Question

我需要制作一个像图片库一样工作的小应用程序：我应该使用查看分页器，当用户向左或向右滑动时，应该从网址加载图片。我有一个带网址的数组，当用户滑动到新页面时它应该开始加载特定的图像（它不应该在开始时加载所有图像）。例如，如果我在第一页上，我应该看到来自url的第一个图像（数组中的索引0）。当我滑到第二页时，app应该开始从索引1加载图像，如果完成加载，它应该出现在屏幕上。

在运行我的应用程序时，我正在打算

11-06 07:47:43.108 9133-9133/com.example.prem.myapplication E/AndroidRuntime:
 FATAL EXCEPTION: main
                                                                                  Process: com.example.prem.myapplication, PID: 9133
                                                                                  java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean)' on a null object reference
                                                                                      at com.example.prem.myapplication.ImageAdapter.instantiateItem(ImageAdapter.java:42)
                                                                                      at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:943)
                                                                                      at android.support.v4.view.ViewPager.populate(ViewPager.java:1091)
                                                                                      at android.support.v4.view.ViewPager.populate(ViewPager.java:1025)
                                                                                      at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                                                      at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                                                      at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1083)
                                                                                      at android.widget.LinearLayout.onMeasure(LinearLayout.java:615)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                                                      at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                                                      at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                                                      at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                                                      at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                                                      at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                                                      at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
                                                                                      at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
                                                                                      at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                                                      at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2615)
                                                                                      at android.view.View.measure(View.java:17547)
                                                                                      at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015)
                                                                                      at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173)
                                                                                      at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379)
                                                                                      at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
                                                                                      at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
                                                                                      at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
                                                                                      at android.view.Choreographer.doCallbacks(Choreographer.java:580)
                                                                                      at android.view.Choreographer.doFrame(Choreographer.java:550)
                                                                                      at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
                                                                                      at android.os.Handler.handleCallback(Handler.java:739)
                                                                                      at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                      at android.os.Looper.loop(Looper.java:135)
                                                                                      at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                                      at java.lang.reflect.Method.invoke(Native Method)
                                                                                      at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                                                                                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

主要活动

公共类MainActivity扩展了AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
    ArrayList<String> articleList = getArticleData();

    ImageAdapter adapter = new ImageAdapter(this,articleList);
    viewPager.setAdapter(adapter);
}

private ArrayList<String> getArticleData() {
    ArrayList<String> articleList = new ArrayList<String>(Arrays.asList(MyArticleData.articles));


    return articleList;
}

}

MyArticleData for Urls

public class MyArticleData {

    static String[] articles = {

            "https://api.learn2crack.com/android/images/donut.png",
            "https://api.learn2crack.com/android/images/eclair.png",
            "https://api.learn2crack.com/android/images/froyo.png",
            "https://api.learn2crack.com/android/images/ginger.png",
            "https://api.learn2crack.com/android/images/honey.png",
            "https://api.learn2crack.com/android/images/icecream.png",
            "https://api.learn2crack.com/android/images/jellybean.png",
            "https://api.learn2crack.com/android/images/kitkat.png",
            "https://api.learn2crack.com/android/images/lollipop.png",
            "https://api.learn2crack.com/android/images/marshmallow.png",
            "https://api.learn2crack.com/android/images/donut.png",
            "https://api.learn2crack.com/android/images/eclair.png",
            "https://api.learn2crack.com/android/images/froyo.png",
            "https://api.learn2crack.com/android/images/ginger.png",
            "https://api.learn2crack.com/android/images/honey.png",
            "https://api.learn2crack.com/android/images/icecream.png",
            "https://api.learn2crack.com/android/images/jellybean.png",
            "https://api.learn2crack.com/android/images/kitkat.png",
            "https://api.learn2crack.com/android/images/lollipop.png",
            "https://api.learn2crack.com/android/images/marshmallow.png",
            "https://api.learn2crack.com/android/images/donut.png",
            "https://api.learn2crack.com/android/images/eclair.png",
            "https://api.learn2crack.com/android/images/froyo.png",
            "https://api.learn2crack.com/android/images/ginger.png",
            "https://api.learn2crack.com/android/images/honey.png",
            "https://api.learn2crack.com/android/images/icecream.png",
            "https://api.learn2crack.com/android/images/jellybean.png",
            "https://api.learn2crack.com/android/images/kitkat.png",
            "https://api.learn2crack.com/android/images/lollipop.png",
            "https://api.learn2crack.com/android/images/marshmallow.png"
    };
}

ImageAdapter

public class ImageAdapter extends PagerAdapter {
Context context;
ArrayList<String> data = new ArrayList<>();
public LayoutInflater mLayoutInflater;
View imageView;

ImageAdapter(Context context, ArrayList<String> urls) {
    this.context = context;
    this.data = urls;
}
@Override
public int getCount() {
    return 30;
}

@Override
public boolean isViewFromObject(View view, Object object) {
    return view == ((LinearLayout) object);
}
@Override

public Object instantiateItem(ViewGroup container, int position) {
    ImageView
     imageView = (ImageView) mLayoutInflater.inflate(R.layout.pager_item, container, false);

    //ImageView imageView = (ImageView) itemView.findViewById(R.id.imageView);
   // ImageView imageView = new ImageView(context);
   // int padding = context.getResources().getDimensionPixelSize(R.dimen.padding_medium);
   // imageView.setPadding(padding, padding, padding, padding);
   // imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
    //imageView.setImageResource(GalImages[position]);

    Picasso.with(context).load(data.get(position)).into(imageView);
    ((ViewPager) container).addView(imageView, 0);
    return imageView;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    container.removeView((LinearLayout) object);
}

}

activity_main.xml中

<LinearLayout 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"
    tools:context=".MainActivity" >

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

</LinearLayout>

pager_item.xml

<ImageView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/imageView" />

我是android.please帮助的新手感谢

Answer 1

try this



public class MyArticleData {

    static String[] articles = {

            "https://api.learn2crack.com/android/images/donut.png",
            "https://api.learn2crack.com/android/images/eclair.png",
            "https://api.learn2crack.com/android/images/froyo.png",
            "https://api.learn2crack.com/android/images/ginger.png",
            "https://api.learn2crack.com/android/images/honey.png",
            "https://api.learn2crack.com/android/images/icecream.png",
            "https://api.learn2crack.com/android/images/jellybean.png",
            "https://api.learn2crack.com/android/images/kitkat.png",
            "https://api.learn2crack.com/android/images/lollipop.png",
            "https://api.learn2crack.com/android/images/marshmallow.png",
            "https://api.learn2crack.com/android/images/donut.png",
            "https://api.learn2crack.com/android/images/eclair.png",
            "https://api.learn2crack.com/android/images/froyo.png",
            "https://api.learn2crack.com/android/images/ginger.png",
            "https://api.learn2crack.com/android/images/honey.png",
            "https://api.learn2crack.com/android/images/icecream.png",
            "https://api.learn2crack.com/android/images/jellybean.png",
            "https://api.learn2crack.com/android/images/kitkat.png",
            "https://api.learn2crack.com/android/images/lollipop.png",
            "https://api.learn2crack.com/android/images/marshmallow.png",
            "https://api.learn2crack.com/android/images/donut.png",
            "https://api.learn2crack.com/android/images/eclair.png",
            "https://api.learn2crack.com/android/images/froyo.png",
            "https://api.learn2crack.com/android/images/ginger.png",
            "https://api.learn2crack.com/android/images/honey.png",
            "https://api.learn2crack.com/android/images/icecream.png",
            "https://api.learn2crack.com/android/images/jellybean.png",
            "https://api.learn2crack.com/android/images/kitkat.png",
            "https://api.learn2crack.com/android/images/lollipop.png",
            "https://api.learn2crack.com/android/images/marshmallow.png"
    };
}



public class MainActivity extends AppCompatActivity {




    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
        ArrayList<String> articleList = getArticleData();

        ImageAdapter adapter = new ImageAdapter(this,articleList);
        viewPager.setAdapter(adapter);
    }

    private ArrayList<String> getArticleData() {
       ArrayList<String> articleList = new ArrayList<String>(Arrays.asList(MyArticleData.articles));


        return articleList;
    }
}







public class ImageAdapter extends PagerAdapter {
    Context context;
    ArrayList<String> data = new ArrayList<String>;

    ImageAdapter(Context context, ArrayList<String> urls) {
        this.context = context;
        this.data = urls;
    }
    @Override
    public int getCount() {
        return 30;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == ((ImageView) object);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageView imageView = new ImageView(context);
        int padding = context.getResources().getDimensionPixelSize(R.dimen.padding_medium);
        imageView.setPadding(padding, padding, padding, padding);
        imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
        //imageView.setImageResource(GalImages[position]);

        Picasso.with(context).load(data.get(position)).into(imageView);
        ((ViewPager) container).addView(imageView, 0);
        return imageView;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        ((ViewPager) container).removeView((ImageView) object);
    }

}


add this dependency in your build gradle.

compile 'com.squareup.picasso:picasso:2.3.2'

Answer 2

为了从网址加载图片，您需要使用Picasso，这是一款功能强大的Android图像下载和缓存库。 Picasso.with(context).load("https://api.learn2crack.com/android/images/kitkat.png") .into(imageView);

使用viewpager的图像幻灯片

2 个答案: