在图库视图中更改选定视图的背景颜色

Question

我想更改所选视图的背景颜色，但在输入以下代码后出现错误。

当用户选择画廊的其他视图时，以前的视图变为默认颜色，但现在出现以下错误

当我在图库视图中更改所选项目时出现错误

gallery.setOnItemSelectedListener(new OnItemSelectedListener() {

        @SuppressLint("ResourceAsColor")
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            // if(position != save)
            // parent.getChildAt(position).setBackgroundResource(R.drawable.state_selected);

            view.setBackgroundColor(Color.GREEN);
            if (save != -1) {
                parent.getChildAt(save).setBackgroundColor(Color.RED);
            }

            save = position;

        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
            // TODO Auto-generated method stub

        }

    });

日志

java.lang.NullPointerException
    at com.example.csglobal.MainActivity$2.onItemSelected(MainActivity.java:119)
    at android.widget.AdapterView.fireOnSelected(AdapterView.java:892)
    at android.widget.AdapterView.selectionChanged(AdapterView.java:879)
    at android.widget.Gallery.selectionChanged(Gallery.java:546)
    at android.widget.AdapterView.checkSelectionChanged(AdapterView.java:1043)
    at android.widget.Gallery.setSelectionToCenterChild(Gallery.java:592)
    at android.widget.Gallery.trackMotionScroll(Gallery.java:396)
    at android.widget.Gallery$FlingRunnable.run(Gallery.java:1504)
    at android.os.Handler.handleCallback(Handler.java:615)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4745)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)

Answer 1

对我来说很好用，试试这个：-

MainActivity.java:-

公共类 MainActivity 扩展 Activity {

            int save = -1;

Integer[] imageIDs = { R.drawable.pic1, R.drawable.pic2, R.drawable.pic3,
                    R.drawable.pic4, R.drawable.pic5, R.drawable.pic6, R.drawable.pic7 };

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

                // Note that Gallery view is deprecated in Android 4.1---
                Gallery gallery = (Gallery) findViewById(R.id.gallery1);
                gallery.setAdapter(new ImageAdapter(this));     

                gallery.setOnItemSelectedListener(new OnItemSelectedListener() {

                    @Override
                    public void onItemSelected(AdapterView<?> parent, View view,
                            int position, long id) {
                        // TODO Auto-generated method stub
                        view.setBackgroundColor(Color.GREEN);

                        if (save != -1) {
                            parent.getChildAt(save).setBackgroundColor(Color.RED);
                        }

                        save = position;
                    }
                    @Override
                    public void onNothingSelected(AdapterView<?> parent) {
                        // TODO Auto-generated method stub

                    }

                });
            }

公共类 ImageAdapter 扩展 BaseAdapter {

私有上下文上下文； 私有 int 项目背景；

  public ImageAdapter(Context c) {
                    context = c;
                    // sets a grey background; wraps around the images
                    TypedArray a = obtainStyledAttributes(R.styleable.MyGallery);
                    itemBackground = a.getResourceId(
                            R.styleable.MyGallery_android_galleryItemBackground, 0);
                    a.recycle();
                }

                // returns the number of images
                public int getCount() {
                    return imageIDs.length;
                }

                // returns the ID of an item
                public Object getItem(int position) {
                    return position;
                }

                // returns the ID of an item
                public long getItemId(int position) {
                    return position;
                }

                // returns an ImageView view
                public View getView(int position, View convertView, ViewGroup parent) {
                    ImageView imageView = new ImageView(context);
                    imageView.setImageResource(imageIDs[position]);
                    imageView.setLayoutParams(new Gallery.LayoutParams(100, 100));
                    imageView.setBackgroundResource(itemBackground);
                    return imageView;
                }
            }
        }

activity_main.xml:-

<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="${relativePackage}.${activityClass}"
            android:orientation="vertical" >

            <Gallery
                android:id="@+id/gallery1"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content" />

            <ImageView
                android:id="@+id/image1"
                android:layout_width="215dp"
                android:layout_height="315dp"
                android:layout_gravity="center_horizontal"
                android:background="#cfcfcf"
                android:paddingTop="5dp"
                android:paddingBottom="5dp"
                android:paddingLeft="10dp"
                android:paddingRight="10dp"
                android:src="@drawable/pic1" />

        </LinearLayout>

在 res->values->attrs.xml 添加以下行：-

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MyGallery">
    <attr name="android:galleryItemBackground" />
    </declare-styleable>  
</resources>