android PopupWindow 浅析

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弹出框 PopupWindow是android中的一个控件，可以显示给用户看到。不过，它并不是View的子类，是一个独立的类，没有父类，或者说是继承自Object。

这个类提供了很多构造方法，但是大体是两类，一类是需要传入view的，一类是需要传入Context的。

public PopupWindow(View contentView, int width, int height, boolean focusable) {
        if (contentView != null) {
            mContext = contentView.getContext();
            mWindowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
        }

        setContentView(contentView);
        setWidth(width);
        setHeight(height);
        setFocusable(focusable);
    }

传入View的，最终是调用了上面的方法。这个方法会创建一个WindowManager对象。这个很重要，因为PopupWindow里面控件的展示与隐藏，就是调用wm.addView(),wm.removeView()来完成的。

第二种是需要传入一个Context的。

    public PopupWindow(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        mContext = context;
        mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

        final TypedArray a = context.obtainStyledAttributes(
                attrs, R.styleable.PopupWindow, defStyleAttr, defStyleRes);
        final Drawable bg = a.getDrawable(R.styleable.PopupWindow_popupBackground);
        mElevation = a.getDimension(R.styleable.PopupWindow_popupElevation, 0);
        mOverlapAnchor = a.getBoolean(R.styleable.PopupWindow_overlapAnchor, false);

        // Preserve default behavior from Gingerbread. If the animation is
        // undefined or explicitly specifies the Gingerbread animation style,
        // use a sentinel value.
        if (a.hasValueOrEmpty(R.styleable.PopupWindow_popupAnimationStyle)) {
            final int animStyle = a.getResourceId(R.styleable.PopupWindow_popupAnimationStyle, 0);
            if (animStyle == R.style.Animation_PopupWindow) {
                mAnimationStyle = ANIMATION_STYLE_DEFAULT;
            } else {
                mAnimationStyle = animStyle;
            }
        } else {
            mAnimationStyle = ANIMATION_STYLE_DEFAULT;
        }

        final Transition enterTransition = getTransition(a.getResourceId(
                R.styleable.PopupWindow_popupEnterTransition, 0));
        final Transition exitTransition;
        if (a.hasValueOrEmpty(R.styleable.PopupWindow_popupExitTransition)) {
            exitTransition = getTransition(a.getResourceId(
                    R.styleable.PopupWindow_popupExitTransition, 0));
        } else {
            exitTransition = enterTransition == null ? null : enterTransition.clone();
        }

        a.recycle();

        setEnterTransition(enterTransition);
        setExitTransition(exitTransition);
        setBackgroundDrawable(bg);
    }

里面代码很多，但是不复杂。也是创建一个WindowManager对象。

然后看一下显示的方法。显示也是分两种。

    public void showAtLocation(View parent, int gravity, int x, int y) {
        mParentRootView = new WeakReference<>(parent.getRootView());
        showAtLocation(parent.getWindowToken(), gravity, x, y);
    }
    public void showAtLocation(IBinder token, int gravity, int x, int y) {
        if (isShowing() || mContentView == null) {
            return;
        }

        TransitionManager.endTransitions(mDecorView);

        detachFromAnchor();

        mIsShowing = true;
        mIsDropdown = false;
        mGravity = gravity;

        final WindowManager.LayoutParams p = createPopupLayoutParams(token);
        preparePopup(p);

        p.x = x;
        p.y = y;

        invokePopup(p);
    }

看到这里有两个关键方法：preparePopup() , invokePopup(p);主要看后面一个。

    private void invokePopup(WindowManager.LayoutParams p) {
        if (mContext != null) {
            p.packageName = mContext.getPackageName();
        }

        final PopupDecorView decorView = mDecorView;
        decorView.setFitsSystemWindows(mLayoutInsetDecor);

        setLayoutDirectionFromAnchor();

        mWindowManager.addView(decorView, p); // todo: 显示出来

        if (mEnterTransition != null) {
            decorView.requestEnterTransition(mEnterTransition);
        }
    }

另一种显示，最终也是调用到这里了，就不说了。最后看一下隐藏的方法。

    private void dismissImmediate(View decorView, ViewGroup contentHolder, View contentView) {
        // If this method gets called and the decor view doesn't have a parent,
        // then it was either never added or was already removed. That should
        // never happen, but it's worth checking to avoid potential crashes.
        if (decorView.getParent() != null) {
            mWindowManager.removeViewImmediate(decorView); // todo: 移除显示
        }

        if (contentHolder != null) {
            contentHolder.removeView(contentView);
        }

        // This needs to stay until after all transitions have ended since we
        // need the reference to cancel transitions in preparePopup().
        mDecorView = null;
        mBackgroundView = null;
        mIsTransitioningToDismiss = false;
    }

当然，PopupWindow里面还有很多计算位置，判断显示背景之类的方法。或许还有其他的。但是，创建，显示，隐藏的逻辑就是上面分析的这样。

通过分析可以得出一个粗略的结论，就是PopupWindow是对WindowManager的一次细化封装。

以上~