相关疑难解决方法(0)

我正在开始一个使用AppCompat/ActionBarCompatin v7支持库的新项目.我试图找出如何getSupportActionBar在片段中使用from.我承载片段的活动扩展了ActionBarActivity,但我没有看到片段的类似支持类.

从我的片段中

    public class CrimeFragment extends Fragment {
          //...

          getActivity().getSupportActionBar().setSubtitle(R.string.subtitle); // getSupportActionBar is not defined in the v4 version of Fragment

          //...
    }

使用它的谷歌页面(http://android-developers.blogspot.in/2013/08/actionbarcompat-and-io-2013-app-source.html)表示v4片段应该没有变化.我是否需要将所有getActivity()电话投入ActionBarActivity？这似乎是糟糕的设计.

使用Android Studio菜单选项Refactor - > Refactor to Androidx迁移到Androidx软件包后...

我收到以下错误:

Error inflating class androidx.constraintlayout.widget.ConstraintLayout

我在运行时得到这个nullPointerException:

引起:java.lang.NullPointerException:尝试在空对象引用上调用虚方法'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)'

mainActivity中的代码:

package com.example.vasilis.spangreek;

import android.app.ActionBar;
import android.app.Activity;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.util.DisplayMetrics;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ExpandableListView;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import adapter.ExpandableListViewAdapter;
import model.NavDrawerItem;


public class MainActivity extends Activity {

    private DrawerLayout mDrawerLayout;
    private ExpandableListView mExpandableListView;
    private ActionBarDrawerToggle mActionBarDrawerToggle;

    //nav drawer Title
    private CharSequence mDrawerTitle;

    //used to store app titles
    private CharSequence mTitles;

    //slide menu items
    private String[] navMenuItems;
    private …

我正在研究当前Android应用程序中优秀的Mapbox库.

我试图整合这个问题时遇到过这个问题PlacePickerActivity.

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.hide()' on a null object reference
        at com.mapbox.mapboxsdk.plugins.places.picker.ui.PlacePickerActivity.onCreate(PlacePickerActivity.java:65)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)

我的应用程序风格如下: -

<resources>
    <style name="AppTheme" parent="Theme.AppCompat.DayNight.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

</resources>

我使用的版本是: -

// MAPBOX
implementation "com.mapbox.mapboxsdk:mapbox-android-sdk:$mapBoxSdkVersion"
implementation "com.mapbox.mapboxsdk:mapbox-android-plugin-traffic:$mapBoxTrafficVersion"
implementation "com.mapbox.mapboxsdk:mapbox-android-plugin-places:$mapBoxPlacesVersion"

    mapBoxSdkVersion = "6.8.1"
    mapBoxTrafficVersion = "0.6.0"
    mapBoxPlacesVersion = "0.6.0"

我配置我的工具栏如下: -

   /**
     * @param toolbar
     */
    private void manageToolbar(final Toolbar toolbar) {
        mToolbar …