- Toast,的duration参数可选值中LENGTH_SHORT（值为0，2000ms）, LENGTH_LONG（值为1，3500ms）之一
...
/** @hide */
@IntDef({LENGTH_SHORT, LENGTH_LONG})
@Retention(RetentionPolicy.SOURCE)
public @interface Duration {}
...
/**
* Set how long to show the view for.
* @see #LENGTH_SHORT
* @see #LENGTH_LONG
*/
public void setDuration(@Duration int duration) {
mDuration = duration;
mTN.mDuration = duration;
}
...虽然这样，但是实际传入duration参数不为二者也行，依然是显示2000ms。
long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;- 可以在非 UI 线程里调用 Toast，但是得是一个有 Looper 的线程。
- 应用在后台时可以弹出 Toast。
makeText(Context context, CharSequence text, @Duration int duration)主要是创建Toast对象，设置背景为默认view
/**
* Make a standard toast that just contains a text view.
*
* @param context The context to use. Usually your {@link android.app.Application}
* or {@link android.app.Activity} object.
* @param text The text to show. Can be formatted text.
* @param duration How long to display the message. Either {@link #LENGTH_SHORT} or
* {@link #LENGTH_LONG}
*
*/
public static Toast makeText(Context context, CharSequence text, @Duration int duration) {
return makeText(context, null, text, duration);
}
/**
* Make a standard toast to display using the specified looper.
* If looper is null, Looper.myLooper() is used.
* @hide
*/
public static Toast makeText(@NonNull Context context, @Nullable Looper looper,
@NonNull CharSequence text, @Duration int duration) {
Toast result = new Toast(context, looper);
LayoutInflater inflate = (LayoutInflater)
context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);
TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message);
tv.setText(text);
result.mNextView = v;
result.mDuration = duration;
return result;
}来看看Toast构造函数做了啥
public Toast(Context context) {
this(context, null);
}
/**
* Constructs an empty Toast object. If looper is null, Looper.myLooper() is used.
* @hide
*/
public Toast(@NonNull Context context, @Nullable Looper looper) {
mContext = context;
mTN = new TN(context.getPackageName(), looper);
mTN.mY = context.getResources().getDimensionPixelSize(
com.android.internal.R.dimen.toast_y_offset);
mTN.mGravity = context.getResources().getInteger(
com.android.internal.R.integer.config_toastDefaultGravity);
}主要就是构造了一个 TN 对象，计算了位置。TN创建时候主要是设置layoutParams，looper，和handler。
TN(String packageName, @Nullable Looper looper) {
// XXX This should be changed to use a Dialog, with a Theme.Toast
// defined that sets up the layout params appropriately.
final WindowManager.LayoutParams params = mParams;
params.height = WindowManager.LayoutParams.WRAP_CONTENT;
params.width = WindowManager.LayoutParams.WRAP_CONTENT;
params.format = PixelFormat.TRANSLUCENT;
params.windowAnimations = com.android.internal.R.style.Animation_Toast;
params.type = WindowManager.LayoutParams.TYPE_TOAST;
params.setTitle("Toast");
params.flags = WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
| WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
mPackageName = packageName;
if (looper == null) {
// Use Looper.myLooper() if looper is not specified.
looper = Looper.myLooper();
if (looper == null) {
throw new RuntimeException(
"Can't toast on a thread that has not called Looper.prepare()");
}
}
mHandler = new Handler(looper, null) {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case SHOW: {
IBinder token = (IBinder) msg.obj;
handleShow(token);
break;
}
case HIDE: {
handleHide();
// Don't do this in handleHide() because it is also invoked by
// handleShow()
mNextView = null;
break;
}
case CANCEL: {
handleHide();
// Don't do this in handleHide() because it is also invoked by
// handleShow()
mNextView = null;
try {
getService().cancelToast(mPackageName, TN.this);
} catch (RemoteException e) {
}
break;
}
}
}
};
}接下来来看看show()方法：
public void show() {
if (mNextView == null) {
throw new RuntimeException("setView must have been called");
}
INotificationManager service = getService();
String pkg = mContext.getOpPackageName();
TN tn = mTN;
tn.mNextView = mNextView;
try {
service.enqueueToast(pkg, tn, mDuration);
} catch (RemoteException e) {
// Empty
}
}调用了 INotificationManager 的 enqueueToast 方法，INotificationManager 是一个接口，其实现类在 NotificationManagerService 里，我们来看 enqueueToast 方法的实现：
@Override
public void enqueueToast(String pkg, ITransientNotification callback, int duration)
{
......
synchronized (mToastQueue) {
int callingPid = Binder.getCallingPid();
long callingId = Binder.clearCallingIdentity();
try {
ToastRecord record;
int index;
// All packages aside from the android package can enqueue one toast at a time
if (!isSystemToast) {
index = indexOfToastPackageLocked(pkg);
} else {
index = indexOfToastLocked(pkg, callback);
}
// If the package already has a toast, we update its toast
// in the queue, we don't move it to the end of the queue.
if (index >= 0) {
record = mToastQueue.get(index);
record.update(duration);
record.update(callback);
} else {
Binder token = new Binder();
mWindowManagerInternal.addWindowToken(token, TYPE_TOAST, DEFAULT_DISPLAY);
record = new ToastRecord(callingPid, pkg, callback, duration, token);
mToastQueue.add(record);
index = mToastQueue.size() - 1;
}
keepProcessAliveIfNeededLocked(callingPid);
// If it's at index 0, it's the current toast. It doesn't matter if it's
// new or just been updated. Call back and tell it to show itself.
// If the callback fails, this will remove it from the list, so don't
// assume that it's valid after this.
if (index == 0) {
showNextToastLocked();
}
} finally {
Binder.restoreCallingIdentity(callingId);
}
}
}主要就是使用调用方传来的包名、callback 和 duration 构造一个 ToastRecord，然后添加到 mToastQueue 中。如果在 mToastQueue 中已经存在该包名和 callback 的 Toast，则只更新其 duration。接着来看showNextToastLocked();:
@GuardedBy("mToastQueue")
void showNextToastLocked() {
ToastRecord record = mToastQueue.get(0);
while (record != null) {
if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);
try {
record.callback.show(record.token);
scheduleTimeoutLocked(record);
return;
} catch (RemoteException e) {
......
}
}
}
@GuardedBy("mToastQueue")
void cancelToastLocked(int index) {
ToastRecord record = mToastQueue.get(index);
try {
record.callback.hide();
} catch (RemoteException e) {
Slog.w(TAG, "Object died trying to hide notification " + record.callback
+ " in package " + record.pkg);
// don't worry about this, we're about to remove it from
// the list anyway
}
ToastRecord lastToast = mToastQueue.remove(index);
mWindowManagerInternal.removeWindowToken(lastToast.token, true, DEFAULT_DISPLAY);
keepProcessAliveIfNeededLocked(record.pid);
if (mToastQueue.size() > 0) {
// Show the next one. If the callback fails, this will remove
// it from the list, so don't assume that the list hasn't changed
// after this point.
showNextToastLocked();
}
}
@GuardedBy("mToastQueue")
private void scheduleTimeoutLocked(ToastRecord r)
{
mHandler.removeCallbacksAndMessages(r);
Message m = Message.obtain(mHandler, MESSAGE_TIMEOUT, r);
long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;
mHandler.sendMessageDelayed(m, delay);
}
private void handleTimeout(ToastRecord record)
{
if (DBG) Slog.d(TAG, "Timeout pkg=" + record.pkg + " callback=" + record.callback);
synchronized (mToastQueue) {
int index = indexOfToastLocked(record.pkg, record.callback);
if (index >= 0) {
cancelToastLocked(index);
}
}
}
protected class WorkerHandler extends Handler
{
public WorkerHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg)
{
switch (msg.what)
{
case MESSAGE_TIMEOUT:
handleTimeout((ToastRecord)msg.obj);
......这里混入了其他的方法，一块来分析。showNextToastLocked展示toast之后调用scheduleTimeoutLocked让handler在duration时间之后发一个timeout的message，WorkerHandler接收到这个message调用handleTimeout，handleTimeout间接调用cancelToastLocked取消toast，如果队列里还有toast则取出第一个调用showNextToastLocked展示。可以看到实际上的show和cancel都是通过record.callback.show(record.token);和record.callback.hide();进行的。那么callback是啥呢？它是ITransientNotification类型的变量，ITransientNotification是aidl接口，而TN恰好实现了这个接口的方法，事实上它就是调用的TN方法。
package android.app;
/** @hide */
oneway interface ITransientNotification {
void show(IBinder windowToken);
void hide();
}
private static class TN extends ITransientNotification.Stub {
......
/**
* schedule handleShow into the right thread
*/
@Override
public void show(IBinder windowToken) {
if (localLOGV) Log.v(TAG, "SHOW: " + this);
mHandler.obtainMessage(SHOW, windowToken).sendToTarget();
}
/**
* schedule handleHide into the right thread
*/
@Override
public void hide() {
if (localLOGV) Log.v(TAG, "HIDE: " + this);
mHandler.obtainMessage(HIDE).sendToTarget();
}
public void cancel() {
if (localLOGV) Log.v(TAG, "CANCEL: " + this);
mHandler.obtainMessage(CANCEL).sendToTarget();
}可以看到是通过handler创建一个message后发送出去：
public void sendToTarget() {
target.sendMessage(this);
}注释说的很清楚发送之后，toast在handleShow(token)中展示：
public void handleShow(IBinder windowToken) {
if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView
+ " mNextView=" + mNextView);
// If a cancel/hide is pending - no need to show - at this point
// the window token is already invalid and no need to do any work.
if (mHandler.hasMessages(CANCEL) || mHandler.hasMessages(HIDE)) {
return;
}
if (mView != mNextView) {
// remove the old view if necessary
handleHide();
mView = mNextView;
Context context = mView.getContext().getApplicationContext();
String packageName = mView.getContext().getOpPackageName();
if (context == null) {
context = mView.getContext();
}
mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
// We can resolve the Gravity here by using the Locale for getting
// the layout direction
final Configuration config = mView.getContext().getResources().getConfiguration();
final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection());
mParams.gravity = gravity;
if ((gravity & Gravity.HORIZONTAL_GRAVITY_MASK) == Gravity.FILL_HORIZONTAL) {
mParams.horizontalWeight = 1.0f;
}
if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == Gravity.FILL_VERTICAL) {
mParams.verticalWeight = 1.0f;
}
mParams.x = mX;
mParams.y = mY;
mParams.verticalMargin = mVerticalMargin;
mParams.horizontalMargin = mHorizontalMargin;
mParams.packageName = packageName;
mParams.hideTimeoutMilliseconds = mDuration ==
Toast.LENGTH_LONG ? LONG_DURATION_TIMEOUT : SHORT_DURATION_TIMEOUT;
mParams.token = windowToken;
if (mView.getParent() != null) {
if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
mWM.removeView(mView);
}
if (localLOGV) Log.v(TAG, "ADD! " + mView + " in " + this);
// Since the notification manager service cancels the token right
// after it notifies us to cancel the toast there is an inherent
// race and we may attempt to add a window after the token has been
// invalidated. Let us hedge against that.
try {
mWM.addView(mView, mParams);
trySendAccessibilityEvent();
} catch (WindowManager.BadTokenException e) {
/* ignore */
}
}
}handleShow会先判断handler消息队列里有没有cancel或者hide，有的话直接return。接着通过context.getSystemService(Context.WINDOW_SERVICE);获取到WindowManager实例赋给mWM,这个实例其实是WindowManagerImpl类型的一个对象。然后设置好mParams的各种参数，调用mWM.addView(mView, mParams);展示toast。这里有两点需要注意：
- 实际上调用的是
WindowManagerImpl的addView方法，WindowManagerImpl又通过代理类WindowManagerGlobal的addView方法将toast的view添加到窗口，最终展示。
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow){
......// 参数检查
final WindowManager.LayoutParams wparams =(WindowManager.LayoutParams)params;
/* ① 如果当前窗口需要被添加为另一个窗口的附属窗口（子窗口），则需要让父窗口视自己的情况
对当前窗口的布局参数(LayoutParams)进行一些修改 */
if(parentWindow != null) {
parentWindow.adjustLayoutParamsForSubWindow(wparams);
}
ViewRootImpl root;
ViewpanelParentView = null;
synchronized (mLock) {
......
// WindowManager不允许同一个View被添加两次
int index = findViewLocked(view, false);
if (index >= 0) { throw new IllegalStateException("......");}
// ② 创建一个ViewRootImpl对象并保存在root变量中
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
/* ③ 将作为窗口的控件、布局参数以及新建的ViewRootImpl以相同的索引值保存在三个
数组中。到这步为止，我们可以认为完成了窗口信息的添加工作 */
mViews[index] = view;
mRoots[index] = root;
mParams[index] = wparams;
}
try{
/* ④ 将作为窗口的控件设置给ViewRootImpl。这个动作将导致ViewRootImpl向WMS
添加新的窗口、申请Surface以及托管控件在Surface上的重绘动作。这才是真正意义上
完成了窗口的添加操作*/
root.setView(view, wparams, panelParentView);
}catch (RuntimeException e) { ...... }
}当然，这里再继续挖就到了view树的绘制流程去了，这不是本文的重点。
- 第二个需要注意的是这是Android api 26的源码，和25有所不同：
图片来自drakeet的ToastCompat
也就是说在Android7.1.1上可能会遇到BadTokenException（当然我没遇到）。什么情况会遇到呢？源码上说了，因为the notification manager service会在通知toast取消之后cancel token，所以我们可能会试图在token失效的时候add一个window，这时候就出现了异常。避免方法也就是hook一下WindowManager的addview方法，手动catch这个exception。
到这里我们的分析就差不多结束了。那么有个问题：token是干嘛的？这里token是这个窗口的Binder对象，WMS通过它对窗口进行IPC通信。
参考：