popupwindow的源码分析

来源：互联网发布：ubuntu 反应慢编辑：程序博客网时间：2024/06/11 03:27

闲来无事把popupwindow的源码看了一遍，能力有限只看懂了一部分。下面我们来看看源码：

<span style="font-size:14px;">private int mWindowLayoutType = WindowManager.LayoutParams.TYPE_APPLICATION_PANEL;</span>

分析：从这里可以看出来PopupWindow(弹出窗口)实际上是一个子窗口，它是一个独立的类（并不继承于Window）。

<span style="font-size:14px;">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);        final int animStyle = a.getResourceId(R.styleable.PopupWindow_popupAnimationStyle, -1);        mAnimationStyle = animStyle == R.style.Animation_PopupWindow ? -1 : animStyle;        a.recycle();        setBackgroundDrawable(bg);    }</span>

分析：这个一看就很清楚，这是它的构造函数，里面通过context对象获取了windowManager对象和属性typedArray和一些动画style，a.recycle是释放typedArray。里面还有很多构造函数，主要是对它进行一些参数的初始化，比如设置contentView、宽、高、焦点等。详细请看源码。
接下来主要介绍的是我们经常要用到的显示popupwindow位置的几个方法。因为严格来说这个PopuWindow就是用来在指定位置显示一个View的。主要方法有下面：
public void showAsDropDown(View anchor) 
       showAsDropDown(View anchor, int xoff, int yoff)
       showAtLocation(View parent, int gravity, int x, int y) 
下面来看看他们的源码：
public void showAsDropDown(View anchor) {        showAsDropDown(anchor, 0, 0);    } public void showAsDropDown(View anchor, int xoff, int yoff) {        showAsDropDown(anchor, xoff, yoff, DEFAULT_ANCHORED_GRAVITY);    }<pre name="code" class="java">public void showAtLocation(View parent, int gravity, int x, int y) {        showAtLocation(parent.getWindowToken(), gravity, x, y);    }


第一个调用的是第二个方法，所以我们直接分析第二个方法：

public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {        if (isShowing() || mContentView == null) {            return;        }        registerForScrollChanged(anchor, xoff, yoff, gravity);        mIsShowing = true;        mIsDropdown = true;        WindowManager.LayoutParams p = createPopupLayout(anchor.getWindowToken());        preparePopup(p);        updateAboveAnchor(findDropDownPosition(anchor, p, xoff, yoff, gravity));        if (mHeightMode < 0) p.height = mLastHeight = mHeightMode;        if (mWidthMode < 0) p.width = mLastWidth = mWidthMode;        p.windowAnimations = computeAnimationResource();        invokePopup(p);    }
<pre name="code" class="java">public void showAtLocation(IBinder token, int gravity, int x, int y) {        if (isShowing() || mContentView == null) {            return;        }        unregisterForScrollChanged();        mIsShowing = true;        mIsDropdown = false;        WindowManager.LayoutParams p = createPopupLayout(token);        p.windowAnimations = computeAnimationResource();               preparePopup(p);        if (gravity == Gravity.NO_GRAVITY) {            gravity = Gravity.TOP | Gravity.START;        }        p.gravity = gravity;        p.x = x;        p.y = y;        if (mHeightMode < 0) p.height = mLastHeight = mHeightMode;        if (mWidthMode < 0) p.width = mLastWidth = mWidthMode;        invokePopup(p);    }

分析：

先解释下参数：
anchor:就是PopupWindow要显示位置的参照物
xoff: PopupWindow相对于anchor的左下角x轴方向的偏移大小
yoff: PopupWindow相对于anchor的左下角y轴方向的偏移大小

我觉得这两个方法的区别就是showAtLocation能够设置popupwindow显示在参照物view的哪个方位然后设置偏移值，而showAsDropDown则是默认弹出窗显示在参照物view的左下角，然后设置偏移值。代码具体分析：

刚开始isShowing()判断当前PopupWindow是否显示，或者mContentView是否为空，是的话就不用去继续执行下面的代码了。然后unregisterForScrollChanged()，为了滑动改变注册，就是有可能anchor有滑动，或者ContentView过大，有的地方放不开。

private void unregisterForScrollChanged() {        WeakReference<View> anchorRef = mAnchor;        View anchor = null;        if (anchorRef != null) {            anchor = anchorRef.get();        }        if (anchor != null) {            ViewTreeObserver vto = anchor.getViewTreeObserver();            vto.removeOnScrollChangedListener(mOnScrollChangedListener);        }        mAnchor = null;    }
就是注册一下滑动的全局的监听，注册之前先注销一下之前的注册，防止ViewTreeObserver失效。在这里使用了一个弱引用对anchor，防止anchor这个类已经无用了，anchor仍然无法回收内存。接下来为PopupWindow设置显示参数，调用了createPopupLayout(anchor.getWindowToken())

看下这个方法：

private WindowManager.LayoutParams createPopupLayout(IBinder token) {        // generates the layout parameters for the drop down        // we want a fixed size view located at the bottom left of the anchor        WindowManager.LayoutParams p = new WindowManager.LayoutParams();<span style="color:#ff0000;">//<span style="font-family: Simsun; line-height: 24px;">创建一个WindowManager.LayoutParams的实例</span></span>        // these gravity settings put the view at the top left corner of the        // screen. The view is then positioned to the appropriate location        // by setting the x and y offsets to match the anchor's bottom        // left corner        p.gravity = Gravity.START | Gravity.TOP;<span style="color:#ff0000;">//接下来为实例p设置了一系列的参数</span>        p.width = mLastWidth = mWidth;        p.height = mLastHeight = mHeight;        if (mBackground != null) {            p.format = mBackground.getOpacity();        } else {            p.format = PixelFormat.TRANSLUCENT;        }        p.flags = computeFlags(p.flags);        p.type = mWindowLayoutType;        p.token = token;        p.softInputMode = mSoftInputMode;        p.setTitle("PopupWindow:" + Integer.toHexString(hashCode()));        return p;    }

接下来分析方法：invokePopup(p)，它才是真正的把PopupWindow显示在特定的位置上。其实就使用Activity中的WindowManager对象对mPopupView进行了添加显示。

<span style="font-size:14px;">private void invokePopup(WindowManager.LayoutParams p) {        if (mContext != null) {            p.packageName = mContext.getPackageName();        }        mPopupView.setFitsSystemWindows(mLayoutInsetDecor);        setLayoutDirectionFromAnchor();        mWindowManager.addView(mPopupView, p);//<span style="color: rgb(255, 0, 0); font-family: Arial; line-height: 26px;">调用addView完成添加</span>    }</span>

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