我试图扩大中心大多数listview项目。 (最终,我希望将其扩展为一种简单而轻巧的3D效果,使元素在屏幕中间时似乎会放大,而在屏幕下方时元素会缩小,总的黑色背景和文本项会放大和缩小...)

因此,我做了一个虚拟的listview,每一行都是一个textview元素。下面,我有一个自定义适配器。

我所做的唯一相关修改是:

OnCreate()中,我将以下变量传递给适配器:

int v = (listview.getLastVisiblePosition() - listview.getFirstVisiblePosition()) + 1;

在适配器的getView()中,我得到了这个:
if (position == x/2) {
        textView.setHeight(100);
    }

无论如何,这里是所有代码,我已经跳过了导入操作:(它不算太大!...大多数是相当通用的)

MainActivity.java:
    public class MainActivity extends Activity {

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

        final ListView listview = (ListView) findViewById(R.id.listview);
        String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
                "Blackberry", "WebOS", "Ubuntu", "Windows7","iPhone", "WindowsMobile",
                "Blackberry", "WebOS", "Ubuntu", "Windows7","iPhone", "WindowsMobile",
                "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X" };

        final ArrayList<String> list = new ArrayList<String>();
        for (int i = 0; i < values.length; ++i) {
            list.add(values[i]);
        }
        int v = (listview.getLastVisiblePosition() - listview.getFirstVisiblePosition()) + 1;


        final MySimpleArrayAdapter adapter = new MySimpleArrayAdapter(this, v, R.layout.row, list);
        listview.setAdapter(adapter);

        listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, final View view,
                    int position, long id) {

            }

        });
    }
}

MySimpleArrayAdapter.java
 public class MySimpleArrayAdapter extends ArrayAdapter<String> {
    private final Context context;
    private final int x;

    HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();

    public MySimpleArrayAdapter(Context context, int a, int textViewResourceId,
            List<String> objects) {
        super(context, textViewResourceId, objects);
        this.context = context;
        this.x = a;
        for (int i = 0; i < objects.size(); ++i) {
            mIdMap.put(objects.get(i), i);
        }

    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View rowView = inflater.inflate(R.layout.row, parent, false);
        TextView textView = (TextView) rowView.findViewById(R.id.textView1);

        if (position == x/2) {
            textView.setHeight(100);
        }

        return rowView;
    }

    @Override
    public long getItemId(int position) {
        String item = getItem(position);
        return mIdMap.get(item);
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }
}

此外,在我的activity_main.xml中,我只有一个listview,在“row.xml”中,我只有一个textview。

问题:为什么没有文本出现?我清楚地将列表值添加到了textview中。

为什么最上面的元素很大而不是中间的元素,我专门将其设置为中间的元素?

这是我当前代码提供的屏幕快照:

android - 放大 ListView 中的中间元素-Android?-LMLPHP

LOGCAT错误-KMDev的解决方案
10-06 17:54:02.529: E/AndroidRuntime(19596): FATAL EXCEPTION: main
10-06 17:54:02.529: E/AndroidRuntime(19596): java.lang.RuntimeException: Unable to start activity ComponentInfo{mple.finala/mple.finala.MainActivity}: java.lang.NullPointerException
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2077)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2104)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.ActivityThread.access$600(ActivityThread.java:134)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.os.Handler.dispatchMessage(Handler.java:99)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.os.Looper.loop(Looper.java:154)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.ActivityThread.main(ActivityThread.java:4624)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at java.lang.reflect.Method.invokeNative(Native Method)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at java.lang.reflect.Method.invoke(Method.java:511)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at dalvik.system.NativeStart.main(Native Method)
10-06 17:54:02.529: E/AndroidRuntime(19596): Caused by: java.lang.NullPointerException
10-06 17:54:02.529: E/AndroidRuntime(19596):    at mple.finala.MainActivity$2.onScroll(MainActivity.java:79)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.widget.AbsListView.invokeOnItemScrollListener(AbsListView.java:1297)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.widget.AbsListView.setOnScrollListener(AbsListView.java:1286)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at mple.finala.MainActivity.onCreate(MainActivity.java:58)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.Activity.performCreate(Activity.java:4479)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050)
10-06 17:54:02.529: E/AndroidRuntime(19596):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2041)
10-06 17:54:02.529: E/AndroidRuntime(19596):    ... 11 more

编辑2:

完整代码,仍然给出空异常。

http://codeviewer.org/view/code:373d

最佳答案

需要解决一些问题。

  • 您需要使用ViewHolder模式。关于ListView以及您真正需要了解的事情都在GoogleIO 2010 - The World of ListView视频中。
  • 调整getView中项目的布局并不是一个好主意,因为这会对ListView使用的 View 回收器产生负面影响。在视频中也是如此。我真的鼓励您尝试找到一种不同的方式来显示您想要显示的内容。

  • 设定文字
  • 您正在将所需项的x维度传递到Adapter的构造函数中,而不是为其提供实际的项资源ID。如果您传入正确的参数,ArrayAdapter将为您设置文本。对于使用字符串资源和默认提供的列表项布局的简单示例:
    String[] mData = getResources().getStringArray(R.array.list_examples);
    ArrayAdapter<String> mBaseAdapter =
                new ArrayAdapter<String>(context,
                                         android.R.layout.simple_list_item_1,
                                         android.R.id.text1,
                                         mListData);
    
  • 如果我是你,我只想让适配器设置文本并通过调用super来抓取项目布局,如下所示:
    @Override
    public View getView(int position, View convertView, ViewGroup viewGroup){
        convertView = super.getView(position,convertView, viewGroup);
        //other code here
    }
    

  • 如果您真的想自己做,可以使用ViewHolder模式
        //This is the ViewHolder
        static class Holder{
            TextView mText;
        }
    
    
        @Override
        public View getView(int position, View convertView, ViewGroup viewGroup){
    
             convertView = super.getView(position, convertView, viewGroup);
    
             if (convertView == null){
                  // If you reach this, it most likely means you're not supplying the
                  // adapter the layout and textview resource it needs. You can
                  // just comment out your getView override and see if your text gets
                  // displayed.
             }
    
             Holder mHolder;
             if(convertView.getTag() == null){
                mHolder = new Holder();
                mHolder.mText = (TextView)convertView.findViewById(android.R.id.text1);
                convertView.setTag(mHolder);
             } else {
                mHolder = (Holder) convertView.getTag();
             }
    
             mHolder.mText.setText(getItem(position).toString());
        }
    

    关于getXVisibleItem方法
    // These are both implemented in AdapterView which means
    // they're flat list positions
    int firstVis = mList.getFirstVisiblePosition();
    int lastVis = mList.getLastVisiblePosition();
    
    /* This is the "conversion" from flat list positions to ViewGroup child positions */
    int count = lastVis - firstVis;
    
     /*  getChildAt(pos) is implemented in ViewGroup and has a different meaning for
     *  its position values. ViewGroup tracks visible items as children and is 0 indexed.
     *  This means you'll have 0 - X positions where X is however many items it takes
     *  to fill the visible area of your screen; usually less than 10. */
     View listItem = mList.getChildAt(count - ((int)count/2)); // This will get the middle
                                                            // item for you to adjust as
                                                            // you want.
    

    要在屏幕中间找到商品,您只需要计算可见商品的数量,然后减去上面所评论的一半即可。

    设定高度实现

    您将需要在ListView上设置一个AbsListView.OnScrollListener,然后在滚动停止时将调整应用于中间项目。前任:
    mList.setOnScrollListener(new OnScrollListener(){
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState){
    
        }
    
        @Override
        public void onScroll(AbsListView view,
                             int firstVisibleItem,
                             int visibleItemCount,
                             int totalItemCount){
    
            //Note that this is called when the scroll completes.
            //It gives us the positions we want so just calculate
            //the middle item, grab it and adjust the height directly
            //or by increasing margins if the item layout_height is
            //wrap_content. I'm not positive the margins do what you
            // need, but setting the height directly should.
            LinearLayout listItem = mList // <-- Replace LinearLayout with your layout
                          .getChildAt(visibleItemCount - ((int)visibleItemCount/2));
    
            //Make sure you use the right LayoutParams for the listItem Layout
            //If your listItem is a RelativeLayout for instance, you would use:
            // listItem.setLayoutParams(
            //      new RelativeLayout.LayoutParams(LayoutParams.FILL_PARENT,
            //                                      theHeightYouWantHere));
            listItem.setLayoutParams(
                    new LinearLayout.LayoutParams(LayoutParams.FILL_PARENT,
                                                  theHeightYouWantHere));
    
            }
    });
    

    我已经对ListView和ExpandableListView做了一些tangentially related blog posts的介绍,其中有完整的代码示例,介绍了如何使用childAt策略刷新可见项目的示例代码(示例代码只是更改了项目的文本/背景颜色)。请原谅个人博客链接及其样式(它是新的,需要做更多的工作:),但是代码运行良好。

    编辑2:对于android.R.simple_list_item_1

    只要您将TextView用于项目布局(android.R.simple_list_item_1是TextView),它就可以完全满足您的要求。如果决定使用ViewGroup布局,则需要用LayoutParams方法替换item.setHeight。
    mList.setOnScrollListener(new OnScrollListener(){
        @Override
        public void onScrollStateChanged(final AbsListView view, final int scrollState){
    
        }
    
        @Override
        public void onScroll(final AbsListView view,
                             final int firstVisibleItem,
                             final int visibleItemCount,
                             final int totalItemCount){
            if (visibleItemCount != 0){
    
                 Log.i( TAG, "firstVisibleItem: "
                             + firstVisibleItem
                             + "\nvisibleItemCount: "
                             + visibleItemCount);
    
                 final int midPosition = visibleItemCount - (visibleItemCount / 2);
                 final TextView listItem = (TextView) mList.getChildAt(midPosition);
                 listItem.setHeight(500); //Only works if you're using
                                          //android.R.simple_list_item_1 since it's
                                          //not a ViewGroup, but rather a TextView
    
                 int count = visibleItemCount;
                 while (count >= 0){ // Here we need to loop through and make sure
                                     // all recycled items are returned to their
                                     // original height.
                     final TextView item = (TextView) mList.getChildAt(count);
                     if (item != null && count != midPosition){
                         item.setHeight(100);
                     }
                     count--;
                  }
            }
        }
    });
    

    10-05 22:58
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