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
以上建议对我都没用。我的用例是在ScrollView中有4个自定义ViewPagers。它们的顶部是基于纵横比测量的，其余的只是layout_height=wrap_content。我试过cybergen, Daniel López Lacalle解决方案。没有一个是完全适合我的。
我猜为什么cybergen不能在页面> 1上工作是因为它基于第1页计算寻呼机的高度，如果你进一步滚动，这是隐藏的。
cybergen和Daniel López Lacalle建议在我的情况下都有奇怪的行为:3个中的2个加载ok, 1个随机高度为0。似乎onMeasure是在儿童被填充之前被调用的。所以我想出了这两个答案加上我自己的修正:
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (getLayoutParams().height == ViewGroup.LayoutParams.WRAP_CONTENT) {
// find the first child view
View view = getChildAt(0);
if (view != null) {
// measure the first child view with the specified measure spec
view.measure(widthMeasureSpec, heightMeasureSpec);
int h = view.getMeasuredHeight();
setMeasuredDimension(getMeasuredWidth(), h);
//do not recalculate height anymore
getLayoutParams().height = h;
}
}
}
想法是让ViewPager计算子尺寸，并在ViewPager的布局参数中保存计算出的第一页高度。不要忘记将fragment的布局高度设置为wrap_content，否则你可以得到height=0。我用过这个:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal" android:layout_width="match_parent"
android:layout_height="wrap_content">
<!-- Childs are populated in fragment -->
</LinearLayout>
请注意，如果所有页面都具有相同的高度，则此解决方案非常有效。否则，你需要基于当前的子活动重新计算ViewPager的高度。我不需要它，但如果你提出解决方案，我很乐意更新答案。
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。
另一个Kotlin代码
class DynamicViewPager @JvmOverloads constructor(
context: Context,
attrs: AttributeSet? = null
) : ViewPager(context, attrs) {
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
var height = 0
(0 until childCount).forEach {
val child = getChildAt(it)
child.measure(
widthMeasureSpec,
MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED)
)
height = max(height, child.measuredHeight)
}
if (height > 0) {
super.onMeasure(
widthMeasureSpec,
MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY)
)
} else {
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}
}
}
重写你的ViewPager的onMeasure如下将使它获得它目前拥有的最大子节点的高度。
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int height = 0;
int childWidthSpec = MeasureSpec.makeMeasureSpec(
Math.max(0, MeasureSpec.getSize(widthMeasureSpec) -
getPaddingLeft() - getPaddingRight()),
MeasureSpec.getMode(widthMeasureSpec)
);
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
child.measure(childWidthSpec, MeasureSpec.UNSPECIFIED);
int h = child.getMeasuredHeight();
if (h > height) height = h;
}
if (height != 0) {
heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
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
