Android fragment 生命周期

我正在计划一个 Messenger 应用程序，它包含几个区域:

登录/注册
联系人列表
对话
在线状态选择(在线、离开、免打扰...)
设置

在智能手机上，一次应该只有一个 Activity ，但平板电脑应该有一个带快捷方式的侧边栏(在对话 View 中显示联系人列表，在设置中显示设置类别列表)。

据我所知，这些区域将是 fragment ，它们被插入到一个或多个 Activity 中。

所以我开始创建一个具有以下布局 (res/main.xml) 的 Activity :

<?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="match_parent"
    android:orientation="vertical" >

    <fragment
        android:id="@id/main_fragment_focus"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

以及相应的平板电脑布局:(layout-large-land/main.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="match_parent"
    android:orientation="horizontal" >

        <fragment
            android:id="@id/main_fragment_sidebar"
            android:layout_width="@dimen/main_sidebar_width"
            android:layout_height="match_parent" />

            <fragment
        android:id="@id/main_fragment_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

到目前为止，还不错。至少就我的想法而言。所以我创建了一个简单的 Activity ；我正在使用 ActionBarSherlock，因为我想提供与 API 级别 5+ 的兼容性:

package com.pm.messenger;

import android.os.Bundle;
import android.support.v4.app.FragmentManager;
import android.util.Log;

import com.actionbarsherlock.app.SherlockFragmentActivity;

public class PMMessengerActivity extends SherlockFragmentActivity {

    // -------------------------------------------------------------------------

    FragmentManager fragmentManager = null;

    // -------------------------------------------------------------------------

    public void onCreate(Bundle savedInstanceState) {

        // ---------------------------------------------------------------------

        super.onCreate(savedInstanceState);

        // ---------------------------------------------------------------------

        fragmentManager = getSupportFragmentManager();

        // ---------------------------------------------------------------------

        if (savedInstanceState == null) {

            // -----------------------------------------------------------------



            // -----------------------------------------------------------------

        }
        else {

            // -----------------------------------------------------------------



            // -----------------------------------------------------------------

        }

        // ---------------------------------------------------------------------

        Log.d(getClass().getSimpleName(), "no problem before setContentView");

        setContentView(R.layout.main);

        Log.d(getClass().getSimpleName(), "no problem after setContentView");

        // ---------------------------------------------------------------------

    }

    // -------------------------------------------------------------------------

}

执行此操作后，我的应用程序立即崩溃。一开始我想，这是因为我没有提供任何 FragmentManager-FragmentTransactions，但后来我注意到(在插入 Log.d-Lines 之后)调用 SetContentView 时发生了崩溃。

LogCat 输出:

01-24 16:58:26.728: I/ActivityManager(667): START {act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.pm.messenger/.pmMessengerActivity bnds=[912,542][1008,638]} from pid 877
01-24 16:58:26.748: D/dalvikvm(26431): Late-enabling CheckJNI
01-24 16:58:26.758: I/ActivityManager(667): Start proc com.pm.messenger for activity com.pm.messenger/.pmMessengerActivity: pid=26431 uid=10009 gids={3003, 1015}
01-24 16:58:26.778: E/jdwp(26431): Failed sending reply to debugger: Broken pipe
01-24 16:58:26.778: D/dalvikvm(26431): Debugger has detached; object registry had 1 entries
01-24 16:58:26.788: D/OpenGLRenderer(877): Flushing caches (mode 1)
01-24 16:58:26.828: D/pmMessengerActivity(26431): no problem before setContentView
01-24 16:58:26.858: D/AndroidRuntime(26431): Shutting down VM
01-24 16:58:26.858: W/dalvikvm(26431): threadid=1: thread exiting with uncaught exception (group=0x40a3e1f8)
01-24 16:58:26.868: D/OpenGLRenderer(877): Flushing caches (mode 0)
01-24 16:58:26.868: E/AndroidRuntime(26431): FATAL EXCEPTION: main
01-24 16:58:26.868: E/AndroidRuntime(26431): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pm.messenger/com.pm.messenger.pmMessengerActivity}: android.view.InflateException: Binary XML file line #7: Error     inflating class fragment
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.os.Looper.loop(Looper.java:137)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.ActivityThread.main(ActivityThread.java:4424)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at java.lang.reflect.Method.invokeNative(Native Method)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at java.lang.reflect.Method.invoke(Method.java:511)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at dalvik.system.NativeStart.main(Native Method)
01-24 16:58:26.868: E/AndroidRuntime(26431): Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:697)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.view.LayoutInflater.rInflate(LayoutInflater.java:739)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:251)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at com.actionbarsherlock.internal.ActionBarSherlockNative.setContentView(ActionBarSherlockNative.java:119)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at com.actionbarsherlock.app.SherlockFragmentActivity.setContentView(SherlockFragmentActivity.java:262)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at com.pm.messenger.pmMessengerActivity.onCreate(pmMessengerActivity.java:48)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.Activity.performCreate(Activity.java:4465)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-24 16:58:26.868: E/AndroidRuntime(26431):    ... 11 more
01-24 16:58:26.868: E/AndroidRuntime(26431): Caused by: java.lang.NullPointerException: name == null
01-24 16:58:26.868: E/AndroidRuntime(26431):    at java.lang.VMClassLoader.findLoadedClass(Native Method)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:354)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at java.lang.ClassLoader.loadClass(ClassLoader.java:491)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at java.lang.ClassLoader.loadClass(ClassLoader.java:461)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.support.v4.app.Fragment.instantiate(Fragment.java:381)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.support.v4.app.Fragment.instantiate(Fragment.java:359)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:262)
01-24 16:58:26.868: E/AndroidRuntime(26431):    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:669)
01-24 16:58:26.868: E/AndroidRuntime(26431):    ... 22 more
01-24 16:58:26.868: W/ActivityManager(667):   Force finishing activity com.pm.messenger/.pmMessengerActivity
01-24 16:58:27.408: W/ActivityManager(667): Activity pause timeout for ActivityRecord{410d8c98 com.pm.messenger/.pmMessengerActivity}

现在我想，这次崩溃是因为我没有在 XML 中静态提供任何 fragment 类，但是我不想使用它，我想以动态方式实现它.

当我必须在 XML 中静态提供类时，我认为我还需要多个 Activitiy(如 LoginActivity、SignupActivity、ContactListActivity、ConversationActivity)但是...停止，这不对，因为那样我的 fragment 就会失去它们存在的权利恕我直言。

就我的理解而言， fragment 是我的应用程序的一个独立部分，它实现了一个功能区域，就像当天的 Activity 所做的那样；这些将被嵌入到管理后台堆栈的容器 Activity 中。

那么我的逻辑错在哪里呢？我应该使用带有 FrameView 的布局而不是 fragment 吗？不知道。

此外，我没有找到任何好的、易于理解的、有据可查的动态 fragment 管理资源。

最佳答案

你的具体错误是由于你试图膨胀一个不存在的 fragment ，显然。对于动态 fragment ，您应该在静态布局中放置一个 FrameLayout，并在运行时将 fragment 放入这些框架中。下面是一个布局示例:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<View
    android:id="@+id/anchor"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_centerInParent="true" />

<FrameLayout
    android:id="@+id/top_left"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_above="@+id/anchor"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_toLeftOf="@+id/anchor">

</FrameLayout>

<FrameLayout
    android:id="@+id/top_right"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_above="@+id/anchor"
    android:layout_alignParentRight="true"
    android:layout_alignParentTop="true"
    android:layout_toRightOf="@+id/anchor">

</FrameLayout>

<FrameLayout
    android:id="@+id/bottom_left"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/anchor"
    android:layout_toLeftOf="@+id/anchor">

</FrameLayout>

<FrameLayout
    android:id="@+id/bottom_right"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_alignParentBottom="true"
    android:layout_alignParentRight="true"
    android:layout_below="@+id/anchor"
    android:layout_toRightOf="@+id/anchor">

</FrameLayout>

</RelativeLayout>

这恰好将四个大小相等的FrameLayouts放在一个网格中。您可以在运行时添加 fragment :

    Fragment levelsF = Fragment.instantiate(this, 
LevelsFragment.class.getName());
    Fragment waveF = Fragment.instantiate(this,
WaveFragment.class.getName());
    Fragment lightF = Fragment.instantiate(this,    
LightPlayerFragment.class.getName());
    Fragment keyboardF = Fragment.instantiate(this,
KBFragment.class.getName());

    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.add(R.id.top_left, levelsF);
    ft.add(R.id.top_right, waveF);
    ft.add(R.id.bottom_left, lightF);
    ft.add(R.id.bottom_right, keyboardF);     
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    ft.commit();
    getSupportFragmentManager().executePendingTransactions();

如果您不想要静态 fragment ，则根本不要在 xml 中引用它们。

关于Android fragment 生命周期，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14505655/

Android fragment 生命周期

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