扩大listview中的中间元素 - android？
Zen*_*nis 5 android text listview zoom android-listview
我试图放大中心最listview项目.(最后,我希望将其扩展为一种简单而轻盈的3D效果,在屏幕中间放置元素时会放大,在下方放大时缩小,黑色背景和文本项目放大和缩小...)
所以,我做了一个虚拟列表视图,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:
在OnCreate(),我将以下变量传递给适配器:
int v = (listview.getLastVisiblePosition() - listview.getFirstVisiblePosition()) + 1;
在Adapter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的代码,我已经跳过了进口:(它不是那么大!......大部分是相当普遍的)
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"中我有一个textview ..
问题:为什么没有文字出现？我清楚地将列表值添加到textview中.
为什么最重要的元素是大而不是中间元素,我特意将它设置为中间元素？
这是我当前代码给出的屏幕:
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null异常.
有一些事情需要解决.
您需要使用ViewHolder模式.那些以及您真正需要了解的关于ListView的内容都在GoogleIO 2010 - The List of ListView视频中.
在getView中调整项目的布局并不是一个好主意,因为这会对ListView使用的视图回收器产生负面影响.那也是在视频中.我真的鼓励你尝试找到一种不同的方式来显示你想要显示的内容.
设置文字
您将项目所需的x维度传递给Adapter的构造函数,而不是向它提供实际的项目资源ID.如果传入正确的参数,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:
Run Code Online (Sandbox Code Playgroud)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,我只是让适配器设置文本并通过调用super来获取项目布局:
Run Code Online (Sandbox Code Playgroud)@Override public View getView(int position, View convertView, ViewGroup viewGroup){ convertView = super.getView(position,convertView, viewGroup); //other code here }
如果你真的想自己动手,那么它就是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.
要在屏幕中间找到该项目,您只需要将您的可见项目计数并减去该计数的一半,如上所述.
设置高度实施
您需要在ListView上设置AbsListView.OnScrollListener,当滚动停止时,将调整应用于中间项.例如:
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));
}
});
我已经制作了一些关于ListView和ExpandableListView的相关博客文章,其中有关于如何刷新使用childAt策略的可见项(示例代码只是更改项目的文本/背景颜色)的完整代码示例.请原谅个人博客链接及其样式(它是新的,需要更多工作:),但代码运行良好.
编辑2:对于android.R.simple_list_item_1
只要您使用TextView作为项目布局(android.R.simple_list_item_1是TextView),这就完全符合您的要求.如果您决定使用ViewGroup布局,则需要使用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--;
}
}
}
});