【发布时间】：2017-02-01 21:16:48
【问题描述】：
我最近一直在研究自定义视图，并试图从位于此处的教程中制作一个具体示例：http://flavienlaurent.com/blog/2013/08/28/each-navigation-drawer-hides-a-viewdraghelper/
我将添加相关代码以防止死链接导致信息丢失。教程的作者解释了如何创建一个类似于 YouTube 的 android 应用播放器行为的 ViewDragHelper，这些是他提供的代码
activity_main.xml
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
android:id="@+id/listView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="list"
/>
<com.example.vdh.YoutubeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/youtubeLayout"
android:orientation="vertical"
android:visibility="visible">
<TextView
android:id="@+id/viewHeader"
android:layout_width="match_parent"
android:layout_height="128dp"
android:fontFamily="sans-serif-thin"
android:textSize="25sp"
android:tag="text"
android:gravity="center"
android:textColor="@android:color/white"
android:background="#AD78CC"/>
<TextView
android:id="@+id/viewDesc"
android:tag="desc"
android:textSize="35sp"
android:gravity="center"
android:text="Loreum Loreum"
android:textColor="@android:color/white"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FF00FF"/>
</com.example.vdh.YoutubeLayout>
YoutubeLayout.java
public class YoutubeLayout extends ViewGroup {
private final ViewDragHelper mDragHelper;
private View mHeaderView;
private View mDescView;
private float mInitialMotionX;
private float mInitialMotionY;
private int mDragRange;
private int mTop;
private float mDragOffset;
public YoutubeLayout(Context context) {
this(context, null);
}
public YoutubeLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
@Override
protected void onFinishInflate() {
mHeaderView = findViewById(R.id.viewHeader);
mDescView = findViewById(R.id.viewDesc);
}
public YoutubeLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mDragHelper = ViewDragHelper.create(this, 1f, new DragHelperCallback());
}
public void maximize() {
smoothSlideTo(0f);
}
boolean smoothSlideTo(float slideOffset) {
final int topBound = getPaddingTop();
int y = (int) (topBound + slideOffset * mDragRange);
if (mDragHelper.smoothSlideViewTo(mHeaderView, mHeaderView.getLeft(), y)) {
ViewCompat.postInvalidateOnAnimation(this);
return true;
}
return false;
}
private class DragHelperCallback extends ViewDragHelper.Callback {
@Override
public boolean tryCaptureView(View child, int pointerId) {
return child == mHeaderView;
}
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
mTop = top;
mDragOffset = (float) top / mDragRange;
mHeaderView.setPivotX(mHeaderView.getWidth());
mHeaderView.setPivotY(mHeaderView.getHeight());
mHeaderView.setScaleX(1 - mDragOffset / 2);
mHeaderView.setScaleY(1 - mDragOffset / 2);
mDescView.setAlpha(1 - mDragOffset);
requestLayout();
}
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
int top = getPaddingTop();
if (yvel > 0 || (yvel == 0 && mDragOffset > 0.5f)) {
top += mDragRange;
}
mDragHelper.settleCapturedViewAt(releasedChild.getLeft(), top);
}
@Override
public int getViewVerticalDragRange(View child) {
return mDragRange;
}
@Override
public int clampViewPositionVertical(View child, int top, int dy) {
final int topBound = getPaddingTop();
final int bottomBound = getHeight() - mHeaderView.getHeight() - mHeaderView.getPaddingBottom();
final int newTop = Math.min(Math.max(top, topBound), bottomBound);
return newTop;
}
}
@Override
public void computeScroll() {
if (mDragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
final int action = MotionEventCompat.getActionMasked(ev);
if (( action != MotionEvent.ACTION_DOWN)) {
mDragHelper.cancel();
return super.onInterceptTouchEvent(ev);
}
if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
mDragHelper.cancel();
return false;
}
final float x = ev.getX();
final float y = ev.getY();
boolean interceptTap = false;
switch (action) {
case MotionEvent.ACTION_DOWN: {
mInitialMotionX = x;
mInitialMotionY = y;
interceptTap = mDragHelper.isViewUnder(mHeaderView, (int) x, (int) y);
break;
}
case MotionEvent.ACTION_MOVE: {
final float adx = Math.abs(x - mInitialMotionX);
final float ady = Math.abs(y - mInitialMotionY);
final int slop = mDragHelper.getTouchSlop();
if (ady > slop && adx > ady) {
mDragHelper.cancel();
return false;
}
}
}
return mDragHelper.shouldInterceptTouchEvent(ev) || interceptTap;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
mDragHelper.processTouchEvent(ev);
final int action = ev.getAction();
final float x = ev.getX();
final float y = ev.getY();
boolean isHeaderViewUnder = mDragHelper.isViewUnder(mHeaderView, (int) x, (int) y);
switch (action & MotionEventCompat.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
mInitialMotionX = x;
mInitialMotionY = y;
break;
}
case MotionEvent.ACTION_UP: {
final float dx = x - mInitialMotionX;
final float dy = y - mInitialMotionY;
final int slop = mDragHelper.getTouchSlop();
if (dx * dx + dy * dy < slop * slop && isHeaderViewUnder) {
if (mDragOffset == 0) {
smoothSlideTo(1f);
} else {
smoothSlideTo(0f);
}
}
break;
}
}
return isHeaderViewUnder && isViewHit(mHeaderView, (int) x, (int) y) || isViewHit(mDescView, (int) x, (int) y);
}
private boolean isViewHit(View view, int x, int y) {
int[] viewLocation = new int[2];
view.getLocationOnScreen(viewLocation);
int[] parentLocation = new int[2];
this.getLocationOnScreen(parentLocation);
int screenX = parentLocation[0] + x;
int screenY = parentLocation[1] + y;
return screenX >= viewLocation[0] && screenX < viewLocation[0] + view.getWidth() &&
screenY >= viewLocation[1] && screenY < viewLocation[1] + view.getHeight();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
measureChildren(widthMeasureSpec, heightMeasureSpec);
int maxWidth = MeasureSpec.getSize(widthMeasureSpec);
int maxHeight = MeasureSpec.getSize(heightMeasureSpec);
setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, 0),
resolveSizeAndState(maxHeight, heightMeasureSpec, 0));
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
mDragRange = getHeight() - mHeaderView.getHeight();
mHeaderView.layout(
0,
mTop,
r,
mTop + mHeaderView.getMeasuredHeight());
mDescView.layout(
0,
mTop + mHeaderView.getMeasuredHeight(),
r,
mTop + b);
}
}
作者指出onLayout和onMeasure写得不好，我认为这些（或其中之一）可能是其中一个孩子出现问题的原因。
为了我的目标，我将mDescView 替换为包含相应TextView 的Framelayout 视图。他们两个都将高度设置为match_parent，并且父级（mDescView）确实正确设置了它的高度，但是它的子级（TextView inside mDescView）忽略了父级高度并拉伸以使其高度等于屏幕高度（或自定义视图高度，无法区分）。这是一个问题，因为mDescView 孩子永远不会通过match_parent 根据父母正确调整他们的身高，我一直在寻找解决方案好几天，但没有找到，通过研究我找不到原因为什么会这样。
这是这个问题的结果，请注意TextView 的高度如何大于其父级mDescView，尽管它们的高度都设置为match_parent
所以我的问题是，我怎样才能让那个父母（或任何父母）的孩子（孩子们）像他们应该的那样匹配他们父母的身高。
作为附加请求，如果可能的话，任何人都可以解释为什么作者认为他的某些方法不是最好/正确的方法，以及应该如何正确/更好地完成它们。
【问题讨论】：
标签： java android viewgroup viewdraghelper