代码中的运行时异常

Question

我有这个代码来创建一个视差滚动效果，我在这段代码中找不到任何错误但是当我运行应用程序它崩溃并且它显示代码中的运行时异常，我不明白是什么问题是。任何人都可以帮忙吗？

这是我的MainActivity

public class MainActivity extends Activity {
private int lastTop = 0;
ImageView image;
ListView listView;

ArrayAdapter adapter;
ArrayList<String> items = new ArrayList<>();

public void parallax(final View v) {
    final Rect r = new Rect();
    v.getLocalVisibleRect(r);

    if (lastTop != r.top) {
        lastTop = r.top;
        v.post(new Runnable() {
            @Override
            public void run() {
                v.setY((float) (r.top / 2.0));
            }
        });
    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listView = (ListView) findViewById(R.id.listView);

    items.add("List Item 1");
    items.add("List Item 2");
    items.add("List Item 3");
    items.add("List Item 4");
    items.add("List Item 5");
    items.add("List Item 6");
    items.add("List Item 7");
    items.add("List Item 8");
    items.add("List Item 9");
    items.add("List Item 10");
    items.add("List Item 11");
    items.add("List Item 12");
    items.add("List Item 13");
    items.add("List Item 14");
    items.add("List Item 15");
    items.add("List Item 16");
    items.add("List Item 17");
    items.add("List Item 18");
    items.add("List Item 19");
    items.add("List Item 20");

    adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, items);
    listView.setAdapter(adapter);
    adapter.notifyDataSetChanged();
    View view = getLayoutInflater().inflate(R.layout.header, null, false);
    image = (ImageView) view.findViewById(R.id.image);
    listView.addHeaderView(view);
    listView.setOnScrollListener(new AbsListView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            parallax(image);
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            parallax(image);
        }
    });
}
}

这是我的logcat

java.lang.RuntimeException: Unable to start activity ComponentInfo{in.zoid.parallaxtutorial/in.zoid.parallaxtutorial.MainActivity}: java.lang.IllegalStateException: Cannot add header view to list -- setAdapter has already been called.
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
        at android.app.ActivityThread.access$700(ActivityThread.java:140)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4921)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.IllegalStateException: Cannot add header view to list -- setAdapter has already been called.
        at android.widget.ListView.addHeaderView(ListView.java:261)
        at android.widget.ListView.addHeaderView(ListView.java:290)
        at in.zoid.parallaxtutorial.MainActivity.onCreate(MainActivity.java:70)
        at android.app.Activity.performCreate(Activity.java:5206)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)

Answer 1

您已获得非法状态，因为您首先分配适配器然后分配标头。只需反转这个东西，首先分配标题，然后分配适配器，你的问题就解决了。

public class MainActivity extends Activity {
private int lastTop = 0;
ImageView image;
ListView listView;

ArrayAdapter adapter;
ArrayList<String> items = new ArrayList<>();

public void parallax(final View v) {
    final Rect r = new Rect();
    v.getLocalVisibleRect(r);

    if (lastTop != r.top) {
        lastTop = r.top;
        v.post(new Runnable() {
            @Override
            public void run() {
                v.setY((float) (r.top / 2.0));
            }
        });
    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listView = (ListView) findViewById(R.id.listView);

    items.add("List Item 1");
    items.add("List Item 2");
    items.add("List Item 3");
    items.add("List Item 4");
    items.add("List Item 5");
    items.add("List Item 6");
    items.add("List Item 7");
    items.add("List Item 8");
    items.add("List Item 9");
    items.add("List Item 10");
    items.add("List Item 11");
    items.add("List Item 12");
    items.add("List Item 13");
    items.add("List Item 14");
    items.add("List Item 15");
    items.add("List Item 16");
    items.add("List Item 17");
    items.add("List Item 18");
    items.add("List Item 19");
    items.add("List Item 20");

    View view = getLayoutInflater().inflate(R.layout.header, null, false);
    image = (ImageView) view.findViewById(R.id.image);
    listView.addHeaderView(view);

    adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, items);
    listView.setAdapter(adapter);
    adapter.notifyDataSetChanged();
    listView.setOnScrollListener(new AbsListView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            parallax(image);
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            parallax(image);
        }
    });
}

}

Answer 2

将此更改应用于您的问题解决::

public class MainActivity extends Activity {
    private int lastTop = 0;
    ImageView image;
    ListView listView;

    ArrayAdapter adapter;
    ArrayList<String> items = new ArrayList<>();

    public void parallax(final View v) {
        final Rect r = new Rect();
        v.getLocalVisibleRect(r);

        if (lastTop != r.top) {
            lastTop = r.top;
            v.post(new Runnable() {
                @Override
                public void run() {
                    v.setY((float) (r.top / 2.0));
                }
            });
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.listView);

        items.add("List Item 1");
        items.add("List Item 2");
        items.add("List Item 3");
        items.add("List Item 4");
        items.add("List Item 5");
        items.add("List Item 6");
        items.add("List Item 7");
        items.add("List Item 8");
        items.add("List Item 9");
        items.add("List Item 10");
        items.add("List Item 11");
        items.add("List Item 12");
        items.add("List Item 13");
        items.add("List Item 14");
        items.add("List Item 15");
        items.add("List Item 16");
        items.add("List Item 17");
        items.add("List Item 18");
        items.add("List Item 19");
        items.add("List Item 20");

        View view = getLayoutInflater().inflate(R.layout.header, null, false);
        image = (ImageView) view.findViewById(R.id.image);
        listView.addHeaderView(view);

        adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, items);
        listView.setAdapter(adapter);
        adapter.notifyDataSetChanged();
        listView.setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {
                parallax(image);
            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                parallax(image);
            }
        });
    }
}

Answer 3

我没有声誉，所以我只能在答案中写下我的话。 我认为你应该定义一个listview类来扩展listview，并在其中初始化headview。比如下面的代码。

public FriendCircleList(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    // TODO Auto-generated constructor stub
    initHeadView(context);
}

private void initHeadView(Context context) {
    headView = LayoutInflater.from(context).inflate(R.layout.header, null);
    addHeaderView(headView);
    circle = (ImageView) headView.findViewById(R.id.circleprogress);
    headView.getViewTreeObserver().addOnPreDrawListener(
            new OnPreDrawListener() {
                @Override
                public boolean onPreDraw() {
                    if (headView.getMeasuredHeight() > 0) {
                        headViewHeight = headView.getMeasuredHeight();
                        headView.getViewTreeObserver()
                                .removeOnPreDrawListener(this);
                    }
                    return true;
                }
            });
    setOnScrollListener(this);
    currentScrollState = OnScrollListener.SCROLL_STATE_IDLE;
    currentState = LoadState.LOADSTATE_IDLE;
    firstVisibleItem = 0;
    CircleMarginTop = 76;
    setSelector(new ColorDrawable(Color.TRANSPARENT));
    setItemsCanFocus(true);
}

另外，我认为在setadpter（）之前编写addheadview（）可能会起作用。 希望它可以帮到你。