我已经设置了一个简单的ViewPager，它在每个页面上都有一个高度为200dp的ImageView。
这是我的寻呼机:
pager = new ViewPager(this);
pager.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));
pager.setBackgroundColor(Color.WHITE);
pager.setOnPageChangeListener(listener);
layout.addView(pager);
尽管高度设置为wrap_content，但即使imageview只有200dp，分页器也总是充满屏幕。我尝试用“200”替换寻呼机的高度，但在不同分辨率下会得到不同的结果。我无法将“dp”添加到该值。如何将200dp添加到寻呼机的布局?
当前回答
我的答案基于Daniel López Lacalle和这篇文章http://www.henning.ms/2013/09/09/viewpager-that-simply-dont-measure-up/。丹尼尔回答的问题是，在某些情况下，我的孩子的身高为零。不幸的是，解决办法是测量两次。
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int mode = MeasureSpec.getMode(heightMeasureSpec);
// Unspecified means that the ViewPager is in a ScrollView WRAP_CONTENT.
// At Most means that the ViewPager is not in a ScrollView WRAP_CONTENT.
if (mode == MeasureSpec.UNSPECIFIED || mode == MeasureSpec.AT_MOST) {
// super has to be called in the beginning so the child views can be initialized.
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int height = 0;
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
child.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
int h = child.getMeasuredHeight();
if (h > height) height = h;
}
heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
}
// super has to be called again so the new specs are treated as exact measurements
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
这也允许你在ViewPager上设置一个高度，如果你想要的话，或者只是wrap_content。
其他回答
另一种解决方案是根据PagerAdapter中的当前页面高度更新ViewPager高度。假设你用这种方式创建ViewPager页面:
@Override
public Object instantiateItem(ViewGroup container, int position) {
PageInfo item = mPages.get(position);
item.mImageView = new CustomImageView(container.getContext());
item.mImageView.setImageDrawable(item.mDrawable);
container.addView(item.mImageView, 0);
return item;
}
其中，mPages是动态添加到PagerAdapter的PageInfo结构的内部列表，CustomImageView只是常规的ImageView，覆盖onMeasure()方法，根据指定的宽度设置其高度并保持图像纵横比。
你可以在setPrimaryItem()方法中强制ViewPager的高度:
@Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
super.setPrimaryItem(container, position, object);
PageInfo item = (PageInfo) object;
ViewPager pager = (ViewPager) container;
int width = item.mImageView.getMeasuredWidth();
int height = item.mImageView.getMeasuredHeight();
pager.setLayoutParams(new FrameLayout.LayoutParams(width, Math.max(height, 1)));
}
注意数学。这修复了ViewPager不更新显示的页面(显示为空白)，当前一页的高度为零时(即CustomImageView中可绘制的空)，在两页之间每次奇怪的来回滑动。
改进丹尼尔López Lacalle回答，重写在Kotlin:
class MyViewPager(context: Context, attrs: AttributeSet): ViewPager(context, attrs) {
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
val zeroHeight = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED)
val maxHeight = children
.map { it.measure(widthMeasureSpec, zeroHeight); it.measuredHeight }
.max() ?: 0
if (maxHeight > 0) {
val maxHeightSpec = MeasureSpec.makeMeasureSpec(maxHeight, MeasureSpec.EXACTLY)
super.onMeasure(widthMeasureSpec, maxHeightSpec)
return
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}
}
我已经在几个项目中遇到过这个问题，从来没有一个完整的解决方案。所以我创建了一个WrapContentViewPager github项目作为ViewPager的替代。
https://github.com/rnevet/WCViewPager
解决方案的灵感来自这里的一些答案，但改进了:
根据当前视图(包括滚动时)动态更改ViewPager高度。 考虑像PagerTabStrip这样的“装饰”视图的高度。 考虑所有填充。
更新到支持库版本24，打破了以前的实现。
我发现了一个解决方案，它有点像这里提到的一些解决方案的合并。
其思想是测量ViewPager的当前视图。
以下是完整的代码:
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewPager.adapter = WrapHeightViewPager.CustomPagerAdapter(this)
}
}
activity_main.xml
<FrameLayout
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"
tools:context=".MainActivity">
<com.android.myapplication.WrapHeightViewPager
android:layout_width="match_parent" android:id="@+id/viewPager"
android:background="#33ff0000"
android:layout_height="wrap_content"/>
</FrameLayout>
view_pager_page.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:gravity="center"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<ImageView android:layout_width="wrap_content" android:layout_height="wrap_content"
android:src="@android:drawable/sym_def_app_icon"/>
<TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/textView"/>
</LinearLayout>
WrapHeightViewPager.kt
class WrapHeightViewPager : ViewPager {
constructor(context: Context) : super(context) {}
constructor(context: Context, attrs: AttributeSet?) : super(context, attrs) {}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
val adapter = adapter as CustomPagerAdapter?
val currentView = adapter?.currentView
if (currentView != null) {
currentView.measure(widthMeasureSpec, heightMeasureSpec)
super.onMeasure(
widthMeasureSpec,
View.MeasureSpec.makeMeasureSpec(currentView.measuredHeight, View.MeasureSpec.EXACTLY)
)
return
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}
class CustomPagerAdapter(private val context: Context) : PagerAdapter() {
var currentView: View? = null
override fun instantiateItem(parent: ViewGroup, position: Int): Any {
val inflater = LayoutInflater.from(context)
val view = inflater.inflate(R.layout.view_pager_page, parent, false)
view.textView.text = "item$position"
parent.addView(view)
return view
}
override fun setPrimaryItem(container: ViewGroup, position: Int, obj: Any) {
super.setPrimaryItem(container, position, obj)
currentView = obj as View
}
override fun destroyItem(collection: ViewGroup, position: Int, view: Any) = collection.removeView(view as View)
override fun getCount(): Int = 3
override fun isViewFromObject(view: View, obj: Any) = view === obj
override fun getPageTitle(position: Int): CharSequence? = "item $position"
}
}
如果你使用RecyclerPagerAdapter库，获取"currentView"的方法是从你设置的pager-view-holder中获取:
val item = obj as PagerViewHolder
currentView = item.itemView
我有一个类似的(但更复杂的场景)。我有一个对话框，其中包含一个ViewPager。 其中一个子页面很短，具有静态高度。 另一个子页面应该总是尽可能高。 另一个子页面包含一个ScrollView，如果ScrollView内容不需要对话框可用的全部高度，那么该页面(以及整个对话框)应该WRAP_CONTENT。
现有的答案都不完全适用于这个特定的场景。坚持住，这是一段颠簸的旅程。
void setupView() {
final ViewPager.SimpleOnPageChangeListener pageChangeListener = new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
currentPagePosition = position;
// Update the viewPager height for the current view
/*
Borrowed from https://github.com/rnevet/WCViewPager/blob/master/wcviewpager/src/main/java/nevet/me/wcviewpager/WrapContentViewPager.java
Gather the height of the "decor" views, since this height isn't included
when measuring each page's view height.
*/
int decorHeight = 0;
for (int i = 0; i < viewPager.getChildCount(); i++) {
View child = viewPager.getChildAt(i);
ViewPager.LayoutParams lp = (ViewPager.LayoutParams) child.getLayoutParams();
if (lp != null && lp.isDecor) {
int vgrav = lp.gravity & Gravity.VERTICAL_GRAVITY_MASK;
boolean consumeVertical = vgrav == Gravity.TOP || vgrav == Gravity.BOTTOM;
if (consumeVertical) {
decorHeight += child.getMeasuredHeight();
}
}
}
int newHeight = decorHeight;
switch (position) {
case PAGE_WITH_SHORT_AND_STATIC_CONTENT:
newHeight += measureViewHeight(thePageView1);
break;
case PAGE_TO_FILL_PARENT:
newHeight = ViewGroup.LayoutParams.MATCH_PARENT;
break;
case PAGE_TO_WRAP_CONTENT:
// newHeight = ViewGroup.LayoutParams.WRAP_CONTENT; // Works same as MATCH_PARENT because...reasons...
// newHeight += measureViewHeight(thePageView2); // Doesn't allow scrolling when sideways and height is clipped
/*
Only option that allows the ScrollView content to scroll fully.
Just doing this might be way too tall, especially on tablets.
(Will shrink it down below)
*/
newHeight = ViewGroup.LayoutParams.MATCH_PARENT;
break;
}
// Update the height
ViewGroup.LayoutParams layoutParams = viewPager.getLayoutParams();
layoutParams.height = newHeight;
viewPager.setLayoutParams(layoutParams);
if (position == PAGE_TO_WRAP_CONTENT) {
// This page should wrap content
// Measure height of the scrollview child
View scrollViewChild = ...; // (generally this is a LinearLayout)
int scrollViewChildHeight = scrollViewChild.getHeight(); // full height (even portion which can't be shown)
// ^ doesn't need measureViewHeight() because... reasons...
if (viewPager.getHeight() > scrollViewChildHeight) { // View pager too tall?
// Wrap view pager height down to child height
newHeight = scrollViewChildHeight + decorHeight;
ViewGroup.LayoutParams layoutParams2 = viewPager.getLayoutParams();
layoutParams2.height = newHeight;
viewPager.setLayoutParams(layoutParams2);
}
}
// Bonus goodies :)
// Show or hide the keyboard as appropriate. (Some pages have EditTexts, some don't)
switch (position) {
// This case takes a little bit more aggressive code than usual
if (position needs keyboard shown){
showKeyboardForEditText();
} else if {
hideKeyboard();
}
}
}
};
viewPager.addOnPageChangeListener(pageChangeListener);
viewPager.getViewTreeObserver().addOnGlobalLayoutListener(
new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
// http://stackoverflow.com/a/4406090/4176104
// Do things which require the views to have their height populated here
pageChangeListener.onPageSelected(currentPagePosition); // fix the height of the first page
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
viewPager.getViewTreeObserver().removeOnGlobalLayoutListener(this);
} else {
viewPager.getViewTreeObserver().removeGlobalOnLayoutListener(this);
}
}
}
);
}
...
private void showKeyboardForEditText() {
// Make the keyboard appear.
getDialog().getWindow().clearFlags(WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM);
getDialog().getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE | WindowManager.LayoutParams.SOFT_INPUT_ADJUST_PAN);
inputViewToFocus.requestFocus();
// http://stackoverflow.com/a/5617130/4176104
InputMethodManager inputMethodManager =
(InputMethodManager) getActivity().getSystemService(Context.INPUT_METHOD_SERVICE);
inputMethodManager.toggleSoftInputFromWindow(
inputViewToFocus.getApplicationWindowToken(),
InputMethodManager.SHOW_IMPLICIT, 0);
}
...
/**
* Hide the keyboard - http://stackoverflow.com/a/8785471
*/
private void hideKeyboard() {
InputMethodManager inputManager = (InputMethodManager) getActivity().getSystemService(Context.INPUT_METHOD_SERVICE);
inputManager.hideSoftInputFromWindow(inputBibleBookStart.getWindowToken(), InputMethodManager.HIDE_NOT_ALWAYS);
}
...
//https://github.com/rnevet/WCViewPager/blob/master/wcviewpager/src/main/java/nevet/me/wcviewpager/WrapContentViewPager.java
private int measureViewHeight(View view) {
view.measure(ViewGroup.getChildMeasureSpec(-1, -1, view.getLayoutParams().width), View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
return view.getMeasuredHeight();
}
非常感谢@Raanan提供的代码来测量视图和测量装饰高度。我在他的库中遇到了一些问题——动画结结巴，我认为当对话框的高度足够短时，我的ScrollView无法滚动。
