); 
     } else { 
      if (animate) { 
       mProgressContainer.startAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_in)); 
       mListContainer.startAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_out)); 
      } else { 
       mProgressContainer.clearAnimation(); 
       mListContainer.clearAnimation(); 
      } 
      mProgressContainer.setVisibility(View.VISIBLE); 
      mListContainer.setVisibility(View.GONE); 
     } 
    } 

    /** 
    * Get the ListAdapter associated with this activity's ListView. 
    */ 
    public ListAdapter getListAdapter() { 
     return mAdapter; 
    } 

    private void ensureList() { 
     if (mList != null) { 
      return; 
     } 

     View root = findViewById(android.R.id.content).getRootView(); 
     if (root == null) { 
      throw new IllegalStateException("Content view not yet created"); 
     } 
     if (root instanceof ListView) { 
      mList = (ListView)root; 
     } else { 
      mStandardEmptyView = (TextView)root.findViewById(INTERNAL_EMPTY_ID); 
      if (mStandardEmptyView == null) { 
       mEmptyView = root.findViewById(android.R.id.empty); 
      } else { 
       mStandardEmptyView.setVisibility(View.GONE); 
      } 
      mProgressContainer = root.findViewById(INTERNAL_PROGRESS_CONTAINER_ID); 
      mListContainer = root.findViewById(INTERNAL_LIST_CONTAINER_ID); 
      View rawListView = root.findViewById(android.R.id.list); 
      if (!(rawListView instanceof ListView)) { 
       if (rawListView == null) { 
        throw new RuntimeException(
          "Your content must have a ListView whose id attribute is " + 
            "'android.R.id.list'"); 
       } 
       throw new RuntimeException(
         "Content has view with id attribute 'android.R.id.list' " 
           + "that is not a ListView class"); 
      } 
      mList = (ListView)rawListView; 
      if (mEmptyView != null) { 
       mList.setEmptyView(mEmptyView); 
      } else if (mEmptyText != null) { 
       mStandardEmptyView.setText(mEmptyText); 
       mList.setEmptyView(mStandardEmptyView); 
      } 
     } 
     mListShown = true; 
     mList.setOnItemClickListener(mOnClickListener); 
     if (mAdapter != null) { 
      ListAdapter adapter = mAdapter; 
      mAdapter = null; 
      setListAdapter(adapter); 
     } else { 
      // We are starting without an adapter, so assume we won't 
      // have our data right away and start with the progress indicator. 
      if (mProgressContainer != null) { 
       setListShown(false, false); 
      } 
     } 
     mHandler.post(mRequestFocus); 
    } 
} 

大部分代码是从ListFragment实现这就是为什么你会看到注释掉onCreateView和onViewCreated方法借来的。