这个底部导航栏的特点：

1.告别xml中的item布局，一切icon、title统统绘制得出；

2.扁平化，由于icon、title都是绘制得出的，所以只需要一个view即可，无需父布局

3.为你处理好碎片切换事务，告别冗余代码，让你从此光速开发

4.不怕需求变动，拔插式体验，增删item，只需修改1行代码

5.源代码十分简单，有助于使用者开发高度适配自身需求的底部

使用方式

1.只需要到给出的github地址中拷贝BottomBar类到你的包下即可,或者自己创建一个类名字叫BottomBar，复制如下代码并导包：

public class BottomBar extends View{
private Context context;
public BottomBar(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
this.context = context;
}
//
//提供的api 并且根据api做一定的物理基础准备
//
private int containerId;
private List fragmentClassList = new ArrayList<>();
private List titleList = new ArrayList<>();
private List iconResBeforeList = new ArrayList<>();
private List iconResAfterList = new ArrayList<>();
private List fragmentList = new ArrayList<>();
private int itemCount;
private Paint paint = new Paint();
private List iconBitmapBeforeList = new ArrayList<>();
private List iconBitmapAfterList = new ArrayList<>();
private List iconRectList = new ArrayList<>();
private int currentCheckedIndex;
private int firstCheckedIndex;
private int titleColorBefore = Color.parseColor("#999999");
private int titleColorAfter = Color.parseColor("#ff5d5e");
private int titleSizeInDp = 10;
private int iconWidth = 20;
private int iconHeight = 20;
private int titleIconMargin = 5;
public BottomBar setContainer(int containerId) {
this.containerId = containerId;
return this;
}
public BottomBar setTitleBeforeAndAfterColor(String beforeResCode, String AfterResCode) {//支持"#333333"这种形式
titleColorBefore = Color.parseColor(beforeResCode);
titleColorAfter = Color.parseColor(AfterResCode);
return this;
}
public BottomBar setTitleSize(int titleSizeInDp) {
this.titleSizeInDp = titleSizeInDp;
return this;
}
public BottomBar setIconWidth(int iconWidth) {
this.iconWidth = iconWidth;
return this;
}
public BottomBar setTitleIconMargin(int titleIconMargin) {
this.titleIconMargin = titleIconMargin;
return this;
}
public BottomBar setIconHeight(int iconHeight) {
this.iconHeight = iconHeight;
return this;
}
public BottomBar addItem(Class fragmentClass, String title, int iconResBefore, int iconResAfter) {
fragmentClassList.add(fragmentClass);
titleList.add(title);
iconResBeforeList.add(iconResBefore);
iconResAfterList.add(iconResAfter);
return this;
}
public BottomBar setFirstChecked(int firstCheckedIndex) {//从0开始
this.firstCheckedIndex = firstCheckedIndex;
return this;
}
public void build() {
itemCount = fragmentClassList.size();
//预创建bitmap的Rect并缓存
//预创建icon的Rect并缓存
for (int i = 0; i < itemCount; i++) {
Bitmap beforeBitmap = getBitmap(iconResBeforeList.get(i));
iconBitmapBeforeList.add(beforeBitmap);
Bitmap afterBitmap = getBitmap(iconResAfterList.get(i));
iconBitmapAfterList.add(afterBitmap);
Rect rect = new Rect();
iconRectList.add(rect);
Class clx = fragmentClassList.get(i);
try {
Fragment fragment = (Fragment) clx.newInstance();
fragmentList.add(fragment);
} catch (InstantiationException | IllegalAccessException e) {
e.printStackTrace();
}
}
currentCheckedIndex = firstCheckedIndex;
switchFragment(currentCheckedIndex);
invalidate();
}
private Bitmap getBitmap(int resId) {
BitmapDrawable bitmapDrawable = (BitmapDrawable) context.getResources().getDrawable(resId);
return bitmapDrawable.getBitmap();
}
//
//初始化数据基础
//
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
initParam();
}
private int titleBaseLine;
private List titleXList = new ArrayList<>();
private int parentItemWidth;
private void initParam() {
if (itemCount != 0) {
//单个item宽高
parentItemWidth = getWidth() / itemCount;
int parentItemHeight = getHeight();
//图标边长
int iconWidth = dp2px(this.iconWidth);//先指定20dp
int iconHeight = dp2px(this.iconHeight);
//图标文字margin
int textIconMargin = dp2px(((float)titleIconMargin)/2);//先指定5dp，这里除以一半才是正常的margin，不知道为啥，可能是图片的原因
//标题高度
int titleSize = dp2px(titleSizeInDp);//这里先指定10dp
paint.setTextSize(titleSize);
Rect rect = new Rect();
paint.getTextBounds(titleList.get(0), 0, titleList.get(0).length(), rect);
int titleHeight = rect.height();
//从而计算得出图标的起始top坐标、文本的baseLine
int iconTop = (parentItemHeight - iconHeight - textIconMargin - titleHeight)/2;
titleBaseLine = parentItemHeight - iconTop;
//对icon的rect的参数进行赋值
int firstRectX = (parentItemWidth - iconWidth) / 2;//第一个icon的左
for (int i = 0; i < itemCount; i++) {
int rectX = i * parentItemWidth + firstRectX;
Rect temp = iconRectList.get(i);
temp.left = rectX;
temp.top = iconTop ;
temp.right = rectX + iconWidth;
temp.bottom = iconTop + iconHeight;
}
//标题(单位是个问题)
for (int i = 0; i < itemCount; i ++) {
String title = titleList.get(i);
paint.getTextBounds(title, 0, title.length(), rect);
titleXList.add((parentItemWidth - rect.width()) / 2 + parentItemWidth * i);
}
}
}
private int dp2px(float dpValue) {
float scale = context.getResources().getDisplayMetrics().density;
return (int) (dpValue * scale + 0.5f);
}
//
//根据得到的参数绘制
//
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);//这里让view自身替我们画背景 如果指定的话
if (itemCount != 0) {
//画背景
paint.setAntiAlias(false);
for (int i = 0; i < itemCount; i++) {
Bitmap bitmap = null;
if (i == currentCheckedIndex) {
bitmap = iconBitmapAfterList.get(i);
} else {
bitmap = iconBitmapBeforeList.get(i);
}
Rect rect = iconRectList.get(i);
canvas.drawBitmap(bitmap, null, rect, paint);//null代表bitmap全部画出
}
//画文字
paint.setAntiAlias(true);
for (int i = 0; i < itemCount; i ++) {
String title = titleList.get(i);
if (i == currentCheckedIndex) {
paint.setColor(titleColorAfter);
} else {
paint.setColor(titleColorBefore);
}
int x = titleXList.get(i);
canvas.drawText(title, x, titleBaseLine, paint);
}
}
}
//
//点击事件:我观察了微博和掌盟，发现down和up都在该区域内才响应
//
int target = -1;
@SuppressLint("ClickableViewAccessibility")
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN :
target = withinWhichArea((int)event.getX());
break;
case MotionEvent.ACTION_UP :
if (event.getY() < 0) {
break;
}
if (target == withinWhichArea((int)event.getX())) {
//这里触发点击事件
switchFragment(target);
currentCheckedIndex = target;
invalidate();
}
target = -1;
break;
}
return true;
//这里return super为什么up执行不到？是因为return super的值，全部取决于你是否
//clickable，当你down事件来临，不可点击，所以return false，也就是说，而且你没
//有设置onTouchListener，并且控件是ENABLE的，所以dispatchTouchEvent的返回值
//也是false，所以在view group的dispatchTransformedTouchEvent也是返回false，
//这样一来，view group中的first touch target就是空的，所以intercept标记位
//果断为false，然后就再也进不到循环取孩子的步骤了，直接调用dispatch-
// TransformedTouchEvent并传孩子为null，所以直接调用view group自身的dispatch-
// TouchEvent了
}
private int withinWhichArea(int x) { return x/parentItemWidth; }//从0开始
//
//碎片处理代码
//
private Fragment currentFragment;
//注意 这里是只支持AppCompatActivity 需要支持其他老版的 自行修改
protected void switchFragment(int whichFragment) {
Fragment fragment = fragmentList.get(whichFragment);
int frameLayoutId = containerId;
if (fragment != null) {
FragmentTransaction transaction = ((AppCompatActivity)context).getSupportFragmentManager().beginTransaction();
if (fragment.isAdded()) {
if (currentFragment != null) {
transaction.hide(currentFragment).show(fragment);
} else {
transaction.show(fragment);
}
} else {
if (currentFragment != null) {
transaction.hide(currentFragment).add(frameLayoutId, fragment);
} else {
transaction.add(frameLayoutId, fragment);
}
}
currentFragment = fragment;
transaction.commit();
}
}
}
2.xml中
android:background="#FFFFFF"
android:id="@+id/bottom_bar"
android:layout_width="match_parent"
android:layout_height="46dp"
android:layout_gravity="bottom" />
3.java代码中
BottomBar bottomBar = findViewById(R.id.bottom_bar);
bottomBar.setContainer(R.id.fl_container)
.setTitleBeforeAndAfterColor("#999999", "#ff5d5e")
.addItem(Fragment1.class,
"首页",
R.drawable.item1_before,
R.drawable.item1_after)
.addItem(Fragment2.class,
"订单",
R.drawable.item2_before,
R.drawable.item2_after)
.addItem(Fragment3.class,
"我的",
R.drawable.item3_before,
R.drawable.item3_after)
.build();

设置了容器frame layout

设置了字体选中前后的颜色

增加了item，并且给item绑定碎片，设定选中前后的drawable以及文本

就这么简单的代码，就搞定了一切！效果如下：

image.png

而如果你正常写一个底部导航栏是怎样的？

1.item布局，你还得精心设置半天

2.底部title布局，引入若干

3.title布局放到主布局中

4.java代码中要通过findViewById找到所有item

5.给所有item设置点击事件

6.点击事件内作碎片的切换

7.当你如果要增加一个item的时候，前面的又要大幅度修改，而且代码冗余程度极高

如果你对里面icon、title的位置不满意，有更多的api供你选择

setTitleSize，以dp为单位

setIconWidth，图标宽度

setIconHeight，图标高度

setTitleIconMargin，标题图标间距

setFirstChecked，设置第一个默认选中item

由于源代码简单，易于阅读，开发者更可以自行修改源码

底部导航栏设计思路

根据api中获取的参数，计算出icon、title的精确位置，并在onDraw中绘制

在onTouchEvent里，根据触摸点，获知点击区域，响应Icon、title的更改事件以及碎片的切换事件

另一个BottomBar的实战应用可以看：

再次证明了，BottomBar，实在太方便啦！