一、让子View显示超出自身容器大小
在子View的父布局上设置android:clipChildren=“false”,在View会通过这个方法判断是否需要clip。使用的时候需要注意，这个参数只能设置在ViewGroup上，而生效的范围是ViewGroup内的子View。
void setDisplayListProperties(RenderNode renderNode) {
if (renderNode != null) {
...
renderNode.setClipToBounds(mParent instanceof ViewGroup
&& ((ViewGroup) mParent).getClipChildren());
...
}
....
}
没有添加android:clipChildren=“false”，图1的imagview是无法把图片显示完整
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="@+id/image"
android:layout_width="0dp"
android:layout_height="100dp"
android:src="@drawable/snow"
android:scaleType="centerCrop"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
添加android:clipChildren=“false”后，图2的imagview的大小是没有改变，但是可以把超出imagview范围的图片内容都显示出来。
二、取消RecyclerView滑动到边缘上的水纹提示
RecyclerView是继承ViewGroup的，而VIewGroup在初始的时候会设置WILL_NOT_DRAW进行绘制的优化，因为一般ViewGroup只是作为容器用，具体的内容应该由View来绘制。
private void initViewGroup() {
// ViewGroup doesn't draw by default
if (!debugDraw()) {
setFlags(WILL_NOT_DRAW, DRAW_MASK);
}
...
}
当然也有特殊情况，例如RecyclerView的滑动到边缘的水纹提示，这个就需要RecyclerView自身绘制，所以View也提供setWillNotDraw(boolean willNotDraw)这个方法对这个参数进行修改。
public void setWillNotDraw(boolean willNotDraw) {
setFlags(willNotDraw ? WILL_NOT_DRAW : 0, DRAW_MASK);
}
所以RecyclerView也会调用这个方法进行设置，果然在构造里调用了setWillNotDraw(boolean willNotDraw)这个方法。
public RecyclerView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
...
setWillNotDraw(getOverScrollMode() == View.OVER_SCROLL_NEVER);
...
}
需要取消水纹效果，就需要用setWillNotDraw(boolean willNotDraw)这个方法设置为true，而当getOverScrollMode() == View.OVER_SCROLL_NEVER为true的时候就不会在绘制水纹了。而这个getOverScrollMode()方法是View里自带的一个方法，所以应该还有设置的方法。 在View里面可以找到这个设置方法，可以通过在代码里设置了这个方法就可以把水纹取消。
public void setOverScrollMode(int overScrollMode) {
if (overScrollMode != OVER_SCROLL_ALWAYS &&
overScrollMode != OVER_SCROLL_IF_CONTENT_SCROLLS &&
overScrollMode != OVER_SCROLL_NEVER) {
throw new IllegalArgumentException("Invalid overscroll mode " + overScrollMode);
}
mOverScrollMode = overScrollMode;
}
其实除了可以在代码上设置之外，还可以通过xml布局的时候设置,android:overScrollMode="never"
...
case R.styleable.View_overScrollMode:
overScrollMode = a.getInt(attr, OVER_SCROLL_IF_CONTENT_SCROLLS);
break;
...
三、状态栏的设置
在style主题中设置这个 true 会导致内容显示到状态栏中。 隐藏状态栏的方法 window.decorView.windowInsetsController?.hide(WindowInsets.Type.systemBars()) 在刘海屏隐藏状态栏，会导致状态栏显示黑色，可以用下面代码解决
/**
* 适配刘海屏
* Fits notch screen.
*/
private fun fitsNotchScreen() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
val lp: WindowManager.LayoutParams = window.getAttributes()
lp.layoutInDisplayCutoutMode = WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES
window.setAttributes(lp)
}
}
四、将View提示到顶层
view.bringToFront() 方法可以将view提示到顶层
/**
* Change the view's z order in the tree, so it's on top of other sibling
* views. This ordering change may affect layout, if the parent container
* uses an order-dependent layout scheme (e.g., LinearLayout). Prior
* to {@link android.os.Build.VERSION_CODES#KITKAT} this
* method should be followed by calls to {@link #requestLayout()} and
* {@link View#invalidate()} on the view's parent to force the parent to redraw
* with the new child ordering.
*
* @see ViewGroup#bringChildToFront(View)
*/
public void bringToFront() {
if (mParent != null) {
mParent.bringChildToFront(this);
}
}
五、代码触发View的OnClickListener和OnLongClickListener、 performLongClick(float x, float y)
view.performClick() 和 view.performLongClick() 可以分别触发view的OnClickListener和OnLongClickListener事件 view.performLongClick(float x, float y)方法可以通过坐标来触发对应view的OnLongClickListener事件
/**
* Call this view's OnClickListener, if it is defined. Performs all normal
* actions associated with clicking: reporting accessibility event, playing
* a sound, etc.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
// NOTE: other methods on View should not call this method directly, but performClickInternal()
// instead, to guarantee that the autofill manager is notified when necessary (as subclasses
// could extend this method without calling super.performClick()).
public boolean performClick() {
// We still need to call this method to handle the cases where performClick() was called
// externally, instead of through performClickInternal()
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}
/**
* Calls this view's OnLongClickListener, if it is defined. Invokes the
* context menu if the OnLongClickListener did not consume the event.
*
* @return {@code true} if one of the above receivers consumed the event,
* {@code false} otherwise
*/
public boolean performLongClick() {
return performLongClickInternal(mLongClickX, mLongClickY);
}
/**
* Calls this view's OnLongClickListener, if it is defined. Invokes the
* context menu if the OnLongClickListener did not consume the event,
* anchoring it to an (x,y) coordinate.
*
* @param x x coordinate of the anchoring touch event, or {@link Float#NaN}
* to disable anchoring
* @param y y coordinate of the anchoring touch event, or {@link Float#NaN}
* to disable anchoring
* @return {@code true} if one of the above receivers consumed the event,
* {@code false} otherwise
*/
public boolean performLongClick(float x, float y) {
mLongClickX = x;
mLongClickY = y;
final boolean handled = performLongClick();
mLongClickX = Float.NaN;
mLongClickY = Float.NaN;
return handled;
}
六、编译后的R文件路径
七、Android全局实现控件变灰
看了鸿洋大神的文章，才知道原来还可以这么简单的实现全局控件变灰,有兴趣的可以去看看。下面只是我个人的学习记录。
实现的灰度的工具
做这个的时候让我想起了之前做的人脸识别，人脸识别的第一步就是将获取的图片转换成灰度图。转换成灰度图的方式是用矩阵的方式实现的。关于矩阵这里就不展开来说了，都差不多还给了大学的高数老师了，有空再复习一下。
而在Android中已经有现成封装好的矩阵转换的类ColorMatrix，通过setSaturation(float sat)方法可以转变成灰度图，实现方法可以看图1。
那么这矩阵要怎么用呢？如果是非常了解自定义view的人，应该很快就能想到Paint.setColorFilter(ColorFilter filter)这个方法，通过查看ColorFilter的继承结构图，就可以找到ColorMatrixColorFilter是通过矩阵来设置色彩的。
为什么只设置ViewGroup的灰度，其子View也会跟着变？
按照鸿洋大神的思路，自定义一个GrayFramelayout实现一个Paint，并把Paint设置到Canvas中，最后就是用GrayFramelayout替换Activity最外层的Framelayout。自此整个过程就完成了。
但是重点来了，为什么只是将最外层的Framelayout设置灰度，它的子View也会跟着被设置灰度呢？其实鸿洋大神已经给了提示，那就是dispatchDraw(canvas: Canvas?)这个方法。
带着这个问题，我重新查看了View的draw的过程，看看下面的图3。
在这里调用我们复写的dispatchDraw(canvas: Canvas?)方法，而这个方法的描述是draw the children，而我们的复写是将Paint放进了Canvas中。
override fun dispatchDraw(canvas: Canvas?) {
canvas?.saveLayer(null, mPaint, Canvas.ALL_SAVE_FLAG)
super.dispatchDraw(canvas)
canvas?.restore()
}
继续查看原生的dispatchDraw(canvas: Canvas?)方法，View的dispatchDraw(canvas: Canvas?)是一个空方法，
那看看ViewGroup的dispatchDraw(canvas: Canvas?)方法，在这里会调用drawChild(Canvas canvas, View child, long drawingTime)方法，并且把我们修改的Canvas传进了这个方法。
override fun dispatchDraw(canvas: Canvas?) {
...
for (int i = 0; i < childrenCount; i++) {
while (transientIndex >= 0 && mTransientIndices.get(transientIndex) == i) {
final View transientChild = mTransientViews.get(transientIndex);
if ((transientChild.mViewFlags & VISIBILITY_MASK) == VISIBLE ||
transientChild.getAnimation() != null) {
more |= drawChild(canvas, transientChild, drawingTime);
}
transientIndex++;
if (transientIndex >= transientCount) {
transientIndex = -1;
}
}
final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(preorderedList, children, childIndex);
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {
more |= drawChild(canvas, child, drawingTime);
}
}
while (transientIndex >= 0) {
// there may be additional transient views after the normal views
final View transientChild = mTransientViews.get(transientIndex);
if ((transientChild.mViewFlags & VISIBILITY_MASK) == VISIBLE ||
transientChild.getAnimation() != null) {
more |= drawChild(canvas, transientChild, drawingTime);
}
transientIndex++;
if (transientIndex >= transientCount) {
break;
}
}
...
}
再看看drawChild(Canvas canvas, View child, long drawingTime)这个方法，这个方法很简单，就是调用子View的draw(Canvas canvas, ViewGroup parent, long drawingTime),并把我们修改的Canvas传给子View使用。
至此，我们就明白了为什么只是修改了最外层的VIewGroup，内部的子View也会跟着修改了，这是因为所有的控件都是默认使用最外层的ViewGroup的Canvas。
