java - 变化扩展了 Activity 类别

Question

您好，我正在尝试在 Android 上创建我的第一个应用程序。很抱歉提出愚蠢的问题，但我很绝望。

我在 android studio 中创建了一个空白 Activity 的新应用。

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>

Java:

public class MainActivity extends AppCompatActivity {

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

然后我想将 Activity 的扩展类更改为 ListActivity:

public class MainActivity extends ListActivity {

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

当我在移动应用程序上运行它(没有其他更改)时崩溃，并出现类似“应用程序 xy 已停止”的内容。

我知道这是一些愚蠢的失败，但我不知道该如何解决。

list :

<?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>

请帮帮我。

Answer 1

决定回答而不是评论:)

问题可能与 ListActivity 相关。不扩展 AppCompatActivity并且您可能正在使用支持库中的主题。我会切换回 AppCompatActivity并使用 android.support.v4.app.ListFragment fragment 代替。

另一个问题可能是 ListActivity期望您的布局具有 ListView id 为“@android:id/list”

在我的一个应用程序中，我不想更改为 ListFragment所以我一起破解了一个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 借来的实现，这就是为什么您会看到注释掉的原因 onCreateView和 onViewCreated方法。