[英]Android - Null pointer reference in Relative Layout
I've made a small class to change layout sizes. 我开了一小堂课来更改布局大小。
Here's the class : 这是课程:
import android.app.Activity;
import android.util.DisplayMetrics;
public class LayoutResize extends Activity{
public DisplayMetrics displayMetrics = new DisplayMetrics();
public int width(int sizeX, DisplayMetrics displayMetrics)
{
int screenWidth = displayMetrics.widthPixels * sizeX / 100;
return screenWidth;
}
public int height(int sizeY, DisplayMetrics displayMetrics)
{
int screenHeight = displayMetrics.heightPixels * sizeY / 100;
return screenHeight;
}
}
And I use it this way in my MainActivity
我在
MainActivity
这种方式使用它
public class MainActivity extends AppCompatActivity {
DisplayMetrics displayMetrics = new DisplayMetrics();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
LayoutResize layoutResize = new LayoutResize();
RelativeLayout relativeViewPager =(RelativeLayout) findViewById(R.id.relativeViewPager);
int relativeViewPagerHeight = layoutResize.height(70, displayMetrics);
ViewGroup.LayoutParams viewPagerParams = relativeViewPager.getLayoutParams();
viewPagerParams.height = relativeViewPagerHeight;
relativeViewPager.setLayoutParams(viewPagerParams);
RelativeLayout headerLayout =(RelativeLayout) findViewById(R.id.headerLayout);
int headerLayoutHeight = layoutResize.height(70, displayMetrics);
ViewGroup.LayoutParams headerLayoutParams = headerLayout.getLayoutParams();
headerLayoutParams.height = headerLayoutHeight;
headerLayout.setLayoutParams(headerLayoutParams);
}
It returns Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.widget.RelativeLayout.getLayoutParams()' on a null object reference
. 它返回
Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.widget.RelativeLayout.getLayoutParams()' on a null object reference
。
If I only use it once, for example only : 如果我只使用一次,例如:
RelativeLayout relativeViewPager =(RelativeLayout) findViewById(R.id.relativeViewPager);
int relativeViewPagerHeight = layoutResize.height(70, displayMetrics);
ViewGroup.LayoutParams viewPagerParams = relativeViewPager.getLayoutParams();
viewPagerParams.height = relativeViewPagerHeight;
relativeViewPager.setLayoutParams(viewPagerParams);
It works, but if I use it like the way I've shown which is twice, it throws null object reference.. 它可以工作,但是如果我像显示两次那样使用它,则会抛出空对象引用。
XML of items in ViewPager
ViewPager
中项目的XML
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center" >
<RelativeLayout
android:id="@+id/headerLayout"
android:layout_width="match_parent"
android:layout_height="fill_parent" >
<ImageView
android:id="@+id/slidingBackground"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true" />
<RelativeLayout
android:id="@+id/headerText"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/titleText"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/messageText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:layout_below="@+id/titleText" />
</RelativeLayout>
</RelativeLayout>
<RelativeLayout
android:id="@+id/slidingImageWrapper"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@+id/headerLayout">
<ImageView
android:id="@+id/slidingImage"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</RelativeLayout>
</RelativeLayout>
Here's the XML for the main class itself 这是主类本身的XML
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<RelativeLayout
android:id="@+id/relativeViewPager"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentTop="true"
android:fillViewport="true"
android:measureAllChildren="false"
android:scrollbars="none" >
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentTop="true" />
</RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:layout_below="@+id/relativeViewPager">
<com.viewpagerindicator.CirclePageIndicator
android:id="@+id/indicator"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:gravity="bottom"
android:padding="10dip"
app:centered="true"
app:fillColor="#ff0099"
app:pageColor="#FF0000"
app:snap="false" />
<Button
android:id="@+id/loginButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Login"
android:textColor="#ffffff"
android:layout_alignParentBottom="true"
android:layout_marginLeft="10dp"
android:layout_marginBottom="10dp"
android:background="@drawable/login_button" />
<Button
android:id="@+id/signUpButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Signup"
android:textColor="#ffffff"
android:layout_alignTop="@+id/loginButton"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_marginRight="63dp"
android:layout_marginEnd="63dp"
android:background="@drawable/signup_button" />
</RelativeLayout>
</RelativeLayout>
I did a stupid mistake of not inflating the view I use (I use another xml which I forgot to inflate) 我犯了一个愚蠢的错误,即没有夸大我使用的视图(我使用了另一个我忘了夸大的xml)
Had to add : 必须添加:
LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View pagerItemInflater = (View) inflater.inflate(R.layout.viewpager_item, null);
And use it like this : 并像这样使用它:
RelativeLayout headerLayout = (RelativeLayout) pagerItemInflater.findViewById(R.id.headerLayout);
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