Toast实现源码解析

说明

本篇文章用于介绍Android中Toast的实现原理。和简单实现一个自定义的Toast.

Toast实现

一般常用Toast格式为:

Toast.makeText(context,"text.",Toast.LENGTH_LONG).show();

就此，对Toast做一个了解.首先，Toast调用来了一个静态方法makeText(…),具体实现如下:

/**
* 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, int duration) {
Toast result = new Toast(context);

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;
}

这里设置了Toast的三个属性:mNextView、mDuration.mNextView为显示的Toast view，Toast中使用的是系统的一套资源layout，我们其实可以据此替换绘制的View.再看，这里的Toast 对象的生成，代码如下:

public Toast(Context context) {
mContext = context;
mTN = new TN();
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);
}

发现生成一个TN对象，发现其是处理Toast显示的一个服务处理类。再看Toast.show()方法，代码如下:

public void show() {
if (mNextView == null) {
throw new RuntimeException("setView must have been called");
}

INotificationManager service = getService();
String pkg = mContext.getPackageName();
TN tn = mTN;
tn.mNextView = mNextView;

try {
service.enqueueToast(pkg, tn, mDuration);
} catch (RemoteException e) {
// Empty
}
}

通过代码发现，这里通过Binder方式将处理发送给了INotificationManager来处理，INotificationManager.aidl的实现类为com.android.server.NotificationManagerService,在源码中找到enqueueToast(…)实现如下:

@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 = indexOfToastLocked(pkg, callback);
// If it's already in the queue, we update it in place, we don't
// move it to the end of the queue.
if (index >= 0) {
record = mToastQueue.get(index);
record.update(duration);
} else {
// Limit the number of toasts that any given package except the android
// package can enqueue.  Prevents DOS attacks and deals with leaks.
if (!isSystemToast) {
int count = 0;
final int N = mToastQueue.size();
for (int i=0; i<N; i++) {
final ToastRecord r = mToastQueue.get(i);
if (r.pkg.equals(pkg)) {
count++;
if (count >= MAX_PACKAGE_NOTIFICATIONS) {
Slog.e(TAG, "Package has already posted " + count
+ " toasts. Not showing more. Package=" + pkg);
return;
}
}
}
}

record = new ToastRecord(callingPid, pkg, callback, duration);
mToastQueue.add(record);
index = mToastQueue.size() - 1;
keepProcessAliveLocked(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);
}
}
}

如上代码，发现Toast发送的enqueue会被保存在一个List列表中，最后显示操作如下:

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();
scheduleTimeoutLocked(record);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Object died trying to show notification " + record.callback
+ " in package " + record.pkg);
// remove it from the list and let the process die
int index = mToastQueue.indexOf(record);
if (index >= 0) {
mToastQueue.remove(index);
}
keepProcessAliveLocked(record.pid);
if (mToastQueue.size() > 0) {
record = mToastQueue.get(0);
} else {
record = null;
}
}
}
}

其中，scheduleTimeoutLocked(record);控制显示的时间，Toast提供的显示时间有俩个。通过设置Toast的duration类型控制,如下:

static final int LONG_DELAY = 3500; // 3.5 seconds
static final int SHORT_DELAY = 2000; // 2 seconds

处理回调交由Toast中的ITransientNotification.Stub 处理，即TN对象,show方法启动mShow线程，线程执行代码如下:

public void handleShow() {
if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView
+ " mNextView=" + mNextView);
if (mView != mNextView) {
// remove the old view if necessary
handleHide();
mView = mNextView;
Context context = mView.getContext().getApplicationContext();
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;
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);
mWM.addView(mView, mParams);
trySendAccessibilityEvent();
}
}

最后还是通过WindowManager来加载Toast界面。

自定义Toast

自定义Toast就简单了，两种思路：一个是通过自定义toast的view；一个是通过WindowManager来控制加载view实现一个Toast，这个是最终的解决办法.如下，为简单的替换一个view，代码如下:

private void showToast(Context context){
Toast toast=new Toast(context.getApplicationContext());
LayoutInflater inflate = (LayoutInflater)
this.getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = inflate.inflate(R.layout.test, null);
toast.setView(v);
toast.setDuration(Toast.LENGTH_LONG);
toast.show();
}

布局文件代码为:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:padding="5dip"
android:layout_width="wrap_content"
android:layout_height="wrap_content">

<Button
android:text="cancel"
android:background="@drawable/aa"
android:textColor="@android:color/holo_blue_bright"
android:layout_width="150dip"
android:layout_height="50dip" />

</LinearLayout>

背景控制xml为:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<stroke android:width="1dp" android:color="#63a219"></stroke>
<corners android:radius="5dp" />
</shape>

如上，为我对Toast实现的浅显认识，表做记录。

Enjoytoday,EnjoyCoding