Android Studios FATAL EXCEPTION：主要是java.lang.RuntimeException

时间：2016-06-09 08:24:19

标签： java android android-fragments android-studio android-toolbar

我是Android工作室的新手，我有大约一到两周的教程，虽然大多数教程已经过时我仍然试图学习Android工作室。第一次在stackoverflow上问一个问题，无论如何我一直在尝试创建一个具有片段导航抽屉的应用程序。我一直在使用这个教程https://guides.codepath.com/android/Fragment-Navigation-Drawer。 我已经开始使用“制作状态栏半透明”部分，但在我开始使用该部分之前，我被建议运行我的应用程序，它失败并给了我一个大错误。此外，我不知道如何扩展片段，如教程所述。

这是我在logcat中的错误：

   06-09 00:35:01.708 988-988/com.example.drago_000.fragmentnavigationdrawer E/AndroidRuntime: FATAL EXCEPTION: main 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.drago_000.fragmentnavigationdrawer/com.example.drago_000.fragmentnavigationdrawer.MainActivity}: java.lang.NullPointerException

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.drago_000.fragmentnavigationdrawer.MainActivity.onPostCreate(MainActivity.java:113)
at android.app.Instrumentation.callActivityOnPostCreate(Instrumentation.java:1142)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2042)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
at android.app.ActivityThread.access$600(ActivityThread.java:130) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4745) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
at dalvik.system.NativeStart.main(Native Method) 

这是我的MainActivity.java 

package com.example.drago_000.fragmentnavigationdrawer;

import android.content.res.Configuration;
import android.support.design.widget.NavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;


public class MainActivity extends AppCompatActivity{
    private DrawerLayout mDrawer;
    private Toolbar toolbar;
    private NavigationView nvDrawer;
    private ActionBarDrawerToggle drawerToggle;
    private ActionBarDrawerToggle setupDrawerToggle() {
        return new ActionBarDrawerToggle(this, mDrawer, toolbar, R.string.drawer_open,  R.string.drawer_close);
    }



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Set a Toolbar to replace the ActionBar.
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        // Find our drawer view
        mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        nvDrawer = (NavigationView) findViewById(R.id.nvView);
        // Setup drawer view
        setupDrawerContent(nvDrawer);

        // Tie DrawerLayout events to the ActionBarToggle
        mDrawer.addDrawerListener(drawerToggle);
    }




    private void setupDrawerContent(NavigationView navigationView) {
        navigationView.setNavigationItemSelectedListener(
                new NavigationView.OnNavigationItemSelectedListener() {
                    @Override
                    public boolean onNavigationItemSelected(MenuItem menuItem) {
                        selectDrawerItem(menuItem);
                        return true;
                    }
                });
    }

    public void selectDrawerItem(MenuItem menuItem) {
        // Create a new fragment and specify the fragment to show based on nav item clicked
        Fragment fragment = null;
        Class fragmentClass;
        switch(menuItem.getItemId()) {
            case R.id.nav_first_fragment:
                fragmentClass = FirstFragment.class;
                break;
            case R.id.nav_second_fragment:
                fragmentClass = SecondFragment.class;
                break;
            case R.id.nav_third_fragment:
                fragmentClass = ThirdFragment.class;
                break;
            default:
                fragmentClass = FirstFragment.class;
        }

        try {
            fragment = (Fragment) fragmentClass.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }

        // Insert the fragment by replacing any existing fragment
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();

        // Highlight the selected item has been done by NavigationView
        menuItem.setChecked(true);
        // Set action bar title
        setTitle(menuItem.getTitle());
        // Close the navigation drawer
        mDrawer.closeDrawers();
    }



    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (drawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    // `onPostCreate` called when activity start-up is complete after `onStart()`
    // NOTE! Make sure to override the method with only a single `Bundle` argument
    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        drawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggles
        drawerToggle.onConfigurationChanged(newConfig);
    }}

FirstFragment.java 

package com.example.drago_000.fragmentnavigationdrawer;

/**
 * Created by drago_000 on 6/9/2016.
 */
public class FirstFragment {
}

SecondFragment.java 

package com.example.drago_000.fragmentnavigationdrawer;

/**
 * Created by drago_000 on 6/9/2016.
 */
public class SecondFragment {
}

ThirdFragment.java 

package com.example.drago_000.fragmentnavigationdrawer;

/**
 * Created by drago_000 on 6/9/2016.
 */
public class ThirdFragment {
}

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.drago_000.fragmentnavigationdrawer.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />


    <!-- This DrawerLayout has two children at the root  -->
<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"
    app:headerLayout="@layout/nav_header"
    />
</android.support.v4.widget.DrawerLayout>

</RelativeLayout>

nav_header.xml 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="192dp"
    android:background="?attr/colorPrimaryDark"
    android:padding="16dp"
    android:theme="@style/ThemeOverlay.AppCompat.Dark"
    android:orientation="vertical"
    android:gravity="bottom">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Header"
        android:textColor="@android:color/white"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1"/>

</LinearLayout>

toolbar.xml 

<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>

drawer_view.xml 

<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <group android:checkableBehavior="single">
        <item
            android:id="@+id/nav_first_fragment"
            android:icon="@drawable/ic_one"
            android:title="First" />
        <item
            android:id="@+id/nav_second_fragment"
            android:icon="@drawable/ic_two"
            android:title="Second" />
        <item
            android:id="@+id/nav_third_fragment"
            android:icon="@drawable/ic_three"
            android:title="Third" />
    </group>

</menu>

/res/values/v16/styles.xml 

<resources>
    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="android:windowTranslucentStatus">true</item>
    </style>
</resources>

/res/values/string.xml 

<resources>
    <string name="app_name">FragmentNavigationDrawer</string>
    <string name="drawer_open">Open navigation drawer</string>
    <string name="drawer_close">Close navigation drawer</string>

</resources>

的AndroidManifest.xml 

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.drago_000.fragmentnavigationdrawer">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

任何帮助将不胜感激！我在很长一段时间内构建应用程序时遇到了麻烦！此代码基于本教程，直至制作状态栏半透明部分https://guides.codepath.com/android/Fragment-Navigation-Drawer

1 个答案:

答案 0 :(得分：0)

您的drawerToggle为null。在onCreate（）中添加以下行：

mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout);

就在这一行之后：

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