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轻量级控件SnackBar应用&源码分析
前言
SnackBar是Android Support Design Library库支持的一个控件，它在使用的时候经常和CoordinatorLayout一起使用，它是介于Toast和Dialog之间的产物，属于轻量级控件很方便的提供提示和动作反馈，有时候我们需要这样的控件，和Toast一样显示便可以消失，又想这个消息提示上进行用户的反馈。然而写Dialog只能通过点击去取消它，所以SnackBar的出现更加让界面优雅。
Part 1、SnackBar的常规使用
Snackbar snackbar = Snackbar.make(v, R.string.tip, Snackbar.LENGTH_INDEFINITE);
snackbar.setAction(R.string.know, new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(MainActivity.this, "click know", Toast.LENGTH_SHORT).show();
}
});
snackbar.setCallback(new Snackbar.Callback() {
@Override
public void onDismissed(Snackbar snackbar, int event) {
super.onDismissed(snackbar, event);
Toast.makeText(MainActivity.this, "onDismissed", Toast.LENGTH_SHORT).show();
}
@Override
public void onShown(Snackbar snackbar) {
super.onShown(snackbar);
Toast.makeText(MainActivity.this, "onShown", Toast.LENGTH_SHORT).show();
}
});
snackbar.setActionTextColor(Color.GREEN);
snackbar.show();
}效果~
tips:
1、Snackbar.LENGTH_INDEFINITE ： 无穷时间
2、SnackBar不能添加多个Action，当添加多个时，后一个会覆盖前一个
3、如果要监听SnackBar的显示和消失则设置setCallback
Part 2、SnackBar源码分析
SnackBar类make方法
@NonNull
public static Snackbar make(@NonNull View view, @NonNull CharSequence text,
@Duration int duration) {
Snackbar snackbar = new Snackbar(findSuitableParent(view));
snackbar.setText(text);
snackbar.setDuration(duration);
return snackbar;
}构造方法 private Snackbar(ViewGroup parent) {
mTargetParent = parent;
mContext = parent.getContext();
ThemeUtils.checkAppCompatTheme(mContext);
LayoutInflater inflater = LayoutInflater.from(mContext);
mView = (SnackbarLayout) inflater.inflate(
R.layout.design_layout_snackbar, mTargetParent, false);
mAccessibilityManager = (AccessibilityManager)
mContext.getSystemService(Context.ACCESSIBILITY_SERVICE);
}tips:1、这里传入的view是一个锚点，然而在构造方法里面将findSuitableParent（）返回的父类传入构造方法中
2、这里看一下R.layout.design_layout_snackbar.xml
<view xmlns:android="http://schemas.android.com/apk/res/android"
class="android.support.design.widget.Snackbar$SnackbarLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
style="@style/Widget.Design.Snackbar" />这里使用了自定义View，路径为class=“android.support.design.widget.Snackbar&SnackbarLayout”；此为内部类，这里先不分析此类。通过使用inflate方法将此View进行填充，由于最后一个参数为false，所以在SnackBar类肯定会有addView方法将此View添加到parent中
findSuitableParent()方法
private static ViewGroup findSuitableParent(View view) {
ViewGroup fallback = null;
do {
if (view instanceof CoordinatorLayout) {
// We‘ve found a CoordinatorLayout, use it
return (ViewGroup) view;
} else if (view instanceof FrameLayout) {
if (view.getId() == android.R.id.content) {
// If we‘ve hit the decor content view, then we didn‘t find a CoL in the
// hierarchy, so use it.
return (ViewGroup) view;
} else {
// It‘s not the content view but we‘ll use it as our fallback
fallback = (ViewGroup) view;
}
}
if (view != null) {
// Else, we will loop and crawl up the view hierarchy and try to find a parent
final ViewParent parent = view.getParent();
view = parent instanceof View ? (View) parent : null;
}
} while (view != null);
// If we reach here then we didn‘t find a CoL or a suitable content view so we‘ll fallback
return fallback;
}tip:这里为了找到描点的父容器，然而在此方法中使用了while循环将不断的查找父级控件等于CoordinatorLayout或者FrameLayout(也就是DecorView)，并将得到的parent返回。
根据代码，将会执行setAction方法
@NonNull
public Snackbar setAction(CharSequence text, final View.OnClickListener listener) {
final TextView tv = mView.getActionView();
if (TextUtils.isEmpty(text) || listener == null) {
tv.setVisibility(View.GONE);
tv.setOnClickListener(null);
} else {
tv.setVisibility(View.VISIBLE);
tv.setText(text);
tv.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
listener.onClick(view);
// Now dismiss the Snackbar
dispatchDismiss(Callback.DISMISS_EVENT_ACTION);
}
});
}
return this;
}这里只不过是将上面所说的那个自定义View设置内容继续向下执行，为SnackBar的show方法
/**
* Show the {@link Snackbar}.
*/
public void show() {
SnackbarManager.getInstance().show(mDuration, mManagerCallback);
}这里又涉及到了一个新类SnackBarManager，从字面意思可只是一个管理SnackBar的类 public void show(int duration, Callback callback) {
synchronized (mLock) {
if (isCurrentSnackbarLocked(callback)) {//(1)
// 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);
scheduleTimeoutLocked(mCurrentSnackbar);
return;
} else if (isNextSnackbarLocked(callback)) {//(2)
// We‘ll just update the duration
mNextSnackbar.duration = duration;
} else {//(3)
// 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)) {//(4)
// If we currently have a Snackbar, try and cancel it and wait in line
return;
} else {//(5)
// Clear out the current snackbar
mCurrentSnackbar = null;
// Otherwise, just show it now
showNextSnackbarLocked();
}
}
}这里为了分析方便在每个判断都加上了标号
tips:
1、(1)中判断如果是当前SnackBar锁定则先将Handler移除队列中CallBack，然后在添加，这样就避免了等待，请注意这里用到的类是SnackbarRecord而不是SnackBar
2、(2)如果是下一个SnackBar则将Duration更新
ok,show()方法中传入了CallBack对象
interface Callback {
void show();
void dismiss(int event);
}这里也就是这个接口，相应实现接口在哪里呢？这里我们回退到SnackBar的show()方法中传入了mManagerCallback，然而经过查找在SnackBar类中就有相应的实现 final SnackbarManager.Callback mManagerCallback = new SnackbarManager.Callback() {
@Override
public void show() {
sHandler.sendMessage(sHandler.obtainMessage(MSG_SHOW, Snackbar.this));
}
@Override
public void dismiss(int event) {
sHandler.sendMessage(sHandler.obtainMessage(MSG_DISMISS, event, 0, Snackbar.this));
}
};到这里我们应该清楚：SnackBar和SnackBarManager之间通过CallBack来实现通信，而SnackBarManager维护的是Callback类。由于上面添加的是是SnackBarRecord而不是SnackBar，来研究一下
private static class SnackbarRecord {
final WeakReference<Callback> callback;
int duration;
SnackbarRecord(int duration, Callback callback) {
this.callback = new WeakReference<>(callback);
this.duration = duration;
}
boolean isSnackbar(Callback callback) {
return callback != null && this.callback.get() == callback;
}
}tips:只是存放了Callback和duration，这里值得学习是使用了弱引用类型来存储Callback，减少了ANR异常
这里对于SnackBar的流程大致完毕，对于回调类中show和dismiss方法，我们来看一下内部是如何进行处理的呢？
static {
sHandler = new Handler(Looper.getMainLooper(), new Handler.Callback() {
@Override
public boolean handleMessage(Message message) {
switch (message.what) {
case MSG_SHOW:
((Snackbar) message.obj).showView();
return true;
case MSG_DISMISS:
((Snackbar) message.obj).hideView(message.arg1);
return true;
}
return false;
}
});
}showView()方法 final void showView() {
if (mView.getParent() == null) {
final ViewGroup.LayoutParams lp = mView.getLayoutParams();
......
}
mTargetParent.addView(mView);
.......//(2)
}ok,通过SnackBarManager调用Callback接口的show方法将View添加到了Parent中在来看省略号(2)中的代码
mView.setOnAttachStateChangeListener(new SnackbarLayout.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(Callback.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 SnackbarLayout.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();
}
}
});
}tips:view.setOnAttachStateChangeListener() : 监听View视图关联状态发生改变
来看一下animateViewIn()
void animateViewIn() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
ViewCompat.setTranslationY(mView, mView.getHeight());
ViewCompat.animate(mView)
.translationY(0f)
.setInterpolator(FAST_OUT_SLOW_IN_INTERPOLATOR)
.setDuration(ANIMATION_DURATION)
.setListener(new ViewPropertyAnimatorListenerAdapter() {
@Override
public void onAnimationStart(View view) {
mView.animateChildrenIn(ANIMATION_DURATION - ANIMATION_FADE_DURATION,
ANIMATION_FADE_DURATION);
}
@Override
public void onAnimationEnd(View view) {
onViewShown();
}
}).start();
} else {
Animation anim = AnimationUtils.loadAnimation(mView.getContext(),
R.anim.design_snackbar_in);
anim.setInterpolator(FAST_OUT_SLOW_IN_INTERPOLATOR);
anim.setDuration(ANIMATION_DURATION);
anim.setAnimationListener(new Animation.AnimationListener() {
@Override
public void onAnimationEnd(Animation animation) {
onViewShown();
}
@Override
public void onAnimationStart(Animation animation) {}
@Override
public void onAnimationRepeat(Animation animation) {}
});
mView.startAnimation(anim);
}
}这里分为大于3.0和小于3.0,分别使用相应的动画来实现SnackBar显示的动画最后我们来看一下最上面说到的SnackBar所使用的自定义View
/**
* @hide
*/
@RestrictTo(GROUP_ID)
public static class SnackbarLayout extends LinearLayout {继承了LinearLayout，默认情况为线性布局，这里只是添加了TextView和Button控件 // Now inflate our content. We need to do this manually rather than using an <include>
// in the layout since older versions of the Android do not inflate includes with
// the correct Context.
LayoutInflater.from(context).inflate(R.layout.design_layout_snackbar_include, this);这里没有用include是为了兼容低版本，root是this意味将该布局添加到这个View中design_layout_snackbar_include.xml:
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<TextView
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"/>
<Button
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"
style="?attr/borderlessButtonStyle"/>
</merge>至此，SnackBar的源码分析完毕轻量级控件SnackBar应用&源码分析
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