Android 源码分析 —— 从 Toast 出发

/**
 * Show the view or text notification for a short period of time.  This time
 * could be user-definable.  This is the default.
 * @see #setDuration
 */
public static final int LENGTH_SHORT = 0;

/**
 * Show the view or text notification for a long period of time.  This time
 * could be user-definable.
 * @see #setDuration
 */
public static final int LENGTH_LONG = 1;

private static class TN extends ITransientNotification.Stub {
    ...
    static final long SHORT_DURATION_TIMEOUT = 4000;
    static final long LONG_DURATION_TIMEOUT = 7000; 
    ...

    public void handleShow(IBinder windowToken) {
        ...
        mParams.hideTimeoutMilliseconds = mDuration ==
            Toast.LENGTH_LONG ? LONG_DURATION_TIMEOUT : SHORT_DURATION_TIMEOUT;
        ...
    }
    ...
}

/**
 * ...
 * ...                                        . Therefore, we do hide
 * such windows to prevent them from overlaying other apps.
 *
 * @hide
 */
public long hideTimeoutMilliseconds = -1;

Prevent apps to overlay other apps via toast windows

It was possible for apps to put toast type windows
that overlay other apps which toast winodws aren't
removed after a timeout.

Now for apps targeting SDK greater than N MR1 to add a
toast window one needs to have a special token. The token
is added by the notificatoion manager service only for
the lifetime of the shown toast and is then removed
including all windows associated with this token. This
prevents apps to add arbitrary toast windows.

Since legacy apps may rely on the ability to directly
add toasts we mitigate by allowing these apps to still
add such windows for unlimited duration if this app is
the currently focused one, i.e. the user interacts with
it then it can overlay itself, otherwise we make sure
these toast windows are removed after a timeout like
a toast would be.

We don't allow more that one toast window per UID being
added at a time which prevents 1) legacy apps to put the
same toast after a timeout to go around our new policy
of hiding toasts after a while; 2) modern apps to reuse
the passed token to add more than one window; Note that
the notification manager shows toasts one at a time.

long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;

static final int LONG_DELAY = PhoneWindowManager.TOAST_WINDOW_TIMEOUT;
static final int SHORT_DELAY = 2000; // 2 seconds

/** Amount of time (in milliseconds) a toast window can be shown. */
public static final int TOAST_WINDOW_TIMEOUT = 3500; // 3.5 seconds

...

    /** @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;
    }

...

    /**
     * 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);
    }

...

/**
 * Denotes that the annotated element of integer type, represents
 * a logical type and that its value should be one of the explicitly
 * named constants. If the {@link #flag()} attribute is set to true,
 * multiple constants can be combined.
 * ...
 */

Toast.makeText(this, "Hello", 2);

new Thread(new Runnable() {
    @Override
    public void run() {
        Toast.makeText(MainActivity.this, "Call toast on non-UI thread", Toast.LENGTH_SHORT)
                .show();
    }
}).start();

11-07 13:35:33.980 2020-2035/org.mazhuang.androiduidemos E/AndroidRuntime: FATAL EXCEPTION: Thread-77
    java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
        at android.widget.Toast$TN.<init>(Toast.java:390)
        at android.widget.Toast.<init>(Toast.java:114)
        at android.widget.Toast.makeText(Toast.java:277)
        at android.widget.Toast.makeText(Toast.java:267)
        at org.mazhuang.androiduidemos.MainActivity$1.run(MainActivity.java:27)
        at java.lang.Thread.run(Thread.java:856)

// 我们的代码里调用的 makeText 方法
public static Toast makeText(Context context, CharSequence text, @Duration int duration) {
    return makeText(context, null, text, duration);
}

// 隐藏的 makeText 方法，不能手动调用
public static Toast makeText(@NonNull Context context, @Nullable Looper looper,
        @NonNull CharSequence text, @Duration int duration) {
    Toast result = new Toast(context, looper); // 这里的 looper 为 null
    ...

public Toast(@NonNull Context context, @Nullable Looper looper) {
    mContext = context;
    mTN = new TN(context.getPackageName(), looper); // looper 为 null
    ...
}

// looper = null
TN(String packageName, @Nullable Looper looper) {
    ...
    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()");
        }
    }
    ...
}

new Thread(new Runnable() {
    @Override
    public void run() {
        final int MSG_TOAST = 101;
        final int MSG_QUIT = 102;

        Looper.prepare();

        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {

                switch (msg.what) {
                    case MSG_TOAST:
                        Toast.makeText(MainActivity.this, "Call toast on non-UI thread", Toast.LENGTH_SHORT)
                                .show();
                        sendEmptyMessageDelayed(MSG_QUIT, 4000);
                        return;

                    case MSG_QUIT:
                        Looper.myLooper().quit();
                        return;
                }

                super.handleMessage(msg);
            }
        };

        handler.sendEmptyMessage(MSG_TOAST);

        Looper.loop();
    }
}).start();

view.postDelayed(new Runnable() {
    @Override
    public void run() {
        Toast.makeText(MainActivity.this, "background toast", Toast.LENGTH_SHORT).show();
    }
}, 5000);

/**
 * 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;
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="?android:attr/toastFrameBackground">

    <TextView
        android:id="@android:id/message"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_marginHorizontal="24dp"
        android:layout_marginVertical="15dp"
        android:layout_gravity="center_horizontal"
        android:textAppearance="@style/TextAppearance.Toast"
        android:textColor="@color/primary_text_default_material_light"
        />

</LinearLayout>

/**
 * 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);
}

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) {
        ...
    };
}

/**
 * Show the view for the specified duration.
 */
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
    }
}

@Override
public void enqueueToast(String pkg, ITransientNotification callback, int duration)
{
    ...

    synchronized (mToastQueue) {
        ...
        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;
                             }
                         }
                    }
                }

                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);
        }
    }
}

// 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;
             }
         }
    }
}

@GuardedBy("mToastQueue")
void showNextToastLocked() {
    ToastRecord record = mToastQueue.get(0);
    while (record != null) {
        ...
        try {
            record.callback.show(record.token);
            scheduleTimeoutLocked(record);
            return;
        } catch (RemoteException e) {
            ...
            if (index >= 0) {
                mToastQueue.remove(index);
            }
            ...
        }
    }
}

...

@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);
        }
    }
}

...

@GuardedBy("mToastQueue")
void cancelToastLocked(int index) {
    ToastRecord record = mToastQueue.get(index);
    try {
        record.callback.hide();
    } catch (RemoteException e) {
        ...
    }

    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(); // 继续显示队列里的下一个 Toast
    }
}

...

private final class WorkerHandler extends Handler
{
    ...
    @Override
    public void handleMessage(Message msg)
    {
        switch (msg.what)
        {
            case MESSAGE_TIMEOUT:
                handleTimeout((ToastRecord)msg.obj);
                break;
            ...
        }
    }
}

private static class TN extends ITransientNotification.Stub {
    ...
    TN(String packageName, @Nullable Looper looper) {
        ...
        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();
                        ...
                        break;
                    }
                    ...
                }
            }
        };
    }

    /**
     * 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 handleShow(IBinder windowToken) {
        ...
                mWM.addView(mView, mParams);
        ...
    }

    ...

    public void handleHide() {
        ...
                mWM.removeViewImmediate(mView);
        ...
    }
}