判断当前线程是否主线程？

方法一：

public boolean isMainThread() {
    return Looper.getMainLooper() == Looper.myLooper();
}

方法二：

public boolean isMainThread() {
    return Looper.getMainLooper().getThread() == Thread.currentThread();
}

方法三：

public boolean isMainThread() {
    return Looper.getMainLooper().getThread().getId() == Thread.currentThread().getId();
}

参考