Handler的構造函數:
1、
public Handler() {
this(null, false);
}
2、
public Handler(@Nullable Callback callback) {
this(callback, false);
}
3、
public Handler(@NonNull Looper looper) {
this(looper, null, false);
}
4、
public Handler(@NonNull Looper looper, @Nullable Callback callback) {
this(looper, callback, false);
}
@UnsupportedAppUsage
public Handler(@NonNull Looper looper, @Nullable Callback callback, boolean async) {
mLooper = looper;
mQueue = looper.mQueue;
mCallback = callback;
mAsynchronous = async;
}