所以我在自定义视图中遇到了这个问题。我正在尝试使用无限滚动动画创建自定义RelativeLayout。为实现这一目标，我创建了一个布局backgroundscrollrelativelayout.xml，如下所示：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/mainTile"/>
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/topTile" />
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/leftTile" />
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/diagonalTile" />
</RelativeLayout>
我们的想法是ImageView将在动画更新回调中转换它们的位置。
我已经创建了BackgroundScrollRelativeLayout.java，如此：
public class BackgroundScrollRelativeLayout extends RelativeLayout {
final int layoutToUse = R.layout.backgroundscrollrelativelayout;
final int mainTileId = R.id.mainTile;
final int leftTileId = R.id.leftTile;
final int topTileId = R.id.topTile;
final int diagonalTileId = R.id.diagonalTile;
final float valueStart = 0.0f;
final float valueEnd = 1.0f;
final long animationDuration = 50000L;
private Context mContext;
private ValueAnimator scrollAnimator;
private ImageView mainTile;
private ImageView leftTile;
private ImageView topTile;
private ImageView diagonalTile;
public BackgroundScrollRelativeLayout(Context context) {
super(context);
mContext = context;
acquireViewsInLayout();
initializeAnimator();
scrollAnimator.start();
}
public BackgroundScrollRelativeLayout(Context context, AttributeSet attrs) {
super(context, attrs);
mContext = context;
acquireViewsInLayout();
initializeAnimator();
scrollAnimator.start();
}
public BackgroundScrollRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
mContext = context;
acquireViewsInLayout();
initializeAnimator();
scrollAnimator.start();
}
@Override
public void setBackgroundColor(int color) {
// Not supported
}
@Override
public void setBackgroundResource(int resid) {
// Not supported
}
@Override
public void setBackground(Drawable background) {
mainTile.setBackground(background);
leftTile.setBackground(background);
}
/*
@Override
public void setBackgroundDrawable(Drawable background) {
//super.setBackgroundDrawable(background);
//mainTile.setBackground(background);
//leftTile.setBackground(background);
}*/
// Intent: Inflate the layout associated with this View
private void inflateLayout(){
// TO inflateLayout, we connect the inflater to context, then we call inflate the layout associated
// with this view
//LayoutInflater inflater = LayoutInflater.from(mContext);
//inflater.inflate(layoutToUse, this);
inflate(getContext(), layoutToUse, this);
}
// Intent: Find all Views in Layout
private void findAllViewsById(){
mainTile = (ImageView)this.findViewById(mainTileId);
leftTile = (ImageView)this.findViewById(leftTileId);
topTile = (ImageView)this.findViewById(topTileId);
diagonalTile = (ImageView)this.findViewById(diagonalTileId);
}
// Intent: Concretely acquire all Views in Layout
private void acquireViewsInLayout(){
// TO acquireViewsInLayout, we inflate the layout,
// then we find the view of each known view id and save the view
inflateLayout();
findAllViewsById();
}
// Intent: Initialize animator properties
private void initializeAnimator(){
// TO initializeAnimator, we set how the animator will keep track of animation,
// then we set the animation repeat type, then we set the type of interpolation,
// then we set the animation duration, then we apply animation update listener
scrollAnimator = ValueAnimator.ofFloat(valueStart, valueEnd);
scrollAnimator.setRepeatCount(ValueAnimator.INFINITE);
scrollAnimator.setInterpolator(new LinearInterpolator());
scrollAnimator.setDuration(animationDuration);
addScrollAnimatorUpdateListener();
}
// Intent: Add an update listener to the scroll animator
private void addScrollAnimatorUpdateListener(){
// TO addScrollAnimatorUpdateListener, we add an update listener to scroll animator
scrollAnimator.addUpdateListener( new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
// Do something...
updateScrollAnimation();
}
});
}
private void updateScrollAnimation(){
float progress = (float)scrollAnimator.getAnimatedValue();
float widthOfTile = mainTile.getWidth();
float moveInXAxis = widthOfTile * progress;
mainTile.setTranslationX(moveInXAxis);
leftTile.setTranslationX(moveInXAxis - widthOfTile);
// Ignore the rest for now
topTile.setTranslationY(-1.0f);
diagonalTile.setTranslationX(-1.0f);
diagonalTile.setTranslationY(-1.0f);
}
}
我在活动中使用我的自定义视图：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.martianstudio.adivinaque.AppSettingsActivity">
<com.martianstudio.adivinaque.BackgroundScrollRelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/main_activity_animation_icon" />
</RelativeLayout>
这样做的目的是允许用户使用android:background指定要滚动的背景。我不希望父RelativeLayout将此drawable作为背景。相反，我希望ImageViews将drawable设置为背景。我在自定义视图中覆盖了setBackground，以便只有ImageView将drawable设置为背景而不是RelativeLayout（默认情况下）。
@Override
public void setBackground(Drawable background) {
mainTile.setBackground(background);
leftTile.setBackground(background);
}
然而，我收到此错误：
java.lang.NullPointerException at com.martianstudio.adivinaque.BackgroundScrollRelativeLayout.setBackground
这表示mainTile中的setBackground尚未设置（它为空）。在我的findAllViewsById()中，我明确地写了this.mainTile = (ImageView)this.findViewById(mainTileId);，其中mainTileId = R.id.mainTile，我在inflateLayout()中夸大了布局。这两种方法都在类的构造函数中调用。在我看来，由于某些原因，当我像我一样覆盖ImageView方法时，它找不到mainTile setBackground ID。如果我没有覆盖setBackground方法，我没有得到NullPointerException，但是，它默认为默认的setBackground方法，这是我不想要的。我错过了什么吗？
任何帮助将不胜感激:)。谢谢！