从 Activity 调用 Fragment 方法答案

【问题标题】：Call Fragment method from Activity从 Activity 调用 Fragment 方法
【发布时间】：2014-06-15 12:03:01
【问题描述】：

我需要在 onResume 活动中调用片段内的方法，但总是显示 FC 并出现此错误：

06-15 14:59:58.496: E/AndroidRuntime(28904): FATAL EXCEPTION: main
06-15 14:59:58.496: E/AndroidRuntime(28904): Process: com.carlosdiaz.tfm_usuarios, PID: 28904
06-15 14:59:58.496: E/AndroidRuntime(28904): java.lang.RuntimeException: Unable to resume activity {com.carlosdiaz.tfm_usuarios/com.carlosdiaz.tfm_usuarios.Grupos}: java.lang.NullPointerException
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2774)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2803)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2238)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.os.Handler.dispatchMessage(Handler.java:102)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.os.Looper.loop(Looper.java:136)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread.main(ActivityThread.java:5001)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at java.lang.reflect.Method.invokeNative(Native Method)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at java.lang.reflect.Method.invoke(Method.java:515)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at dalvik.system.NativeStart.main(Native Method)
06-15 14:59:58.496: E/AndroidRuntime(28904): Caused by: java.lang.NullPointerException
06-15 14:59:58.496: E/AndroidRuntime(28904):    at com.carlosdiaz.tfm_usuarios.Grupos.onResume(Grupos.java:52)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.Activity.performResume(Activity.java:5310)
06-15 14:59:58.496: E/AndroidRuntime(28904):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2764)
06-15 14:59:58.496: E/AndroidRuntime(28904):    ... 12 more

我不知道我能做什么。

这是 mi OnCreate 和 onResume 方法：

public class Grupos extends Activity {

    PlaceholderFragment fragment;

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

        fragment = (PlaceholderFragment) getFragmentManager().findFragmentById(R.layout.fragment_grupos);

        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    protected void onResume()
    {
        super.onResume();
        Log.i("Test","Test");
        fragment.myOnResume();
    }

...

我的方法在 Fragment 类中：

public static class PlaceholderFragment extends Fragment {
...
public void myOnResume() {
            GruposTask getGrupos = new GruposTask(PlaceholderFragment.this, getActivity());
            getGrupos.execute(id);
        }
...

提前谢谢你！

编辑：

现在我尝试在活动 xml 中创建片段，以便以后通过 oncreate() 以这种方式调用它：

PlaceholderFragment mainFragment = (PlaceholderFragment)getFragmentManager().findFragmentById(R.id.listGroup);

这是活动布局：

   xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.carlosdiaz.tfm_usuarios.Grupos"
    tools:ignore="MergeRootFrame">
    <fragment class="com.carlosdiaz.tfm_usuarios.Grupos.PlaceholderFragment"
            android:id="@+id/listGroup"
            android:layout_weight="1"
            android:layout_width="0dp"
            android:layout_height="match_parent" />
 </FrameLayout>

但现在我遇到了这个错误：

06-15 19:20:15.956: E/AndroidRuntime(7424): FATAL EXCEPTION: main
06-15 19:20:15.956: E/AndroidRuntime(7424): Process: com.carlosdiaz.tfm_usuarios, PID: 7424
06-15 19:20:15.956: E/AndroidRuntime(7424): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.carlosdiaz.tfm_usuarios/com.carlosdiaz.tfm_usuarios.Grupos}: android.view.InflateException: Binary XML file line #8: Error inflating class fragment
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.os.Looper.loop(Looper.java:136)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.ActivityThread.main(ActivityThread.java:5001)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at java.lang.reflect.Method.invokeNative(Native Method)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at java.lang.reflect.Method.invoke(Method.java:515)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at dalvik.system.NativeStart.main(Native Method)
06-15 19:20:15.956: E/AndroidRuntime(7424): Caused by: android.view.InflateException: Binary XML file line #8: Error inflating class fragment
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:713)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:290)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Activity.setContentView(Activity.java:1929)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at com.carlosdiaz.tfm_usuarios.Grupos.onCreate(Grupos.java:39)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Activity.performCreate(Activity.java:5231)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
06-15 19:20:15.956: E/AndroidRuntime(7424):     ... 11 more
06-15 19:20:15.956: E/AndroidRuntime(7424): Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment com.carlosdiaz.tfm_usuarios.Grupos.PlaceholderFragment: make sure class name exists, is public, and has an empty constructor that is public
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Fragment.instantiate(Fragment.java:597)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Fragment.instantiate(Fragment.java:561)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Activity.onCreateView(Activity.java:4778)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)
06-15 19:20:15.956: E/AndroidRuntime(7424):     ... 21 more
06-15 19:20:15.956: E/AndroidRuntime(7424): Caused by: java.lang.ClassNotFoundException: Didn't find class "com.carlosdiaz.tfm_usuarios.Grupos.PlaceholderFragment" on path: DexPathList[[zip file "/data/app/com.carlosdiaz.tfm_usuarios-2.apk"],nativeLibraryDirectories=[/data/app-lib/com.carlosdiaz.tfm_usuarios-2, /vendor/lib, /system/lib]]
06-15 19:20:15.956: E/AndroidRuntime(7424):     at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
06-15 19:20:15.956: E/AndroidRuntime(7424):     at android.app.Fragment.instantiate(Fragment.java:583)
06-15 19:20:15.956: E/AndroidRuntime(7424):     ... 24 more

【问题讨论】：

请添加logCat。
更新了完整的错误日志
看起来你的fragment 找不到所以它是空的？！

标签： java android android-fragments onresume

【解决方案1】：

那是因为你的订单错了。

PlaceholderFragment fragment;

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

    if(savedInstanceState == null)
    {
        fragment = new PlaceHolderFragment();
        fragment.setTag(R.id.myfragmentId);
        getFragmentManager().beginTransaction()
            .add(R.id.container, fragment).commit();
    }
    else
    {
        if(fragment == null)
        {
            fragment = (PlaceholderFragment) getFragmentManager().findFragmentByTag(R.id.myfragmentId);
        }
    }
}

【讨论】：

我不这么认为，因为它继续给出空指针错误。另外，我在 Android 片段页面中看到，我必须放 R.id.fragmentId，而不是 R.layout
我现在的问题是我在运行时有一个 ForcedClose，因为布局中的片段没有找到片段的类名，我不知道为什么
更改您的软件包名称，使其中没有下划线。另外，请确保 PlaceholderFragment 实际上在它自己的类中，而不是作为内部静态类在 MainActivity 中。
是的，这就是问题所在。我在活动中有我的片段类，显然是静态的。现在，我用片段代码创建了一个新类，它可以工作了。非常感谢您 ;）。问候！！
如何设置片段ID或标签？

【解决方案2】：

如果您的活动不是父母，您可以使用此代码：

final PlaceholderFragment pf = new PlaceholderFragment();
pf.your_method_name();

这段代码对我有用

【讨论】：

【解决方案3】：

我认为您可以尝试 FragmentActivity，就像 - public class Grupos extends FragmentActivity 因为要使用基于支持的 Fragment 和 Loader API 的活动的基类。 (android.support.v4.app.FragmentActivity)

【讨论】：

好的兄弟@carlosdiazp在我的邮件中给我你的项目：bappy392@gmail.com我什么时候有空然后我解决你的问题......

【解决方案4】：

尝试使用 FragmentActivity 而不是 Activity。

那么你应该调用 getSupportFragmentManager 而不是 getFragmentManager

您也不能将布局传递给 findFragmentById 方法。你应该给它一个片段ID（R.id.FRAGMENT_ID）。

试着像这样：

public class Grupos extends FragmentActivity {

PlaceholderFragment fragment;

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

    fragment = new PlaceholderFragment();
    getSupportFragmentManager().beginTransaction()
                .add(R.id.container, fragment).commit();
}

@Override
protected void onResume()
{
    super.onResume();
    Log.i("Test","Test");
    fragment.myOnResume();
}

【讨论】：

现在我试图给我的片段一个 ID。为此，我在我的活动中创建了一个片段标签（如下所示：<fragment android:name="com.carlosdiaz.tfm_usuarios.Grupos.PlaceholderFragment" android:id="@+id/listGroup" ...）。但是，错误显示06-15 16:30:59.296: E/AndroidRuntime(24797): Caused by: java.lang.ClassNotFoundException: Didn't find class "com.carlosdiaz.tfm_usuarios.Grupos.PlaceholderFragment" on path: DexPathList[[zip file "/data/app/com.carlosdiaz.tfm_usuarios-1.apk"],nativeLibraryDirectories=[/data/app-lib/com.carlosdiaz.tfm_usuarios-1, /vendor/lib, /system/lib]]