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在一个空对象引用上调用'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)'。

android
4

我开始开发一个应用程序，但在DetailActivity.java类中遇到了错误，我无法辨别，请帮帮我。提前致谢。

public class PrayerDetailActivity extends AppCompatActivity {

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

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own detail action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    // Show the Up button in the action bar.
    ActionBar actionBar = getSupportActionBar();
    if (actionBar != null) {
        actionBar.setDisplayHomeAsUpEnabled(true);
    }

    // savedInstanceState is non-null when there is fragment state
    // saved from previous configurations of this activity
    // (e.g. when rotating the screen from portrait to landscape).
    // In this case, the fragment will automatically be re-added
    // to its container so we don't need to manually add it.
    // For more information, see the Fragments API guide at:
    //
    // http://developer.android.com/guide/components/fragments.html
    //
    if (savedInstanceState == null) {
        // Create the detail fragment and add it to the activity
        // using a fragment transaction.
        Bundle arguments = new Bundle();
        arguments.putString(PrayerDetailFragment.ARG_ITEM_ID,
                getIntent().getStringExtra(PrayerDetailFragment.ARG_ITEM_ID));
        PrayerDetailFragment fragment = new PrayerDetailFragment();
        fragment.setArguments(arguments);
        getSupportFragmentManager().beginTransaction()
                .add(R.id.prayer_detail_container, fragment)
                .commit();
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == android.R.id.home) {
        // This ID represents the Home or Up button. In the case of this
        // activity, the Up button is shown. For
        // more details, see the Navigation pattern on Android Design:
        //
        // http://developer.android.com/design/patterns/navigation.html#up-vs-back
        //
        navigateUpTo(new Intent(this, PrayerListActivity.class));
        return true;
    }
    return super.onOptionsItemSelected(item);
}

我的xml文件是

<android.support.design.widget.AppBarLayout
    android:id="@+id/app_bar"
    android:layout_width="match_parent"
    android:layout_height="@dimen/app_bar_height"
    android:fitsSystemWindows="true"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/toolbar_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true"
        app:contentScrim="?attr/colorPrimary"
        app:layout_scrollFlags="scroll|exitUntilCollapsed"
        app:toolbarId="@+id/toolbar">

        <android.support.v7.widget.Toolbar
            android:id="@+id/detail_toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_collapseMode="pin"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

    </android.support.design.widget.CollapsingToolbarLayout>

</android.support.design.widget.AppBarLayout>

<android.support.v4.widget.NestedScrollView
    android:id="@+id/prayer_detail_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior" />

显示的错误是

02-09 23:39:45.711 8201-8220/com.jen.jennings.catholicprayers E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab792700
02-09 23:39:54.364 8201-8220/com.jen.jennings.catholicprayers E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab792700
02-09 23:39:55.868 8201-8201/com.jen.jennings.catholicprayers E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                Process: com.jen.jennings.catholicprayers, PID: 8201


                                              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jen.jennings.catholicprayers/com.jen.jennings.catholicprayers.PrayerDetailActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                            at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                            at android.os.Looper.loop(Looper.java:148)
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                         Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                            at com.jen.jennings.catholicprayers.PrayerDetailActivity.onCreate(PrayerDetailActivity.java:29)
                                                                            at android.app.Activity.performCreate(Activity.java:6237)
                                                                            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                            at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                            at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                            at android.os.Looper.loop(Looper.java:148) 
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                            at java.lang.reflect.Method.invoke(Native Method) 
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

 

请帮助我

如果您解决了问题，请将任何答案标记为正确，否则我会提供一个答案，也许可以帮助您 ;) - Skizo-ozᴉʞS ツ
4个回答
3

你的xml文件中没有声明FloatingActionButton。

而你正在onCreate()方法中尝试使用它。

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);

要么将其从您的活动的onCreate()方法中删除，要么在xml布局中声明它。
看起来我只需要删除那个FloatingActionButton代码。我从一个示例项目开始，我认为我已经从布局中删除了该元素，但没有意识到它与代码相关联。由于我忘记了我已经将其删除，因此有点难以追踪。谢谢！ - Murdeth
0

问题出在这些代码行上：

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        Snackbar.make(view, "Replace with your own detail action", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show();
    }
});

尝试在空对象引用上调用虚拟方法'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)'
由于您的xml中没有出现任何FloatingActionButton，因此如果您将其放置在onCreate中，每当您的Acticity进入onCreate()时，它都会查找此id R.id.fab，并且它是NULL，因为它不存在。
0

主要问题是您的活动无法从xml中找到fab引用

如果您真的想要FloatingActionButton，则在所有视图的末尾和完成协调器视图之前添加以下代码。

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    android:src="@android:drawable/ic_dialog_email" />

否则，您可以从活动中删除FloatingActionButton的代码和对象。

0

很可能是findViewById返回了null。在xml中没有id为“fab”的视图。

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