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
我只是在回答一个非常类似的问题，在寻找一个链接来支持我的说法时，碰巧发现了这个，你很幸运:)
我的另一个回答是: ViewPager不支持wrap_content，因为它(通常)不会同时加载所有的子页面，因此无法获得适当的大小(可以选择在每次切换页面时改变大小)。
然而，你可以设置一个精确的尺寸(例如150dp)和match_parent也可以。 您还可以通过更改其LayoutParams中的height-属性，从代码中动态修改维度。
根据你的需要，你可以在它自己的xml文件中创建ViewPager, layout_height设置为200dp，然后在你的代码中，而不是从头创建一个新的ViewPager，你可以扩展这个xml文件:
LayoutInflater inflater = context.getLayoutInflater();
inflater.inflate(R.layout.viewpagerxml, layout, true);
其他回答
使用Daniel López Localle answer，我在Kotlin中创建了这个类。希望能节省你更多的时间
class DynamicHeightViewPager @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null) : ViewPager(context, attrs) {
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
var heightMeasureSpec = heightMeasureSpec
var height = 0
for (i in 0 until childCount) {
val child = getChildAt(i)
child.measure(widthMeasureSpec, View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED))
val h = child.measuredHeight
if (h > height) height = h
}
if (height != 0) {
heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height, View.MeasureSpec.EXACTLY)
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}}
另一个更通用的解决方案是让wrap_content正常工作。
我已经扩展了ViewPager来覆盖onMeasure()。高度被包裹在第一个子视图周围。如果子视图的高度不完全相同，这可能会导致意想不到的结果。因此，类可以很容易地扩展，让我们说动画到当前视图/页面的大小。但我不需要。
你可以在yout XML布局中使用这个ViewPager，就像原来的ViewPager一样:
<view
android:layout_width="match_parent"
android:layout_height="wrap_content"
class="de.cybergen.ui.layout.WrapContentHeightViewPager"
android:id="@+id/wrapContentHeightViewPager"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"/>
优点:这种方法允许在任何布局(包括RelativeLayout)中使用ViewPager来覆盖其他ui元素。
还有一个缺点:如果你想使用页边距，你必须创建两个嵌套的布局，并给内部的一个指定所需的页边距。
代码如下:
public class WrapContentHeightViewPager extends ViewPager {
/**
* Constructor
*
* @param context the context
*/
public WrapContentHeightViewPager(Context context) {
super(context);
}
/**
* Constructor
*
* @param context the context
* @param attrs the attribute set
*/
public WrapContentHeightViewPager(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// 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);
}
setMeasuredDimension(getMeasuredWidth(), measureHeight(heightMeasureSpec, view));
}
/**
* Determines the height of this view
*
* @param measureSpec A measureSpec packed into an int
* @param view the base view with already measured height
*
* @return The height of the view, honoring constraints from measureSpec
*/
private int measureHeight(int measureSpec, View view) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
result = specSize;
} else {
// set the height from the base view if available
if (view != null) {
result = view.getMeasuredHeight();
}
if (specMode == MeasureSpec.AT_MOST) {
result = Math.min(result, specSize);
}
}
return result;
}
}
这个ViewPager只调整到当前可见的子节点(不是它实际的最大子节点)
这个想法来自https://stackoverflow.com/a/56325869/4718406
public class DynamicHeightViewPager extends ViewPager {
public DynamicHeightViewPager (Context context) {
super(context);
initPageChangeListener();
}
public DynamicHeightViewPager (Context context, AttributeSet attrs) {
super(context, attrs);
initPageChangeListener();
}
private void initPageChangeListener() {
addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
requestLayout();
}
});
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//View child = getChildAt(getCurrentItem());
View child = getCurrentView(this);
if (child != null) {
child.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0,
MeasureSpec.UNSPECIFIED));
int h = child.getMeasuredHeight();
heightMeasureSpec = MeasureSpec.makeMeasureSpec(h, MeasureSpec.EXACTLY);
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
View getCurrentView(ViewPager viewPager) {
try {
final int currentItem = viewPager.getCurrentItem();
for (int i = 0; i < viewPager.getChildCount(); i++) {
final View child = viewPager.getChildAt(i);
final ViewPager.LayoutParams layoutParams = (ViewPager.LayoutParams)
child.getLayoutParams();
Field f = layoutParams.getClass().getDeclaredField("position");
//NoSuchFieldException
f.setAccessible(true);
int position = (Integer) f.get(layoutParams); //IllegalAccessException
if (!layoutParams.isDecor && currentItem == position) {
return child;
}
}
} catch (NoSuchFieldException e) {
e.fillInStackTrace();
} catch (IllegalArgumentException e) {
e.fillInStackTrace();
} catch (IllegalAccessException e) {
e.fillInStackTrace();
}
return null;
}
}
如果你需要ViewPager调整它的大小到每个子，而不仅仅是最大的一个，我写了一段代码来做这件事。注意，在这个变化上没有动画(在我的例子中没有必要)
android:minHeight标志也被支持。
public class ChildWrappingAdjustableViewPager extends ViewPager {
List<Integer> childHeights = new ArrayList<>(getChildCount());
int minHeight = 0;
int currentPos = 0;
public ChildWrappingAdjustableViewPager(@NonNull Context context) {
super(context);
setOnPageChangeListener();
}
public ChildWrappingAdjustableViewPager(@NonNull Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
obtainMinHeightAttribute(context, attrs);
setOnPageChangeListener();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
childHeights.clear();
//calculate child views
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 < minHeight) {
h = minHeight;
}
childHeights.add(i, h);
}
if (childHeights.size() - 1 >= currentPos) {
heightMeasureSpec = MeasureSpec.makeMeasureSpec(childHeights.get(currentPos), MeasureSpec.EXACTLY);
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
private void obtainMinHeightAttribute(@NonNull Context context, @Nullable AttributeSet attrs) {
int[] heightAttr = new int[]{android.R.attr.minHeight};
TypedArray typedArray = context.obtainStyledAttributes(attrs, heightAttr);
minHeight = typedArray.getDimensionPixelOffset(0, -666);
typedArray.recycle();
}
private void setOnPageChangeListener() {
this.addOnPageChangeListener(new SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
currentPos = position;
ViewGroup.LayoutParams layoutParams = ChildWrappingAdjustableViewPager.this.getLayoutParams();
layoutParams.height = childHeights.get(position);
ChildWrappingAdjustableViewPager.this.setLayoutParams(layoutParams);
ChildWrappingAdjustableViewPager.this.invalidate();
}
});
}
}
在我的例子中，当应用大小时，我需要一个带有wrap_content的viewpager来显示当前选择的元素和动画。下面您可以看到我的实现。有人能派上用场吗?
package one.xcorp.widget
import android.animation.ValueAnimator
import android.content.Context
import android.util.AttributeSet
import android.view.View
import android.view.ViewGroup.LayoutParams.MATCH_PARENT
import android.view.ViewGroup.LayoutParams.WRAP_CONTENT
import one.xcorp.widget.R
import kotlin.properties.Delegates.observable
class ViewPager : android.support.v4.view.ViewPager {
var enableAnimation by observable(false) { _, _, enable ->
if (enable) {
addOnPageChangeListener(onPageChangeListener)
} else {
removeOnPageChangeListener(onPageChangeListener)
}
}
private var animationDuration = 0L
private var animator: ValueAnimator? = null
constructor (context: Context) : super(context) {
init(context, null)
}
constructor (context: Context, attrs: AttributeSet?) : super(context, attrs) {
init(context, attrs)
}
private fun init(context: Context, attrs: AttributeSet?) {
context.theme.obtainStyledAttributes(
attrs,
R.styleable.ViewPager,
0,
0
).apply {
try {
enableAnimation = getBoolean(
R.styleable.ViewPager_enableAnimation,
enableAnimation
)
animationDuration = getInteger(
R.styleable.ViewPager_animationDuration,
resources.getInteger(android.R.integer.config_shortAnimTime)
).toLong()
} finally {
recycle()
}
}
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
val heightMode = MeasureSpec.getMode(heightMeasureSpec)
val measuredHeight = if (heightMode == MeasureSpec.EXACTLY) {
MeasureSpec.getSize(heightMeasureSpec)
} else {
val currentViewHeight = findViewByPosition(currentItem)?.also {
measureView(it)
}?.measuredHeight ?: 0
if (heightMode != MeasureSpec.AT_MOST) {
currentViewHeight
} else {
Math.min(
currentViewHeight,
MeasureSpec.getSize(heightMeasureSpec)
)
}
}
super.onMeasure(
widthMeasureSpec,
MeasureSpec.makeMeasureSpec(measuredHeight, MeasureSpec.EXACTLY)
)
}
private fun measureView(view: View) = with(view) {
val horizontalMode: Int
val horizontalSize: Int
when (layoutParams.width) {
MATCH_PARENT -> {
horizontalMode = MeasureSpec.EXACTLY
horizontalSize = this@ViewPager.measuredWidth
}
WRAP_CONTENT -> {
horizontalMode = MeasureSpec.UNSPECIFIED
horizontalSize = 0
}
else -> {
horizontalMode = MeasureSpec.EXACTLY
horizontalSize = layoutParams.width
}
}
val verticalMode: Int
val verticalSize: Int
when (layoutParams.height) {
MATCH_PARENT -> {
verticalMode = MeasureSpec.EXACTLY
verticalSize = this@ViewPager.measuredHeight
}
WRAP_CONTENT -> {
verticalMode = MeasureSpec.UNSPECIFIED
verticalSize = 0
}
else -> {
verticalMode = MeasureSpec.EXACTLY
verticalSize = layoutParams.height
}
}
val horizontalMeasureSpec = MeasureSpec.makeMeasureSpec(horizontalSize, horizontalMode)
val verticalMeasureSpec = MeasureSpec.makeMeasureSpec(verticalSize, verticalMode)
measure(horizontalMeasureSpec, verticalMeasureSpec)
}
private fun findViewByPosition(position: Int): View? {
for (i in 0 until childCount) {
val childView = getChildAt(i)
val childLayoutParams = childView.layoutParams as LayoutParams
val childPosition by lazy {
val field = childLayoutParams.javaClass.getDeclaredField("position")
field.isAccessible = true
field.get(childLayoutParams) as Int
}
if (!childLayoutParams.isDecor && position == childPosition) {
return childView
}
}
return null
}
private fun animateContentHeight(childView: View, fromHeight: Int, toHeight: Int) {
animator?.cancel()
if (fromHeight == toHeight) {
return
}
animator = ValueAnimator.ofInt(fromHeight, toHeight).apply {
addUpdateListener {
measureView(childView)
if (childView.measuredHeight != toHeight) {
animateContentHeight(childView, height, childView.measuredHeight)
} else {
layoutParams.height = animatedValue as Int
requestLayout()
}
}
duration = animationDuration
start()
}
}
private val onPageChangeListener = object : OnPageChangeListener {
override fun onPageScrollStateChanged(state: Int) {
/* do nothing */
}
override fun onPageScrolled(
position: Int,
positionOffset: Float,
positionOffsetPixels: Int
) {
/* do nothing */
}
override fun onPageSelected(position: Int) {
if (!isAttachedToWindow) {
return
}
findViewByPosition(position)?.let { childView ->
measureView(childView)
animateContentHeight(childView, height, childView.measuredHeight)
}
}
}
}
在项目中添加attrs.xml:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="ViewPager">
<attr name="enableAnimation" format="boolean" />
<attr name="animationDuration" format="integer" />
</declare-styleable>
</resources>
和使用:
<one.xcorp.widget.ViewPager
android:id="@+id/wt_content"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:enableAnimation="true" />
