之前开发遇到过一个问题:

在一个继承自PreferenceActivity的类上绑定了PreferenceScreen界面,并添加了ActionBar实现返回效果.
在其界面里面还嵌套了新的PreferenceScreen,但是通过嵌套PreferenceScreen实现的二级页面却没有ActionBar.

然后就开始看PreferenceScreen的源码并在网上查找相关信息,后来还是手动为二级嵌套的PreferenceScreen添加了ActionBar并设置其点击事件.
系统的action_bar里面的左上角返回按钮竟然没有id,不得不遍历子控件找出类型为imageButton的控件,再添加click事件...

鉴于这是一个通用问题,便把这个逻辑提到了工具类里,方便其他界面使用.代码如下:

   /**
     * PreferenceScreen use a dialog to display the screen.Here add a clickListener for actionBar's
     * imageButton in the upper left corner in this screen. It will trigger the method dialog.onBackPressed()
     * to dismiss the dialog when user clicked.
     *
     * @param context
     * @param preferenceScreen
     */
    public static void initializeActionBar(Context context, PreferenceScreen preferenceScreen) {
        if (preferenceScreen == null) {
            return;
        }
        Dialog dialog = preferenceScreen.getDialog();
        ImageButton imageButton = null;
        if (dialog == null) {
            return;
        }

        dialog.getActionBar().setDisplayHomeAsUpEnabled(true);
        Window win = dialog.getWindow();
        View mDecorView = win.getDecorView();
        ViewGroup sceneRoot = (ViewGroup) mDecorView.findViewById(getInternalId(context, "action_bar"));
        if (sceneRoot == null) {
            return;
        }

        for (int i = 0; i < sceneRoot.getChildCount(); i++) {
            if (sceneRoot.getChildAt(i) instanceof ImageButton) {
                imageButton = (ImageButton) sceneRoot.getChildAt(i);
                break;
            }
        }
        if (imageButton == null) {
            return;
        }

        imageButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                dialog.onBackPressed();
            }
        });
    }
    
    public static int getInternalId(Context context, String idName) {
        Resources resources = context.getResources();
        int id = resources.getIdentifier(idName, "id", "android");
        return id;
    }

然而测试总有各种各样的办法找出问题,操作是这样的:

在这个二级界面点home返回主界面后,去设置里更改下语言,然后再切回二级界面,发现点击左上角的actionbar返回按钮不管用了.

虽然不常见,但确实需要解决.然后还是得看PreferenceScreen源码,找出出现问题的原因.

原来是切换语言后,view进行了重新绘制,但是PreferenceScreen只是保存了UI基本的结构.里面的mDialog是新建的,不再是老的了.那么之前携带的click事件也不存在了,也就没有了点击返回效果.

下面看看相关源码(源码本就不多,以下几乎是全部逻辑了)

public final class PreferenceScreen extends PreferenceGroup implements AdapterView.OnItemClickListener,
        DialogInterface.OnDismissListener {
    private Dialog mDialog;
    private ListView mListView;
    
    @Override
    protected void onClick() {
        if (getIntent() != null || getFragment() != null || getPreferenceCount() == 0) {
            return;
        }
        
        showDialog(null);
    }
    
    private void showDialog(Bundle state) {
        Context context = getContext();
        if (mListView != null) {
            mListView.setAdapter(null);
        }

        LayoutInflater inflater = (LayoutInflater)
                context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View childPrefScreen = inflater.inflate(
                com.android.internal.R.layout.preference_list_fragment, null);
        mListView = (ListView) childPrefScreen.findViewById(android.R.id.list);
        bind(mListView);

        // Set the title bar if title is available, else no title bar
        final CharSequence title = getTitle();

        // 这里新建了dialog
        Dialog dialog = mDialog = new Dialog(context, context.getThemeResId());
        if (TextUtils.isEmpty(title)) {
            dialog.getWindow().requestFeature(Window.FEATURE_NO_TITLE);
        } else {
            dialog.setTitle(title);
        }
        dialog.setContentView(childPrefScreen);
        dialog.setOnDismissListener(this);
        if (state != null) {
            //初始化的时候state是空的,执行onRestoreInstanceState时才会走这里
            //state不为空,所以重新绘制后会保留之前添加的UI部分
            dialog.onRestoreInstanceState(state);
        }

        // Add the screen to the list of preferences screens opened as dialogs
        getPreferenceManager().addPreferencesScreen(dialog);
        
        dialog.show();
    }
    
    public void onDismiss(DialogInterface dialog) {
        mDialog = null;
        getPreferenceManager().removePreferencesScreen(dialog);
    }

    @Override
    protected Parcelable onSaveInstanceState() {
        final Parcelable superState = super.onSaveInstanceState();
        final Dialog dialog = mDialog;
        if (dialog == null || !dialog.isShowing()) {
            return superState;
        }
        
        //退出前保存UI逻辑
        final SavedState myState = new SavedState(superState);
        myState.isDialogShowing = true;
        myState.dialogBundle = dialog.onSaveInstanceState();
        return myState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (state == null || !state.getClass().equals(SavedState.class)) {
            // Didn't save state for us in onSaveInstanceState
            super.onRestoreInstanceState(state);
            return;
        }
         
        SavedState myState = (SavedState) state;
        super.onRestoreInstanceState(myState.getSuperState());
        if (myState.isDialogShowing) {
            //由于之前有actionbar,所以会将保存的状态传到是哦我Dialog里面
            showDialog(myState.dialogBundle);
        }
    }
    
    private static class SavedState extends BaseSavedState {
        boolean isDialogShowing;
        Bundle dialogBundle;
        
        public SavedState(Parcel source) {
            super(source);
            isDialogShowing = source.readInt() == 1;
            dialogBundle = source.readBundle();
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            dest.writeInt(isDialogShowing ? 1 : 0);
            dest.writeBundle(dialogBundle);
        }

        public SavedState(Parcelable superState) {
            super(superState);
        }

        public static final Parcelable.Creator<SavedState> CREATOR =
                new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }
}
 

从源码看,我们需要在新的mDialog里重新加一次点击事件,正好可以加在调用原生onRestoreInstanceState方法之后.

    @Override
    protected void onRestoreInstanceState(Bundle state) {
        super.onRestoreInstanceState(state);
         initializeActionBar(...);
    }