中间凹陷的 BottomNavigationView（请滑倒最底部直接复制使用）
简书地址：
https://www.jianshu.com/p/04c44a882332
直接上代码
注：使用时一定先指定Background为透明色
添加menu为奇数个，最中间item的icon title都为空
xml：
<?xml version=”1.0″ encoding=”utf-8″?>
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:orientation=”vertical”
android:layout_width=”match_parent”
android:layout_height=”match_parent”
android:background=”#00BCD4″>
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
app:layout_constraintStart_toStartOf=”parent”
app:layout_constraintEnd_toEndOf=”parent”
android:background=”#00FFFFFF”
app:menu=”@menu/navigation”
app:layout_constraintBottom_toBottomOf=”parent”/>
</androidx.constraintlayout.widget.ConstraintLayout>
Menu：
<?xml version=”1.0″ encoding=”utf-8″?>
<menu xmlns:android=”http://schemas.android.com/apk/res/android”>
android:id=”@+id/navigation_home”
android:icon=”@drawable/nav_selector_home”
android:title=”首页” />
android:id=”@+id/navigation_find”
android:icon=”@drawable/nav_selector_find”
android:title=”发现” />
android:id=”@+id/navigation_null”
android:icon=”@null”
android:title=”@null”
/>
android:id=”@+id/navigation_message”
android:icon=”@drawable/nav_selector_message”
android:title=”消息” />
android:id=”@+id/navigation_mine”
android:icon=”@drawable/nav_selector_mine”
android:title=”我的” />
</menu>
GapNavigationView类：
注：需先自行导入 BottomNavigationView
public class GapNavigationView extends BottomNavigationView {
Contextcontext;
public GapNavigationView(Context context) {
super(context);
this.context = context;
}
public GapNavigationView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public GapNavigationView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@SuppressLint(“DrawAllocation”)
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
setLayerType(View.LAYER_TYPE_SOFTWARE, null);
//将中间类圆区域间距设置为总高度的 3/4
int centerRadius = getHeight() *3/4;
//设置阴影大小
float shadowLength =5f;
//创建画笔
Paint paint =new Paint();
//画笔抗锯齿
paint.setAntiAlias(true);
//创建路径
Path path =new Path();
//开始画View
//将起点设置在阴影之下
path.moveTo(0, shadowLength);
//凹陷部分
path.lineTo(getWidth() /2f – centerRadius, shadowLength);
path.lineTo(getWidth()/2f – centerRadius/3f *2f ,shadowLength + centerRadius/4f);
path.lineTo(getWidth()/2f – centerRadius/4f ,shadowLength + centerRadius *3/4f);
path.lineTo(getWidth()/2f + centerRadius/4f ,shadowLength + centerRadius *3/4f);
path.lineTo(getWidth()/2f + centerRadius/3f *2f ,shadowLength + centerRadius/4f);
path.lineTo(getWidth()/2f + centerRadius,shadowLength);
//封闭区域
path.lineTo(getWidth(), shadowLength);
path.lineTo(getWidth(), getHeight());
path.lineTo(0, getHeight());
path.lineTo(0, shadowLength);
path.close();
//设置挂角处的圆角角度
paint.setPathEffect(new CornerPathEffect(centerRadius /4f));
//画阴影
paint.setStyle(Paint.Style.STROKE);
paint.setColor(Color.GRAY);
paint.setStrokeWidth(1);
paint.setMaskFilter(new BlurMaskFilter(shadowLength -1, BlurMaskFilter.Blur.NORMAL));
canvas.drawPath(path, paint);
//填充背景
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
paint.setStrokeWidth(1);
paint.setMaskFilter(null);
canvas.drawPath(path, paint);
}
}
没有对它进行封装，代码很少，注释很多，根据注释修改需求即可！
到这里凹陷导航栏已经完成了，除了样子不同于 BottomNavigationView ，其余与 NavigationView 是一摸一样的 。
但是这里有个小bug，如果开启动画观察效果，你会发现当我点击导航栏底部中间时，同样时有效的，其余按钮的缩小动画会触发，因为中部本身为null，所以我们看不见。这种体验肯定是很差的，那么我们就需要屏蔽掉中间按钮的点击事件，如何屏蔽，只有看源码了～
BottomNavigationView源码分析
首先从我们的
BottomNavigationView
类入手
BottomNavigationView
发现有一些属性 比较重要的三个 :
menu
menuView
presenter
, 看名字大概是MVP模式写的吧，不过不重要～
分析一下这几个属性，我猜真实的点击在
menuView
里面（初始化在第三个构造函数里），那我们点进
BottomNavigationMenuView
看一下
果然发现了几个名字让我心潮澎湃的属性
onClickListener
itemPool
buttons
itemPool
只是一个存放了多个
BottomNavigationItemView
的池子
，
没有实际操作意义
，buttons
是
BottomNavigationItemView
的数组吗，
onClickListener
就是View的监听器，点击事件应该就在它里面！我们去看它在哪里被赋值，进入构造函数看看
构造函数
果然在这里被赋值了，点击之后的事件在这里被消费，里面有view参数可以用来判断点击的是哪个button，那我只要能改变这个 onClickListener 再里面加上判断是否为中间按钮不就大功告成了吗？
但是问题来了，这个属性是private！google 不希望我们修改它～于是我想到了反射，利用反射打开权限，赋给 onClickListener 自定义的值不就可以了？（前面 NavigationView 里的 menuView也是私有，也需要反射再写个BottomNavigationMenuView的衍生类）
于是我真的这么做了！但是很遗憾 ，没有成功，所以
没用的代码
我就不贴了。
放弃
menuView
，我们去看看
BottomNavigationView
的
menu
属性 ，它是
MenuBuilder
类 ，我们不熟这个类是做什么的，但大概猜出是个menu相关的构造类，我们找一下
menu
在哪里被赋值，发现就在构造函数里
BottomNavigation构造函数
这名字取得太明显了吧
CallBack
都出来了 ，里面实现了
onMenuItemSelected
和
onMenuModeChange
两
个方法，选中时作了一个判空操作和一个是否是当前选项，
不管是否通过判断都是有一个
onNavigationItemSelected（onNavigationItemReselected）
操作
，
所以都将事件传递给了以下两个监听者
，
返回
true
和
false
代表已处理点击和未处理点击
BottomNavigationView属性
现在我们知道这里可以处理点击事件，那只要我们在它执行判断前再判断一次是否为中间按钮，是就直接返回true不就完成了吗？
说干就干，同样的这里的
menu
是私有属性，我们可以使用反射将
menu
的callBack设置成我们刚才想要的，但是考虑到反射严重影响程序执行效率，我选择直接将 BottomNavigationView 源码 copy 下来修改。
以下是主要修改部分：
主要修改部分
其余修改部分：
1.styleble根据IDE提示导入
2.红线部分名字修改
完整GapBottomNavigationView类代码（直接复制使用）
@SuppressLint(“RestrictedApi”)
public class GapBottomNavigationViewextends FrameLayout {
private static final int MENU_PRESENTER_ID =1;
private final MenuBuildermenu;
private final BottomNavigationMenuViewmenuView;
private final BottomNavigationPresenterpresenter;
private MenuInflatermenuInflater;
private BottomNavigationView.OnNavigationItemSelectedListenerselectedListener;
private BottomNavigationView.OnNavigationItemReselectedListenerreselectedListener;
public GapBottomNavigationView(Context context) {
this(context, (AttributeSet)null);
}
public GapBottomNavigationView(Context context, AttributeSet attrs) {
this(context, attrs, attr.bottomNavigationStyle);
}
public GapBottomNavigationView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
this.presenter =new BottomNavigationPresenter();
this.menu =new BottomNavigationMenu(context);
this.menuView =new BottomNavigationMenuView(context);
LayoutParams params =new LayoutParams(-2, -2);
params.gravity =17;
this.menuView.setLayoutParams(params);
this.presenter.setBottomNavigationMenuView(this.menuView);
this.presenter.setId(1);
this.menuView.setPresenter(this.presenter);
this.menu.addMenuPresenter(this.presenter);
this.presenter.initForMenu(this.getContext(), this.menu);
TintTypedArray a = ThemeEnforcement.obtainTintedStyledAttributes(context, attrs, styleable.BottomNavigationView, defStyleAttr, style.Widget_Design_BottomNavigationView, new int[]{styleable.BottomNavigationView_itemTextAppearanceInactive, styleable.BottomNavigationView_itemTextAppearanceActive});
if (a.hasValue(styleable.BottomNavigationView_itemIconTint)) {
this.menuView.setIconTintList(a.getColorStateList(styleable.BottomNavigationView_itemIconTint));
}else {
this.menuView.setIconTintList(this.menuView.createDefaultColorStateList(16842808));
}
this.setItemIconSize(a.getDimensionPixelSize(styleable.BottomNavigationView_itemIconSize, this.getResources().getDimensionPixelSize(dimen.design_bottom_navigation_icon_size)));
if (a.hasValue(styleable.BottomNavigationView_itemTextAppearanceInactive)) {
this.setItemTextAppearanceInactive(a.getResourceId(styleable.BottomNavigationView_itemTextAppearanceInactive, 0));
}
if (a.hasValue(styleable.BottomNavigationView_itemTextAppearanceActive)) {
this.setItemTextAppearanceActive(a.getResourceId(styleable.BottomNavigationView_itemTextAppearanceActive, 0));
}
if (a.hasValue(styleable.BottomNavigationView_itemTextColor)) {
this.setItemTextColor(a.getColorStateList(styleable.BottomNavigationView_itemTextColor));
}
if (a.hasValue(styleable.BottomNavigationView_elevation)) {
ViewCompat.setElevation(this, (float) a.getDimensionPixelSize(styleable.BottomNavigationView_elevation, 0));
}
this.setLabelVisibilityMode(a.getInteger(styleable.BottomNavigationView_labelVisibilityMode, -1));
this.setItemHorizontalTranslationEnabled(a.getBoolean(styleable.BottomNavigationView_itemHorizontalTranslationEnabled, true));
int itemBackground = a.getResourceId(styleable.BottomNavigationView_itemBackground, 0);
this.menuView.setItemBackgroundRes(itemBackground);
if (a.hasValue(styleable.BottomNavigationView_menu)) {
this.inflateMenu(a.getResourceId(styleable.BottomNavigationView_menu, 0));
}
a.recycle();
this.addView(this.menuView, params);
if (VERSION.SDK_INT <21) {
this.addCompatibilityTopDivider(context);
}
this.menu.setCallback(new Callback() {
public boolean onMenuItemSelected(MenuBuilder menu, MenuItem item) {
//menu必须为奇数个
if (menu.size() %2 !=0) {
//屏蔽中间按钮的点击事件
if ( menu.getItem(menu.size()/2).equals(item)) {
return true;
}
}
if (GapBottomNavigationView.this.reselectedListener !=null && item.getItemId() == GapBottomNavigationView.this.getSelectedItemId()) {
GapBottomNavigationView.this.reselectedListener.onNavigationItemReselected(item);
return true;
}else {
return GapBottomNavigationView.this.selectedListener !=null && !GapBottomNavigationView.this.selectedListener.onNavigationItemSelected(item);
}
}
public void onMenuModeChange(MenuBuilder menu) {
}
});
}
public void setOnNavigationItemSelectedListener(@Nullable BottomNavigationView.OnNavigationItemSelectedListener listener) {
this.selectedListener = listener;
}
public void setOnNavigationItemReselectedListener(@Nullable BottomNavigationView.OnNavigationItemReselectedListener listener) {
this.reselectedListener = listener;
}
@NonNull
public MenugetMenu() {
return this.menu;
}
public void inflateMenu(int resId) {
this.presenter.setUpdateSuspended(true);
this.getMenuInflater().inflate(resId, this.menu);
this.presenter.setUpdateSuspended(false);
this.presenter.updateMenuView(true);
}
public int getMaxItemCount() {
return 5;
}
@Nullable
public ColorStateListgetItemIconTintList() {
return this.menuView.getIconTintList();
}
public void setItemIconTintList(@Nullable ColorStateList tint) {
this.menuView.setIconTintList(tint);
}
public void setItemIconSize(@Dimension int iconSize) {
this.menuView.setItemIconSize(iconSize);
}
public void setItemIconSizeRes(@DimenRes int iconSizeRes) {
this.setItemIconSize(this.getResources().getDimensionPixelSize(iconSizeRes));
}
@Dimension
public int getItemIconSize() {
return this.menuView.getItemIconSize();
}
@Nullable
public ColorStateListgetItemTextColor() {
return this.menuView.getItemTextColor();
}
public void setItemTextColor(@Nullable ColorStateList textColor) {
this.menuView.setItemTextColor(textColor);
}
/**
* @deprecated
*/
@Deprecated
@DrawableRes
public int getItemBackgroundResource() {
return this.menuView.getItemBackgroundRes();
}
public void setItemBackgroundResource(@DrawableRes int resId) {
this.menuView.setItemBackgroundRes(resId);
}
@Nullable
public DrawablegetItemBackground() {
return this.menuView.getItemBackground();
}
public void setItemBackground(@Nullable Drawable background) {
this.menuView.setItemBackground(background);
}
@IdRes
public int getSelectedItemId() {
return this.menuView.getSelectedItemId();
}
public void setSelectedItemId(@IdRes int itemId) {
MenuItem item =this.menu.findItem(itemId);
if (item !=null && !this.menu.performItemAction(item, this.presenter, 0)) {
item.setChecked(true);
}
}
public void setLabelVisibilityMode(int labelVisibilityMode) {
if (this.menuView.getLabelVisibilityMode() != labelVisibilityMode) {
this.menuView.setLabelVisibilityMode(labelVisibilityMode);
this.presenter.updateMenuView(false);
}
}
public int getLabelVisibilityMode() {
return this.menuView.getLabelVisibilityMode();
}
public void setItemTextAppearanceInactive(@StyleRes int textAppearanceRes) {
this.menuView.setItemTextAppearanceInactive(textAppearanceRes);
}
@StyleRes
public int getItemTextAppearanceInactive() {
return this.menuView.getItemTextAppearanceInactive();
}
public void setItemTextAppearanceActive(@StyleRes int textAppearanceRes) {
this.menuView.setItemTextAppearanceActive(textAppearanceRes);
}
@StyleRes
public int getItemTextAppearanceActive() {
return this.menuView.getItemTextAppearanceActive();
}
public void setItemHorizontalTranslationEnabled(boolean itemHorizontalTranslationEnabled) {
if (this.menuView.isItemHorizontalTranslationEnabled() != itemHorizontalTranslationEnabled) {
this.menuView.setItemHorizontalTranslationEnabled(itemHorizontalTranslationEnabled);
this.presenter.updateMenuView(false);
}
}
public boolean isItemHorizontalTranslationEnabled() {
return this.menuView.isItemHorizontalTranslationEnabled();
}
private void addCompatibilityTopDivider(Context context) {
View divider =new View(context);
divider.setBackgroundColor(ContextCompat.getColor(context, color.design_bottom_navigation_shadow_color));
LayoutParams dividerParams =new LayoutParams(-1, this.getResources().getDimensionPixelSize(dimen.design_bottom_navigation_shadow_height));
divider.setLayoutParams(dividerParams);
this.addView(divider);
}
private MenuInflatergetMenuInflater() {
if (this.menuInflater ==null) {
this.menuInflater =new SupportMenuInflater(this.getContext());
}
return this.menuInflater;
}
protected ParcelableonSaveInstanceState() {
Parcelable superState =super.onSaveInstanceState();
GapBottomNavigationView.SavedState savedState =new GapBottomNavigationView.SavedState(superState);
savedState.menuPresenterState =new Bundle();
this.menu.savePresenterStates(savedState.menuPresenterState);
return savedState;
}
protected void onRestoreInstanceState(Parcelable state) {
if (!(stateinstanceof GapBottomNavigationView.SavedState)) {
super.onRestoreInstanceState(state);
}else {
GapBottomNavigationView.SavedState savedState = (GapBottomNavigationView.SavedState) state;
super.onRestoreInstanceState(savedState.getSuperState());
this.menu.restorePresenterStates(savedState.menuPresenterState);
}
}
static class SavedStateextends AbsSavedState {
BundlemenuPresenterState;
public static final CreatorCREATOR =new ClassLoaderCreator() {
public GapBottomNavigationView.SavedStatecreateFromParcel(Parcel in, ClassLoader loader) {
return new GapBottomNavigationView.SavedState(in, loader);
}
public GapBottomNavigationView.SavedStatecreateFromParcel(Parcel in) {
return new GapBottomNavigationView.SavedState(in, (ClassLoader)null);
}
public GapBottomNavigationView.SavedState[]newArray(int size) {
return new GapBottomNavigationView.SavedState[size];
}
};
public SavedState(Parcelable superState) {
super(superState);
}
public SavedState(Parcel source, ClassLoader loader) {
super(source, loader);
this.readFromParcel(source, loader);
}
public void writeToParcel(@NonNull Parcel out, int flags) {
super.writeToParcel(out, flags);
out.writeBundle(this.menuPresenterState);
}
private void readFromParcel(Parcel in, ClassLoader loader) {
this.menuPresenterState = in.readBundle(loader);
}
}
public interface OnNavigationItemReselectedListener {
void onNavigationItemReselected(@NonNull MenuItem var1);
}
public interface OnNavigationItemSelectedListener {
boolean onNavigationItemSelected(@NonNull MenuItem var1);
}
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@SuppressLint(“DrawAllocation”)
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//setLayerType(View.LAYER_TYPE_SOFTWARE, null);
int centerRadius = getHeight() *3 /4;
float shadowLength =5f;
Paint paint =new Paint();
paint.setAntiAlias(true);
Path path =new Path();
path.moveTo(0, shadowLength);
path.lineTo(getWidth() /2f – centerRadius, shadowLength);
path.lineTo(getWidth() /2f – centerRadius /3f *2f, shadowLength + centerRadius /4f);
path.lineTo(getWidth() /2f – centerRadius /4f, shadowLength + centerRadius *3 /4f);
path.lineTo(getWidth() /2f + centerRadius /4f, shadowLength + centerRadius *3 /4f);
path.lineTo(getWidth() /2f + centerRadius /3f *2f, shadowLength + centerRadius /4f);
path.lineTo(getWidth() /2f + centerRadius, shadowLength);
path.lineTo(getWidth(), shadowLength);
path.lineTo(getWidth(), getHeight());
path.lineTo(0, getHeight());
path.lineTo(0, shadowLength);
path.close();
paint.setPathEffect(new CornerPathEffect(centerRadius /4f));
//画阴影
paint.setStyle(Paint.Style.STROKE);
paint.setColor(Color.GRAY);
paint.setStrokeWidth(1);
//paint.setMaskFilter(new BlurMaskFilter(shadowLength – 1, BlurMaskFilter.Blur.NORMAL));
canvas.drawPath(path, paint);
//填充白色
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
paint.setStrokeWidth(1);
paint.setMaskFilter(null);
canvas.drawPath(path, paint);
}
}
完美收工～喜欢记得点赞哦～