【Android】PopupWindow中使用Spinner出错

1.问题背景

示例效果.png
　　如图，各位看到该效果时，第一反应是使用什么方式实现呢？相信有一部分童鞋会尝试使用PopupWindow+Spinner的方式来实现该效果，而Spinner控件的SpinnerMode属性默认是dialog样式，展现的显示效果不是很难理想，这时，为了更方便的达到与上图一致的效果，有人会尝试去修改SpinnerMode为dropDown，我所认识的一位童鞋就是这样操作的，就这样。。。在点击Spinner准备弹出下拉列表时，异常出现了。。。

错误日志如下：

FATAL EXCEPTION: main
   Process: com.zihao.spinnerdemo, PID: 28778
   android.view.WindowManager$BadTokenException: Unable to add window -- token android.view.ViewRootImpl$W@263c5a2 is not valid; is your activity running?
       at android.view.ViewRootImpl.setView(ViewRootImpl.java:567)
       at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:310)
       at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)
       at android.widget.PopupWindow.invokePopup(PopupWindow.java:1258)
       at android.widget.PopupWindow.showAsDropDown(PopupWindow.java:1110)
       at android.widget.ListPopupWindow.show(ListPopupWindow.java:658)
       at android.widget.Spinner$DropdownPopup.show(Spinner.java:1223)
       at android.widget.Spinner.performClick(Spinner.java:758)
       at android.support.v7.widget.AppCompatSpinner.performClick(AppCompatSpinner.java:438)
       at android.view.View$PerformClick.run(View.java:21153)
       at android.os.Handler.handleCallback(Handler.java:739)
       at android.os.Handler.dispatchMessage(Handler.java:95)
       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)

产生背景：在PopupWindow中使用Spinner且SpinnerMode="dropDown".

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2.错误原因分析

通过对问题产生背景的描述，我们可以很轻松的定位到问题产生的主要原因——即SpinnerMode为dropDown时引发的该异常（但是在SpinnerMode值为dialog时则会正常弹出下拉列表弹窗），那么SpinnerMode="dialog"与SpinnerMode="dropDown"究竟有什么不同？下面我们来看下Spinner源码，来仔细区分下两者的区别。

• Spinner.java中关于下拉列表显示方式(样式)处理

/**
 * Constructs a new spinner with the given context, the supplied attribute
 * set, default styles, popup mode (one of {@link #MODE_DIALOG} or
 * {@link #MODE_DROPDOWN}), and the theme against which the popup should be
 * inflated.
 *
 * @param context The context against which the view is inflated, which
 *                provides access to the current theme, resources, etc.
 * @param attrs The attributes of the XML tag that is inflating the view.
 * @param defStyleAttr An attribute in the current theme that contains a
 *                     reference to a style resource that supplies default
 *                     values for the view. Can be 0 to not look for
 *                     defaults.
 * @param defStyleRes A resource identifier of a style resource that
 *                    supplies default values for the view, used only if
 *                    defStyleAttr is 0 or can not be found in the theme.
 *                    Can be 0 to not look for defaults. * @param mode Constant describing how the user will select choices from
 *             the spinner.
 * @param popupTheme The theme against which the dialog or dropdown popup
 *                   should be inflated. May be {@code null} to use the
 *                   view theme. If set, this will override any value
 *                   specified by
 *                   {@link android.R.styleable#Spinner_popupTheme}.
 *
 * @see #MODE_DIALOG // SpinnerMode="dialog"
 * @see #MODE_DROPDOWN // SpinnerMode="dropDown"
 */
public Spinner(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes, int mode,
        Theme popupTheme) {
    super(context, attrs, defStyleAttr, defStyleRes);
    final TypedArray a = context.obtainStyledAttributes(
            attrs, R.styleable.Spinner, defStyleAttr, defStyleRes);
    if (popupTheme != null) {
        mPopupContext = new ContextThemeWrapper(context, popupTheme);
    } else {
        final int popupThemeResId = a.getResourceId(R.styleable.Spinner_popupTheme, 0);
        if (popupThemeResId != 0) {
            mPopupContext = new ContextThemeWrapper(context, popupThemeResId);
        } else {
            mPopupContext = context;
        }
    }
    if (mode == MODE_THEME) {
        mode = a.getInt(R.styleable.Spinner_spinnerMode, MODE_DIALOG);
    }
    switch (mode) {
        case MODE_DIALOG: {// 当SpinnerMode为dialog时
            mPopup = new DialogPopup();
            mPopup.setPromptText(a.getString(R.styleable.Spinner_prompt));
            break;
        }
        case MODE_DROPDOWN: {// 当SpinnerMode为dropDown时
            // 在这里新建了一个DropdownPopup用来展示下拉列表的内容，关于DropdownPopup源码请看下一片段
            final DropdownPopup popup = new DropdownPopup(
                    mPopupContext, attrs, defStyleAttr, defStyleRes);
            final TypedArray pa = mPopupContext.obtainStyledAttributes(
                    attrs, R.styleable.Spinner, defStyleAttr, defStyleRes);
            mDropDownWidth = pa.getLayoutDimension(R.styleable.Spinner_dropDownWidth,
                    ViewGroup.LayoutParams.WRAP_CONTENT);
            if (pa.hasValueOrEmpty(R.styleable.Spinner_dropDownSelector)) {
                popup.setListSelector(pa.getDrawable(
                        R.styleable.Spinner_dropDownSelector));
            }
            popup.setBackgroundDrawable(pa.getDrawable(R.styleable.Spinner_popupBackground));
            popup.setPromptText(a.getString(R.styleable.Spinner_prompt));
            pa.recycle();
            mPopup = popup;
            mForwardingListener = new ForwardingListener(this) {
                @Override
                public ShowableListMenu getPopup() {
                    return popup;
                }
                @Override
                public boolean onForwardingStarted() {
                    if (!mPopup.isShowing()) {
                        mPopup.show(getTextDirection(), getTextAlignment());
                    }
                    return true;
                }
            };
            break;
        }
    }
    mGravity = a.getInt(R.styleable.Spinner_gravity, Gravity.CENTER);
    mDisableChildrenWhenDisabled = a.getBoolean(
            R.styleable.Spinner_disableChildrenWhenDisabled, false);
    a.recycle();
    // Base constructor can call setAdapter before we initialize mPopup.
    // Finish setting things up if this happened.
    if (mTempAdapter != null) {
        setAdapter(mTempAdapter);
        mTempAdapter = null;
    }
}

• Spinner.java中DropdownPopup类源码

private class DropdownPopup extends ListPopupWindow implements SpinnerPopup {
    private CharSequence mHintText;
    private ListAdapter mAdapter;
    public DropdownPopup(
            Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        setAnchorView(Spinner.this);
        setModal(true);
        setPromptPosition(POSITION_PROMPT_ABOVE);
        setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView parent, View v, int position, long id) {
                Spinner.this.setSelection(position);
                if (mOnItemClickListener != null) {
                    Spinner.this.performItemClick(v, position, mAdapter.getItemId(position));
                }
                dismiss();
            }
        });
    }
    @Override
    public void setAdapter(ListAdapter adapter) {
        super.setAdapter(adapter);
        mAdapter = adapter;
    }
    public CharSequence getHintText() {
        return mHintText;
    }
    public void setPromptText(CharSequence hintText) {
        // Hint text is ignored for dropdowns, but maintain it here.
        mHintText = hintText;
    }
    void computeContentWidth() {
        final Drawable background = getBackground();
        int hOffset = 0;
        if (background != null) {
            background.getPadding(mTempRect);
            hOffset = isLayoutRtl() ? mTempRect.right : -mTempRect.left;
        } else {
            mTempRect.left = mTempRect.right = 0;
        }
        final int spinnerPaddingLeft = Spinner.this.getPaddingLeft();
        final int spinnerPaddingRight = Spinner.this.getPaddingRight();
        final int spinnerWidth = Spinner.this.getWidth();
        if (mDropDownWidth == WRAP_CONTENT) {
            int contentWidth =  measureContentWidth(
                    (SpinnerAdapter) mAdapter, getBackground());
            final int contentWidthLimit = mContext.getResources()
                    .getDisplayMetrics().widthPixels - mTempRect.left - mTempRect.right;
            if (contentWidth > contentWidthLimit) {
                contentWidth = contentWidthLimit;
            }
            setContentWidth(Math.max(
                   contentWidth, spinnerWidth - spinnerPaddingLeft - spinnerPaddingRight));
        } else if (mDropDownWidth == MATCH_PARENT) {
            setContentWidth(spinnerWidth - spinnerPaddingLeft - spinnerPaddingRight);
        } else {
            setContentWidth(mDropDownWidth);
        }
        if (isLayoutRtl()) {
            hOffset += spinnerWidth - spinnerPaddingRight - getWidth();
        } else {
            hOffset += spinnerPaddingLeft;
        }
        setHorizontalOffset(hOffset);
    }
    public void show(int textDirection, int textAlignment) {
        final boolean wasShowing = isShowing();
        computeContentWidth();
        setInputMethodMode(ListPopupWindow.INPUT_METHOD_NOT_NEEDED);
        super.show();
        final ListView listView = getListView();
        listView.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
        listView.setTextDirection(textDirection);
        listView.setTextAlignment(textAlignment);
        setSelection(Spinner.this.getSelectedItemPosition());
        if (wasShowing) {
            // Skip setting up the layout/dismiss listener below. If we were previously
            // showing it will still stick around.
            return;
        }
        // Make sure we hide if our anchor goes away.
        // TODO: This might be appropriate to push all the way down to PopupWindow,
        // but it may have other side effects to investigate first. (Text editing handles, etc.)
        final ViewTreeObserver vto = getViewTreeObserver();
        if (vto != null) {
            final OnGlobalLayoutListener layoutListener = new OnGlobalLayoutListener() {
                @Override
                public void onGlobalLayout() {
                    if (!Spinner.this.isVisibleToUser()) {
                        dismiss();
                    } else {
                        computeContentWidth();
                        // Use super.show here to update; we don't want to move the selected
                        // position or adjust other things that would be reset otherwise.
                        DropdownPopup.super.show();
                    }
                }
            };
            vto.addOnGlobalLayoutListener(layoutListener);
            setOnDismissListener(new OnDismissListener() {
                @Override
                public void onDismiss() {
                    final ViewTreeObserver vto = getViewTreeObserver();
                    if (vto != null) {
                        vto.removeOnGlobalLayoutListener(layoutListener);
                    }
                }
            });
        }
    }
}

通过对以上源码的分析，我们可以看出，当SpinnerMode为dialog时，Spinner内部选择用一个DialogPopup来显示下拉列表内容；当SpinnerMode为dropDown时，Spinner选择用一个DropdownPopup来显示下拉列表内容——即在两种不同的样式下，Spinner分别选择使用Dialog / PopupWindow来进行内容展示。
　　看到这里，我们会疑惑，为什么PopupWindow中嵌套使用Dialog没问题，而嵌套使用PopupWindow就会出错？关于PopupWindow、Dialog窗口添加机制的不同之处推荐阅读Android 窗口添加机制系列2-Dialog,PopupWindow,Toast。

• PopupWindow
  PopupWindow本身依附的WindowToken实际上是也是Activity所依附的WindowToken，这也就是说PopupWindow与Activity所使用的WindowToken是一致的。
  PopupWindow内部不能再使用PopupWindow是因为它获取不到父PopupWindow的WindowToke，从这里我们也可以分析出，一个视图内部不能嵌套与之平级的视图。
• Dialog
  Dialog在初始化视图时，在获取到Activity的WindowToken后，会重新new一个Window，它与Activity分属于不同的Window。

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3.解决方式

搞明白PopupWindow、Dialog的区别以及与WindowsManager的关系后，我们可以通过以下方式来规避类似问题的发生：

• 将外层PopupWindow换为Activity
• 将外层PopupWindow替换为Dialog
• 修改SpinnerMode为dialog
• 使用自定义组件实现类Spinner效果
• 使用Dialog+PopupWindow

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【拓展阅读】
Android 窗口添加机制系列2-Dialog,PopupWindow,Toast
Spinner SpinnerAPI官方文档翻译
视图加载到窗口的过程分析