android之Fragment的bug解决

最近做一个功能，当第二次进入一个界面的时候出现一个奇怪的bug,如下面详细的log信息：

10-01 13:36:23.549: E/AndroidRuntime(14188): Process: com.android.settings, PID: 14188
10-01 13:36:23.549: E/AndroidRuntime(14188): android.view.InflateException: Binary XML file line #43: Error inflating class fragment
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:713)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at com.android.settings.accessibility.ToggleCaptioningPreferenceFragment.onCreateView(ToggleCaptioningPreferenceFragment.java:69)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.Fragment.performCreateView(Fragment.java:1700)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:890)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.BackStackRecord.run(BackStackRecord.java:698)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.FragmentManagerImpl$1.run(FragmentManager.java:443)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.os.Handler.handleCallback(Handler.java:808)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.os.Handler.dispatchMessage(Handler.java:103)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.os.Looper.loop(Looper.java:193)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.ActivityThread.main(ActivityThread.java:5333)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at java.lang.reflect.Method.invokeNative(Native Method)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at java.lang.reflect.Method.invoke(Method.java:515)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at dalvik.system.NativeStart.main(Native Method)
10-01 13:36:23.549: E/AndroidRuntime(14188): Caused by: java.lang.IllegalArgumentException: Binary XML file line #43: Duplicate id 0x7f0b0034, tag null, or parent id 0xffffffff with another fragment for com.android.settings.accessibility.CaptionPropertiesFragment
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.app.Activity.onCreateView(Activity.java:4912)
10-01 13:36:23.549: E/AndroidRuntime(14188): 	at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)

如上的log信息可以知道：加载了一个（Duplicate）重复的Fragment（CaptionPropertiesFragment）。问题是代码应该是没有问题的！具体看看我系的代码：

public class ToggleCaptioningPreferenceFragment extends Fragment {
    private static final float DEFAULT_FONT_SIZE = 48f;

    private CaptionPropertiesFragment mPropsFragment;
    private SubtitleView mPreviewText;
    private CaptioningManager mCaptioningManager;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mCaptioningManager = (CaptioningManager) getActivity()
                .getSystemService(Context.CAPTIONING_SERVICE);
    }

    @Override
    public View onCreateView(
            LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        final View rootView = inflater.inflate(R.layout.captioning_preview, container, false);

        // We have to do this now because PreferenceFrameLayout looks at it
        // only when the view is added.
        if (container instanceof PreferenceFrameLayout) {
            ((PreferenceFrameLayout.LayoutParams) rootView.getLayoutParams()).removeBorders = true;
        }

        return rootView;
    }

从报错信息可以知道出错的代码：final View rootView = inflater.inflate(R.layout.captioning_preview, container, false);

那么报错信息说是加载了重复的Fragment（CaptionPropertiesFragment）。实际上这个重复的Fragment在这个layout文件里面布局的：R.layout.captioning_preview。

很显然，就是第一次进入这个界面，再退出的时候，这个用过的Fragment（CaptionPropertiesFragment）没有remove掉！从而出现了两个问题：

（1）为什么会出现这个Fragment（CaptionPropertiesFragment）没有remove,

（2）怎么解决这个问题！

在activity中不同的frament之间项目替换的时候，FragmentManager只会remove和add这些frament，然而这些frament里面自己加载的frament（这里就是我们的CaptionPropertiesFragment）是没有被remove. 很显然这是一个缺陷！因为后一个frament（CaptionPropertiesFragment）很明显是依赖与他的父frament的，应该同时递归的remove.

那么如何解决这个问题呢！很显然就是在不用这个frament（ToggleCaptioningPreferenceFragment）的时候把他里面加载的frament给remove掉！这个操作在ToggleCaptioningPreferenceFragment的onDestroyView()里面就可以解决问题了！如下代码：

	@Override
	public void onDestroyView() {
		super.onDestroyView();

	 	if(mPropsFragment != null){
			FragmentManager f = getFragmentManager();
			if(f != null && !f.isDestroyed()){
				final FragmentTransaction ft = f.beginTransaction();
				if(ft != null){
					ft.remove(mPropsFragment).commit();
				}
			}
	 	}
	}

这里要注意f.isDestroyed()这样来判断是否这个FragmentManager处于Destroyed，如果不加这个判断的话，横竖屏切换时候会出错！

注意：对于这个问题，网上有各种无效的解决办法。