Question

我绝对是Android的初学者。现在我正在学习如何布局Android应用程序。所以我开始使用导航抽屉和工具栏一起使用。现在我正在创建没有默认功能的自定义操作。但它没有用。

这是我的主要活动布局

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- This LinearLayout represents the contents of the screen  -->

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <!-- The ActionBar displayed at the top -->
        <include
            layout="@layout/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

        <!-- The main content view where fragments are loaded -->
        <FrameLayout
            android:id="@+id/flContent"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>

    <!-- The navigation drawer that comes from the left -->
    <!-- Note that `android:layout_gravity` needs to be set to 'start' -->
    <android.support.design.widget.NavigationView
        android:id="@+id/nvView"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:background="@android:color/white"
        app:menu="@menu/drawer_view" />
</android.support.v4.widget.DrawerLayout>

这是我的工具栏布局

<android.support.v7.widget.Toolbar
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/toolbar"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:fitsSystemWindows="true"
    android:minHeight="?attr/actionBarSize"
    app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    android:background="?attr/colorPrimaryDark">

</android.support.v7.widget.Toolbar>

这是我的活动课

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

这是风格

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>
    <style name="AppTheme.NoActionBar">
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
    </style>
    <style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
    <style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />

但是当我开始活动时，即使我没有像布局中那样在布局中定义，也可以在操作栏中包含查看菜单项的标题和选项。

所以我想要做的是我想用我的自定义工具栏完全替换操作栏，我想删除默认行为。

所以我尝试在活动中以这种方式删除标题

setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        ActionBar actionBar = getSupportActionBar();
        actionBar.setTitle("");
        setSupportActionBar(toolbar);

但是它正在抛出错误

这是logcat

01-23 12:28:45.945 2972-2972/? D/AndroidRuntime: Shutting down VM
01-23 12:28:45.945 2972-2972/? W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xa614a908)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime: FATAL EXCEPTION: main
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.waiyanhein.todo.todo/com.waiyanhein.todo.todo.MainActivity}: java.lang.NullPointerException
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:137)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5041)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:  Caused by: java.lang.NullPointerException
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at com.waiyanhein.todo.todo.MainActivity.onCreate(MainActivity.java:21)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:5104)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.access$600(ActivityThread.java:141) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:137) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5041) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
01-23 12:28:45.945 2972-2972/? E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method) 
01-23 12:28:45.961 2972-2975/? D/dalvikvm: GC_CONCURRENT freed 249K, 13% free 2610K/2988K, paused 2ms+0ms, total 18ms
01-23 12:28:45.961 386-801/? W/ActivityManager:   Force finishing activity com.waiyanhein.todo.todo/.MainActivity
01-23 12:28:46.177 386-801/? D/dalvikvm: GC_FOR_ALLOC freed 1205K, 46% free 8703K/16012K, paused 15ms, total 15ms
01-23 12:28:46.209 386-402/? D/dalvikvm: GC_FOR_ALLOC freed 149K, 40% free 9732K/16012K, paused 19ms, total 19ms
01-23 12:28:46.241 386-402/? D/dalvikvm: GC_FOR_ALLOC freed 6K, 33% free 10832K/16012K, paused 15ms, total 15ms
01-23 12:28:46.241 386-402/? I/dalvikvm-heap: Grow heap (frag case) to 13.126MB for 2536932-byte allocation
01-23 12:28:46.301 386-401/? D/dalvikvm: GC_FOR_ALLOC freed 2K, 29% free 13307K/18492K, paused 59ms, total 59ms
01-23 12:28:46.309 386-389/? D/dalvikvm: GC_CONCURRENT freed <1K, 29% free 13307K/18492K, paused 2ms+1ms, total 10ms

所以我的第一个问题是，当我在活动中自定义操作栏时，为什么会抛出错误？我的代码有什么问题吗？我的第二个问题是如上所述，如何用我自定义的操作栏完全替换操作栏。

Answer 1

NullPointerException正在发生，因为您在设置{{{{}}}之前尝试访问和修改ActionBar Activity上的支持NoActionBar 1}}作为替代品。但是，根据您所需的“选项菜单”行为，您不希望这样做。

如果Toolbar具有Activity实施，其选项菜单将自动创建为ActionBar本身的下拉菜单。由于您使用的是ActionBar主题，因此请勿将NoActionBar设置为支持Toolbar，并且选项菜单将恢复为旧样式。

如何在Android中使用自定义操作栏完全替换AppCompatActivity的操作栏？

1 个答案: