使用viewpager时，某些设备中的按钮不可见

Question

布局底部的两个按钮在某些设备上不可见。

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:id="@+id/framelayout1">

        <android.support.v4.view.ViewPager
            android:layout_width="match_parent"
            android:id="@+id/viewpager1"
            android:layout_height="match_parent"></android.support.v4.view.ViewPager>

        <LinearLayout
            android:la yout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:layout_alignParentBottom="true"
            android:gravity="center">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="20dp"
                android:orientation="horizontal">

                <View
                    android:id="@+id/indicator1"
                    android:layout_width="12dp"
                    android:layout_height="12dp"
                    android:layout_margin="5dp"
                    android:background="@drawable/indicator_bg"></View>

                <View
                    android:id="@+id/indicator2"
                    android:layout_width="12dp"
                    android:layout_height="12dp"
                    android:layout_margin="5dp"
                    android:background="@drawable/indicator_bg"></View>

                <View
                    android:id="@+id/indicator3"
                    android:layout_width="12dp"
                    android:layout_height="12dp"
                    android:layout_margin="5dp"
                    android:background="@drawable/indicator_bg"></View>

                <View
                    android:id="@+id/indicator4"
                    android:layout_width="12dp"
                    android:layout_height="12dp"
                    android:layout_margin="5dp"
                    android:background="@drawable/indicator_bg"></View>

            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="#22000000"
                android:orientation="horizontal">

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:id="@+id/registerButton"
                    android:layout_weight="1"
                    android:background="#22000000"
                    android:textColor="@android:color/white"
                    android:text="REGISTER" />

                <View
                    android:layout_width="1dp"
                    android:layout_height="fill_parent"
                    android:background="#cccc" />

                <Button
                    android:layout_width="wrap_content"
                    android:background="#22000000"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:textColor="@android:color/white"
                    android:id="@+id/signButton"
                    android:text="SIGN IN" />
            </LinearLayout>
        </LinearLayout>
    </RelativeLayout>

使用此布局的FragmentActivity代码是

公共类WelcomePage扩展了FragmentActivity {

private Button signButton, registerButton;
private ViewPager pager;
private View indicator1, indicator2, indicator3, indicator4, indicator5;

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.welcome_main);

    pager = (ViewPager) findViewById(R.id.viewpager1);
    signButton = (Button) findViewById(R.id.signButton);
    registerButton = (Button) findViewById(R.id.registerButton);
    indicator1=(View)findViewById(R.id.indicator1);
    indicator2=(View)findViewById(R.id.indicator2);
    indicator3=(View)findViewById(R.id.indicator3);
    indicator4=(View)findViewById(R.id.indicator4);

    Typeface type1 = Typeface.createFromAsset(getAssets(), "fonts/Dosis/Dosis-Regular.ttf");
    signButton.setTypeface(type1);
    registerButton.setTypeface(type1);

    MyPagerAdapter myAdapter = new MyPagerAdapter(getSupportFragmentManager());
    pager.setAdapter(myAdapter);
    update(0);
    pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int i, float v, int i2) {

        }

        @Override
        public void onPageSelected(int i) {
            update(i);
        }

        @Override
        public void onPageScrollStateChanged(int i) {

        }
    });


    signButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(getApplicationContext(), Login.class);
            startActivity(intent);
            finish();
        }
    });

    registerButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            startActivity(new Intent(WelcomePage.this, Signup.class));
            finish();
        }
    });


}

MyPagerAdapter在哪里扩展FragmentPagerAdapter。有人建议调试这个吗？