Toolbar

一、Toolbar显示返回按钮：

setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);

二、监听

  // 重写 onOptionsItemSelected 方法
    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        if (item.getItemId() == android.R.id.home) {
            finish();
        }
        return super.onOptionsItemSelected(item);
    }

三、文字居中

        toolbar.setTitle("专题");
        TextView titleview = (TextView) toolbar.getChildAt(0);
        titleview.getLayoutParams().width= ConstraintLayout.LayoutParams.MATCH_PARENT;
        titleview.setGravity(Gravity.CENTER_HORIZONTAL);

四、Toolbar的选项菜单

@Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_options, menu);
        return super.onCreateOptionsMenu(menu);
    }

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item android:id="@+id/item1" app:showAsAction="always" android:title="" android:icon="@drawable/ic_news_detail_search"/>
    <item android:id="@+id/item2" app:showAsAction="always" android:title="" android:icon="@drawable/ic_news_detail_like_no"/>
    <item android:id="@+id/item3" app:showAsAction="always" android:title="" android:icon="@drawable/ic_news_detail_collect_no"/>
    <item android:id="@+id/item4" app:showAsAction="always" android:title="" android:icon="@drawable/ic_news_detail_share"/>
</menu>