snackbar.setText(text);
snackbar.setDuration(duration);
return snackbar;
}
通过inflate获取到SnackBarContentLayout布局，SnackBarContentLayout实际上是一个LinearLayout，再来看看R.layout.design_layout_snackbar_include：
android:id="@+id/snackbar_text" android:layout_width=“wrap_content” android:layout_height=“wrap_content” android:layout_weight=“1” android:paddingTop="@dimen/design_snackbar_padding_vertical" android:paddingBottom="@dimen/design_snackbar_padding_vertical" android:paddingLeft="@dimen/design_snackbar_padding_horizontal" android:paddingRight="@dimen/design_snackbar_padding_horizontal" android:textAppearance="@style/TextAppearance.Design.Snackbar.Message" android:maxLines="@integer/design_snackbar_text_max_lines" android:layout_gravity=“center_vertical|left|start” android:ellipsize=“end” android:textAlignment=“viewStart”/> android:id="@+id/snackbar_action" android:layout_width=“wrap_content” android:layout_height=“wrap_content” android:layout_marginLeft="@dimen/design_snackbar_extra_spacing_horizontal" android:layout_marginStart="@dimen/design_snackbar_extra_spacing_horizontal" android:layout_gravity=“center_vertical|right|end” android:paddingTop="@dimen/design_snackbar_padding_vertical" android:paddingBottom="@dimen/design_snackbar_padding_vertical" android:paddingLeft="@dimen/design_snackbar_padding_horizontal" android:paddingRight="@dimen/design_snackbar_padding_horizontal" android:visibility=“gone” android:textColor="?attr/colorAccent" /> 没错，这就是Snackbar的主要布局了，一个TextView和一个Button。 获取到的SnackbarContentLayout，通过实例化Snackbar，传进了Snackbar的构造方法中，最后到了Snackbar的父类baseTransientBottomBar的构造方法中： protected baseTransientBottomBar(@NonNull ViewGroup parent, @NonNull View content, @NonNull ContentViewCallback contentViewCallback) { … //省略不重要代码 mTargetParent = parent; //之前findSuitableParent方法找到的ViewGroup //callback传进来的SnackbarContentLayout，其实现了ContentViewCallback接口 mContentViewCallback = contentViewCallback; mContext = parent.getContext(); ThemeUtils.checkAppCompatTheme(mContext); LayoutInflater inflater = LayoutInflater.from(mContext); // Note that for backwards compatibility reasons we inflate a layout that is defined // in the extending Snackbar class. This is to prevent breakage of apps that have custom // coordinator layout behaviors that depend on that layout. mView = (SnackbarbaseLayout) inflater.inflate( R.layout.design_layout_snackbar, mTargetParent, false); mView.addView(content);//将SnackbarContentLayout添加到SnackbarLayout中 …//省略剩余代码 } @NonNull public View getView() { return mView; } 已经备注很详细了，接着来看看R.layout.design_layout_snackbar: class=“android.support.design.widget.Snackbar$SnackbarLayout” android:layout_width=“match_parent” android:layout_height=“wrap_content” android:layout_gravity=“bottom” /> 注意到class了吗，没错，此View是Snackbar中定义的SnackbarLayout，继承自baseTransientBottomBar中的SnackbarbaseLayout，而SnackbarbaseLayout继承自frameLayout。SnackbarLaout中只重新了onMeasure方法，其他实现都在SnackbarbaseLayout中。 还有一个关键的地方，layout_gravity被设置成了bottom，这也是为什么Snackbar总显示在底部的原因。 到这里我们已经知道了**Snackbar的布局实际上是一个frameLayout，其内容是一个LinearLayout。baseTransientBottomBar提供了getView方法来获取mView，mView即为Snackbar的根布局frameLayout。**既然能获取到根布局，那往此布局中addView肯定是没问题了，之前提到的问题3也可以利用这一点解决了。 为什么不是action，而是show。因为我关心的是Snackbar如何显示的。 public void show() { SnackbarManager.getInstance().show(mDuration, mManagerCallback); } 看到这里是不是有点蒙蔽了，怎么到了SnackbarManager的show方法了，不着急，我们先来看看mManagerCallback: final SnackbarManager.Callback mManagerCallback = new SnackbarManager.Callback() { @Override public void show() { sHandler.sendMessage(sHandler.obtainMessage(MSG_SHOW, baseTransientBottomBar.this)); } @Override public void dismiss(int event) { sHandler.sendMessage(sHandler.obtainMessage(MSG_DISMISS, event, 0, baseTransientBottomBar.this)); } }; mManagerCallback内部使用了Handler来控制show和dismiss，最终sHandler会调用showView： final void showView() { if (mView.getParent() == null) { final ViewGroup.LayoutParams lp = mView.getLayoutParams(); if (lp instanceof CoordinatorLayout.LayoutParams) { // 如果LayoutParams是CoordinatorLayout的，就设置Behavior final CoordinatorLayout.LayoutParams clp = (CoordinatorLayout.LayoutParams) lp; final Behavior behavior = new Behavior(); behavior.setStartAlphaSwipeDistance(0.1f); behavior.setEndAlphaSwipeDistance(0.6f); //设置SwipeDismissBehavior，具体作用就是滑动删除view behavior.setSwipeDirection(SwipeDismissBehavior.SWIPE_DIRECTION_START_TO_END); behavior.setListener(new SwipeDismissBehavior.onDismissListener() { @Override public void onDismiss(View view) { view.setVisibility(View.GONE); dispatchDismiss(baseCallback.DISMISS_EVENT_SWIPE); } @Override public void onDragStateChanged(int state) { switch (state) { case SwipeDismissBehavior.STATE_DRAGGING: case SwipeDismissBehavior.STATE_SETTLING: // If the view is being dragged or settling, pause the timeout SnackbarManager.getInstance().pauseTimeout(mManagerCallback); break; case SwipeDismissBehavior.STATE_IDLE: // If the view has been released and is idle, restore the timeout SnackbarManager.getInstance() .restoreTimeoutIfPaused(mManagerCallback); break; } } }); clp.setBehavior(behavior); // Also set the inset edge so that views can dodge the bar correctly clp.insetEdge = Gravity.BOTTOM; } //重点来了，mView被添加到了mTargetParent中，之前向上遍历view获取的ViewGroup mTargetParent.addView(mView); } mView.setonAttachStateChangeListener( new baseTransientBottomBar.onAttachStateChangeListener() { @Override public void onViewAttachedToWindow(View v) {} @Override public void onViewDetachedFromWindow(View v) { if (isShownOrQueued()) { // If we haven’t already been dismissed then this event is coming from a // non-user initiated action. Hence we need to make sure that we callback // and keep our state up to date. We need to post the call since // removeView() will call through to onDetachedFromWindow and thus overflow. sHandler.post(new Runnable() { @Override public void run() { onViewHidden(baseCallback.DISMISS_EVENT_MANUAL); } }); } } }); if (ViewCompat.isLaidOut(mView)) { if (shouldAnimate()) { // If animations are enabled, animate it in animateViewIn(); } else { // Else if anims are disabled just call back now onViewShown(); } } else { // Otherwise, add one of our layout change listeners and show it in when laid out mView.setonLayoutChangeListener(new baseTransientBottomBar.onLayoutChangeListener() { @Override public void onLayoutChange(View view, int left, int top, int right, int bottom) { mView.setonLayoutChangeListener(null); if (shouldAnimate()) { // If animations are enabled, animate it in animateViewIn(); } else { // Else if anims are disabled just call back now onViewShown(); } } }); } } 通过showView中的代码，终于了解到Snackbar是如何显示的。Snackbar被直接添加到mTargetParent中，就是make方法传递进来的View的父CoordinatorLayout或根布局。 根据Snackbar的布局文件我们知道其layout_gravity为bottom，也就是会显示在mTargetParent的底部。那我们是不是只要将一个有固定高度的CoordinatorLayout传递个给Snackbar的make，就可以改变Snackbar的显示位置了？答案是肯定的！ 到这里我们的问题1和问题2都明了了。那问题4应该如何解决呢？ 根据上面的分析，我们知道show方法会调用SnackbarManager的show方法，那我们就来看看SnackBarManager的源码： class SnackbarManager { static final int MSG_TIMEOUT = 0; private static final int SHORT_DURATION_MS = 1500; private static final int LONG_DURATION_MS = 2750; private static SnackbarManager sSnackbarManager; //单例模式 static SnackbarManager getInstance() { if (sSnackbarManager == null) { sSnackbarManager = new SnackbarManager(); } return sSnackbarManager; } private final Object mLock; private final Handler mHandler; //用来存储当前显示Snackbar的duration和Callback private SnackbarRecord mCurrentSnackbar; //用来存储接下来要显示的Snackbar的duration和Callback private SnackbarRecord mNextSnackbar; private SnackbarManager() { mLock = new Object(); mHandler = new Handler(Looper.getMainLooper(), new Handler.Callback() { @Override public boolean handleMessage(Message message) { switch (message.what) { case MSG_TIMEOUT: handleTimeout((SnackbarRecord) message.obj); return true; } return false; } }); } interface Callback { void show(); void dismiss(int event); } public void show(int duration, Callback callback) { synchronized (mLock) { if (isCurrentSnackbarLocked(callback)) { //判断是否是当前显示的Snackbar，更新duration // Means that the callback is already in the queue. We’ll just update the duration mCurrentSnackbar.duration = duration; // If this is the Snackbar currently being shown, call re-schedule it’s // timeout mHandler.removeCallbacksAndMessages(mCurrentSnackbar);//移除Callback，避免内存泄露 scheduleTimeoutLocked(mCurrentSnackbar);//重新关联设置duration和Callback return; } else if (isNextSnackbarLocked(callback)) { //判断是否是接下来要显示的Snackbar，更新duration // We’ll just update the duration mNextSnackbar.duration = duration; } else { // Else, we need to create a new record and queue it mNextSnackbar = new SnackbarRecord(duration, callback); } if (mCurrentSnackbar != null && cancelSnackbarLocked(mCurrentSnackbar, Snackbar.Callback.DISMISS_EVENT_CONSECUTIVE)) { // If we currently have a Snackbar, try and cancel it and wait in line return; } else { // Clear out the current snackbar mCurrentSnackbar = null; // Otherwise, just show it now showNextSnackbarLocked(); } } } public void dismiss(Callback callback, int event) { synchronized (mLock) { if (isCurrentSnackbarLocked(callback)) { cancelSnackbarLocked(mCurrentSnackbar, event); } else if (isNextSnackbarLocked(callback)) { cancelSnackbarLocked(mNextSnackbar, event); } } } public void onDismissed(Callback callback) { synchronized (mLock) { if (isCurrentSnackbarLocked(callback)) { // If the callback is from a Snackbar currently show, remove it and show a new one mCurrentSnackbar = null; if (mNextSnackbar != null) { showNextSnackbarLocked(); } } } } public void onShown(Callback callback) { synchronized (mLock) { if (isCurrentSnackbarLocked(callback)) { scheduleTimeoutLocked(mCurrentSnackbar); } } } public void pauseTimeout(Callback callback) { synchronized (mLock) { if (isCurrentSnackbarLocked(callback) && !mCurrentSnackbar.paused) { mCurrentSnackbar.paused = true; mHandler.removeCallbacksAndMessages(mCurrentSnackbar); } } } public void restoreTimeoutIfPaused(Callback callback) { synchronized (mLock) { if (isCurrentSnackbarLocked(callback) && mCurrentSnackbar.paused) { mCurrentSnackbar.paused = false; scheduleTimeoutLocked(mCurrentSnackbar); } } } public boolean isCurrent(Callback callback) { synchronized (mLock) { return isCurrentSnackbarLocked(callback); } } public boolean isCurrentOrNext(Callback callback) { synchronized (mLock) { return isCurrentSnackbarLocked(callback) || isNextSnackbarLocked(callback); } } private static class SnackbarRecord { final WeakReference callback; int duration; boolean paused; SnackbarRecord(int duration, Callback callback) { this.callback = new WeakReference<>(callback); this.duration = duration; } boolean isSnackbar(Callback callback) { return callback != null && this.callback.get() == callback; } } private void showNextSnackbarLocked() { if (mNextSnackbar != null) { mCurrentSnackbar = mNextSnackbar; mNextSnackbar = null 《Android学习笔记总结+最新移动架构视频+大厂安卓面试真题+项目实战源码讲义》 【docs.qq.com/doc/DSkNLaERkbnFoS0ZF】 完整内容开源分享 ; final Callback callback = mCurrentSnackbar.callback.get(); if (callback != null) { callback.show(); } else { // The callback doesn’t exist any more, clear out the Snackbar mCurrentSnackbar = null;
