Question

在我的项目中，我有几个屏幕（片段），我想给片段元素（视图）提供动画。我使用了view pager和viewpager适配器和片段。我面临的主要问题 -

在开始加载2页时就像启动时一样，它正在加载第1页和第2页。如果要刷到第二页，则会自动加载第3页。
我需要显示正在使用Universal tween engine的视图（RelativeLayout）的动画。

代码有问题吗？

这是 MainActivity.java 代码 -

    public class MainActivity extends FragmentActivity {    
    ViewPager viewPager;
    PagerAdapter adapter;
    CirclePageIndicator mIndicator;
    private int mWidthScreen;
    private int mHeightScreen;
    private Bundle bundle;
    private List<Fragment> frgScreens;
    private int selectedtheme;
    private Handler mHandler = new Handler();


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewpager_main); // Get the view from viewpager_main.xml        
        buildargument();        
        initialisePaging(); // Page creating function       
    }

    private void initialisePaging(int theme) {
        viewPager = (ViewPager) findViewById(R.id.pager);       
        frgScreens = new Vector<Fragment>(); // clearing old entries        
        viewPager.setOffscreenPageLimit(0);
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

                //Loading fragment # position

                //Instead of starting animation from onCreate start it from here 
                //Only for the first time (for page 1) this callback will not trigger
            }

            @Override
            public void onPageSelected(int position) {
            }

            @Override
            public void onPageScrollStateChanged(int state) {
            }
        });

        frgScreens = this.basicThemes();
        // Bind result to ViewPagerAdapter
        adapter = new ViewPagerAdapter(this.getSupportFragmentManager(), frgScreens);
        this.viewPager.setAdapter(adapter);
    }

    /*
     * Basic fragments
     */
    private List<Fragment> basicThemes() {
        // declaring fragments Group Basic
        Fragment frgBasic1 = Fragment.instantiate(this, Basic1.class.getName());
        Fragment frgBasic2 = Fragment.instantiate(this, Basic2.class.getName());
        Fragment frgBasic3 = Fragment.instantiate(this, Basic3.class.getName());
        Fragment frgBasic4 = Fragment.instantiate(this, Basic4.class.getName()); 
        Fragment frgBasic5 = Fragment.instantiate(this, Basic5.class.getName()); 

        // Passing arguments
        frgBasic1.setArguments(bundle);
        frgBasic2.setArguments(bundle);
        frgBasic3.setArguments(bundle);
        frgBasic4.setArguments(bundle); 
        frgBasic5.setArguments(bundle);



        // Loading screens into Fragment list
        List<Fragment> frgBasicScreens = new Vector<Fragment>();

        frgBasicScreens.add(frgBasic1);
        frgBasicScreens.add(frgBasic2);
        frgBasicScreens.add(frgBasic3);
        frgBasicScreens.add(frgBasic4); 
        frgBasicScreens.add(frgBasic5);

    return frgBasicScreens;

}

private void getScreenHeightWidhth() {
    DisplayMetrics localDisplayMetrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(localDisplayMetrics);
    this.mWidthScreen = localDisplayMetrics.widthPixels;
    this.mHeightScreen = localDisplayMetrics.heightPixels;
    mHandler.post(
            new DisplayToast(this, "Width Screen:" + mWidthScreen + ". Height Screen: " + mHeightScreen + "."));
}

private void buildargument() {
    this.bundle = new Bundle();
    bundle.putInt("mWidthScreen", this.mWidthScreen);
}   

@Override
protected void onResume() {
    super.onResume();
}

@Override
public void onDestroy() {
    super.onDestroy();
}}

现在 ViewPagerAdapter.java

public class ViewPagerAdapter extends FragmentPagerAdapter {    
private List<Fragment> screens; 

public ViewPagerAdapter(FragmentManager fm, List<Fragment> fragments ) {
    super(fm);      
    this.screens = fragments;       
}

@Override
public Fragment getItem(int pos) {
    // getting the position of the item
    return this.screens.get(pos);       
}

@Override
public int getCount() {
    // Getting the size of screen passed
    return this.screens.size();
}}

skinbase.java 是所有基础知识屏幕上常用的一些共享方法。

public abstract class SkinsBase extends Fragment
{
 protected int mWidthScreen;
 protected int mHeightScreen;
 public int skinHeight;
 public int skinWidth;
 public final int textShadowSize = 2;
 .................
 }

现在 basic1.java

public class Basic1 extends SkinsBase { 
private RelativeLayout mBlueBackground;
private Handler mHandler = new Handler();
private static final String TAG = "Basic1";

public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    if (container == null) {
        return null;
    }       
    mContext = container.getContext();
    View v = inflater.inflate(R.layout.blank_viewpager_item, container, false);
    mLayoutForeground = (RelativeLayout) v.findViewById(R.id.relative);

    mBlueBackground = initshape(getResources().getColor(R.color.transparent_blue_80),this.mWidthScreen, (int) (0.10F * this.mWidthScreen), 0,(int) (0.12F *this.mWidthScreen));     
    this.mLayoutForeground.addView(this.mBlueBackground);   

    Log.e(TAG, "Inside basic 1 ");
    return v;
}



public RelativeLayout initshape(int intColor,int intWidthscreen, int intHeight, int intMerginLeft,int intMerginTop) {
    RelativeLayout localRelativeLayout = new RelativeLayout(this.mContext);             
    localRelativeLayout.setBackgroundColor(intColor);       
    RelativeLayout.LayoutParams localLayoutParams = new RelativeLayout.LayoutParams(intWidthscreen, intHeight);
    localLayoutParams.setMargins(intMerginLeft, intMerginTop, 0, 0);
    localRelativeLayout.setLayoutParams(localLayoutParams);         
    return localRelativeLayout;
}   

public void onResume() {
    super.onResume();
}
@Override
public void onPause() {
    super.onPause();
}}

其他 basic2.java，basic3.java，basic4.java ..... 的方式与 basic1.java

我需要将动画应用于 RelativeLayout 。可能吗？而且我希望在页面加载之前没有动画的开始。如果需要更多信息，请评论。 请不要downvote

由于

Answer 1

view-pager的默认行为是它从当前页面的两侧预加载至少1页。请参阅以下链接

ViewPager.setOffscreenPageLimit(0) doesn't work as expected

所以你能做的就是开始动画onCreate从onPageScrolled回调

开始

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        //Loading fragment # position

        //Instead of starting animation from onCreate start it from here 
        //Only for the first time (for page 1) this callback will not trigger
    }

    @Override
    public void onPageSelected(int position) {
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }
});

请参阅setOffscreenPageLimit

设置应保留在页面两侧的页数   处于空闲状态的视图层次结构中的当前页面。页面超出此范围   在需要时，将从适配器重新创建限制。

这是作为优化提供的。如果您事先知道这个号码   您将需要支持或具有延迟加载机制的页面   放在你的页面上，调整这个设置可以带来好处   感知到的分页动画和交互的平滑性。如果你有   少量页面（3-4），您可以一次保持活动状态，   在新创建的视图子树的布局中花费的时间会减少   用户来回翻页。

您应该保持此限制，特别是如果您的网页很复杂   布局。 此设置默认为1。

Answer 2

在我的每个页面/片段中覆盖setUserVisibleHint()都对我有用。您只需在view.startAnimation(animation)内部调用setUserVisibleHint()。但是，这种方法存在一个问题：

在片段中，setUserVisibleHint()在被调用之前 onCreateView()和onViewCreated。

其含义是，当片段首次启动并在view.startAnimation(animation)中调用setUserVisibleHint()时，视图和动画都将为null，并且应用程序将崩溃。

那您如何解决此问题？

在您的每个页面/片段中，只需声明一个全局布尔值（我们称其为fresh_load），然后使用此布尔值检查是否是第一次加载该片段。这是一个例子：

boolean fresh_load = true;
Animation move;
ImageView car;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_carousel_two, container, false);

    // init move and car variables

    if(fresh_load) {
        car.startAnimation(animation);
        fresh_load = false;
    }

    return view;
}

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);

    if((isVisible() && animation != null) && !fresh_load) {
        car.startAnimation(move);
    }
}

我希望这会有所帮助。快活的编码！

想要在viewpager页面上启动动画，但页面正在预加载

2 个答案: