我正在尝试Android Java编程。我正在尝试编写自定义（垂直滑动）ViewPager。多亏了StackOverflow，我开始有了一些代码。但是问题在于该应用程序显示空白屏幕（无构建错误）。
我不确定我是否已正确自定义代码。也许我缺少一些非常基本的东西。任何帮助，将不胜感激。预先感谢。
这是我代码的相关部分：
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<mypackagename.VerticalViewPager
android:id="@+id/verticalViewPager"
android:name="verticalViewPager"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"/>
</LinearLayout>
</mypackagename.VerticalViewPager>
</LinearLayout>
MainActivity.java
package mypackagename;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
VerticalViewPager verticalViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
verticalViewPager = (VerticalViewPager) findViewById(R.id.verticalViewPager);
verticalViewPager.setAdapter(new VerticalPagerAdapter(this));
}
}
VerticalViewPager.java
package mypackagename;
import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import androidx.annotation.NonNull;
import androidx.viewpager.widget.ViewPager;
public class VerticalViewPager extends ViewPager {
public VerticalViewPager(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
private void init() {
// The majority of the magic happens here
setPageTransformer(true, new VerticalPageTransformer());
// The easiest way to get rid of the overscroll drawing that happens on the left and right
setOverScrollMode(OVER_SCROLL_NEVER);
}
private static class VerticalPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.75f;
@Override
public void transformPage(@NonNull View page, float position) {
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
page.setAlpha(0);
} else if (position <= 0) { // [-1,0]
// Use the default slide transition when moving to the left page
page.setAlpha(1);
// Counteract the default slide transition
page.setTranslationX(page.getWidth() * -position);
//set Y position to swipe in from top
float yPosition = position * page.getHeight();
page.setTranslationY(yPosition);
page.setScaleX(1);
page.setScaleY(1);
} else if (position <= 1) { // [0,1]
page.setAlpha(1);
// Counteract the default slide transition
page.setTranslationX(page.getWidth() * -position);
// Scale the page down (between MIN_SCALE and 1)
float scaleFactor = MIN_SCALE
+ (1 - MIN_SCALE) * (1 - Math.abs(position));
page.setScaleX(scaleFactor);
page.setScaleY(scaleFactor);
} else { // (1,+Infinity]
// This page is way off-screen to the right.
page.setAlpha(0);
}
}
}
/**
* Swaps the X and Y coordinates of your touch event.
*/
private MotionEvent swapXY(MotionEvent ev) {
float width = getWidth();
float height = getHeight();
float newX = (ev.getY() / height) * width;
float newY = (ev.getX() / width) * height;
ev.setLocation(newX, newY);
return ev;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev){
boolean intercepted = super.onInterceptTouchEvent(swapXY(ev));
swapXY(ev); // return touch coordinates to original reference frame for any child views
return intercepted;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
return super.onTouchEvent(swapXY(ev));
}
}
VerticalPagerAdapter.java
package mypackagename;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.viewpager.widget.PagerAdapter;
public class VerticalPagerAdapter extends PagerAdapter {
private String[] mResources = {"To start off lets understand what exactly Android CardView is? Its a new widget for Android, which can be used to display a card sort of a layout in android. As you may know Android material design is inspired from paper and ink concept. Mostly it displays views on top of each other, with shadows. In simple terms, Android CardView is such a view which has all material design properties, most importantly showing shadows according the elevation. The best part about this view is that it extends FrameLayout and it can be displayed on all the platforms of android since it’s available through the Support v7 library. Lets have a look at some of its properties:","To start off lets understand what exactly Android CardView is? Its a new widget for Android, which can be used to display a card sort of a layout in android. As you may know Android material design is inspired from paper and ink concept. Mostly it displays views on top of each other, with shadows. In simple terms, Android CardView is such a view which has all material design properties, most importantly showing shadows according the elevation. The best part about this view is that it extends FrameLayout and it can be displayed on all the platforms of android since it’s available through the Support v7 library. Lets have a look at some of its properties:"};
private LayoutInflater mLayoutInflater;
VerticalPagerAdapter(Context context) {
mLayoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount() {
return mResources.length;
}
@Override
public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
return view == ((LinearLayout) object);
}
@NonNull
@Override
public Object instantiateItem(@NonNull ViewGroup container, int position) {
View itemView = mLayoutInflater.inflate(R.layout.activity_main, container, false);
TextView label = (TextView) itemView.findViewById(R.id.textView);
label.setText(mResources[position]);
container.addView(itemView);
return itemView;
}
@Override
public void destroyItem(ViewGroup container, int position, @NonNull Object object) {
container.removeView((LinearLayout) object);
}
}