Android Studio顶部导航栏标题的替换

Question

android:label="new title" 

getSupportActionBar().setTitle("New Title");

Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android">
<item
    android:id="@+id/app_bar_search"
    android:icon="@drawable/ic_search_black_24dp"
    android:title="Search"
    android:label="My new title"
    app:actionViewClass="android.widget.SearchView"
    app:showAsAction="always" />
</menu>

<com.google.android.material.appbar.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/mainToolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        android:backgroundTint="@android:color/white"
        app:liftOnScroll="true"/>

</com.google.android.material.appbar.AppBarLayout>

我的活动课

    Toolbar mToolbars = findViewById(R.id.mainToolbar);
    setSupportActionBar(mToolbars);

Answer 1

Toolbar mToolbars = findViewById(R.id.mainToolbar);
setSupportActionBar(mToolbars);
getSupportActionBar().setTitle("New Title");

  val mToolbars: Toolbar = findViewById(R.id.mainToolbar)
  setSupportActionBar(mToolbars)
  supportActionBar!!.setTitle("New Title")