輪播圖是 Android 常用功能之一，效果大概是這樣的：

之前我封裝寫了一個，基本達到了要求，是繼承了 Fragment（當時腦袋肯定鏽掉了），裡面 Viewpager add Fragment，這次專案多處有輪播圖，發現之前封裝的不夠用，簡直漏洞百出：1、比如底部 point 的位置，之前固定在中間，現在可能要放在右下角，point 最好也能動態改圖片；2、現在專案跟微信一樣，底部 tab 切換，中間是 Fragment 替換，發現輪播圖有問題，Fragment A 迴圈的 point 的 positoin 居然影響到了 Fragment B，照理，這是兩個 BannerFragment，不會影響的啊，報以下錯誤：

java.lang.IllegalStateException: The application`s PagerAdapter changed the adapter`s 
contents without calling PagerAdapter#notifyDataSetChanged!

經過排查，找到了原因，因為 Viewpager add Fragment 我全部放在一個類，因此：

public static List<Object> bannerList = new ArrayList<>();

這裡 static 壞事了，之前一個 banner 沒有暴露出來。3、繼承了 Fragment，引用比較麻煩，Fragment 有兩者引用方法，xml 和程式碼，兩者方式 addData 卻報錯；4、banner 沒有寫點選回撥。

再次封裝

綜合以上問題，我進行了優化，繼承 LinearLayout，當一個控制元件來引用，省去不必要的麻煩，底部 point 的位置可以設定：

pointLayout.setGravity(bannerPointGravity);

另外自定義了屬性，動態設定 point 大小和圖片，輪播圖迴圈時間，也能程式碼設定，完整程式碼示例：

 * Created by WuXiaolong on 2017/8/24.
 * 個人部落格：http：//wuxiaolong.me
 */

public class BannerLayout extends LinearLayout {

    private ViewPager viewPager;
    private LinearLayout pointLayout;
    private ScheduledExecutorService scheduler;
    private int mPosition = 0;
    private int mBannerCount = 1;
    private Context context;
    private Activity activity;
    private int bannerPointSize;
    private int bannerPointGravity;
    private int bannerPointDrawableSelected, bannerPointDrawableUnselected;
    private int bannerDelaySecond;

    public BannerLayout(Context context) {
        this(context, null);

    }

    public BannerLayout(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public BannerLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView(context, attrs);
    }

    private void initView(Context context, AttributeSet attrs) {
        this.context = context;
        activity = (Activity) context;
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.BannerLayout);
        bannerPointSize = typedArray.getDimensionPixelSize(R.styleable.BannerLayout_bannerPointSize, 10);
        bannerPointGravity = typedArray.getInt(R.styleable.BannerLayout_bannerPointGravity, Gravity.CENTER);
        bannerDelaySecond = typedArray.getInt(R.styleable.BannerLayout_bannerDelaySecond, 5);
        bannerPointDrawableSelected = typedArray.getResourceId(R.styleable.BannerLayout_bannerPointDrawableSelected, R.mipmap.point01);
        bannerPointDrawableUnselected = typedArray.getResourceId(R.styleable.BannerLayout_bannerPointDrawableUnselected, R.mipmap.point02);
        typedArray.recycle();
        View view = View.inflate(context, R.layout.banner_view_pager, null);
        addView(view);
        viewPager = (ViewPager) view.findViewById(R.id.viewPager);
        pointLayout = (LinearLayout) view.findViewById(R.id.pointLayout);
        pointLayout.setGravity(bannerPointGravity);
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            }

            @Override
            public void onPageSelected(int position) {
                addPointLayout(position);
            }

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

    public void start(List<Object> bannerList) {
        bannerShutdown();
        mBannerCount = bannerList.size();
        BannerPagerAdapter bannerPagerAdapter = new BannerPagerAdapter(context, bannerList);
        viewPager.setAdapter(bannerPagerAdapter);

        addPointLayout(0);
        startScheduler();
    }

    private void addPointLayout(int position) {

        pointLayout.removeAllViews();
        for (int i = 0; i < mBannerCount; i++) {
            ImageView imageView = new ImageView(context);
            LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(bannerPointSize, bannerPointSize);
            layoutParams.setMargins(10, 0, 0, 0);
            imageView.setLayoutParams(layoutParams);

            if (position == i) {
                imageView.setImageResource(bannerPointDrawableSelected);
            } else {
                imageView.setImageResource(bannerPointDrawableUnselected);
            }
            pointLayout.addView(imageView);
        }

    }

    private void startScheduler() {
        scheduler = Executors.newSingleThreadScheduledExecutor();
        scheduler.scheduleAtFixedRate(new Runnable() {

            @Override
            public void run() {
                mPosition = viewPager.getCurrentItem();
                if (mPosition < mBannerCount - 1) {
                    mPosition++;
                } else {
                    mPosition = 0;
                }

                activity.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        viewPager.setCurrentItem(mPosition);
                    }
                });
            }
        }, 1, bannerDelaySecond, TimeUnit.SECONDS);
    }

    public void bannerShutdown() {
        if (scheduler != null)
            scheduler.shutdown();
    }

    private class BannerPagerAdapter extends PagerAdapter {
        private List<Object> bannerList = new ArrayList<>();
        private Context context;

        BannerPagerAdapter(Context context, List<Object> bannerList) {
            this.context = context;
            this.bannerList.clear();
            this.bannerList.addAll(bannerList);
        }

        @Override
        public int getCount() {
            return bannerList.size();
        }

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

        @Override
        public Object instantiateItem(ViewGroup container, final int position) {
            ImageView imageView = new ImageView(context);
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            Object object = bannerList.get(position);
            //這裡我封裝了 Glide 4.0 的工具類，用於顯示圖片
            ImageLoaderUtil.load(context, object, imageView);
            container.addView(imageView);

            return imageView;
        }

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

    public int dp2px(float var0) {
        float var1 = context.getResources().getDisplayMetrics().density;
        return (int) (var0 * var1 + 0.5F);
    }

    public void setBannerPointSize(int bannerPointSize) {
        this.bannerPointSize = dp2px(bannerPointSize);
    }

    public void setBannerPointGravity(int bannerPointGravity) {
        this.bannerPointGravity = bannerPointGravity;
        pointLayout.setGravity(bannerPointGravity);
    }

    public void setBannerPointDrawableSelected(int bannerPointDrawableSelected) {
        this.bannerPointDrawableSelected = bannerPointDrawableSelected;
    }

    public void setBannerPointDrawableUnselected(int bannerPointDrawableUnselected) {
        this.bannerPointDrawableUnselected = bannerPointDrawableUnselected;
    }

    public void setBannerDelaySecond(int bannerDelaySecond) {
        this.bannerDelaySecond = bannerDelaySecond;
    }

}

其中自定義屬性的attrs.xml：

<resources>

    <declare-styleable name="BannerLayout">
        <!--輪播圖點的大小-->
        <attr name="bannerPointSize" format="dimension" />
        <!--輪播圖點的位置，分別有左中右-->
        <attr name="bannerPointGravity" format="enum">
            <enum name="left" value="3" />
            <enum name="center" value="17" />
            <enum name="right" value="5" />
        </attr>
        <!--輪播圖點選中的圖片-->
        <attr name="bannerPointDrawableSelected" format="reference" />
        <!--輪播圖點未選中的圖片-->
        <attr name="bannerPointDrawableUnselected" format="reference" />
        <!--輪播圖迴圈時間，單位秒-->
        <attr name="bannerDelaySecond" format="integer" />
    </declare-styleable>
</resources>

使用說明

xml

<com.wuxiaolong.bannersample.BannerLayout
    android:id="@+id/bannerView"
    android:layout_width="match_parent"
    android:layout_height="198dp"
    app:bannerDelaySecond="3"
    app:bannerPointDrawableSelected="@drawable/gray_radius"
    app:bannerPointDrawableUnselected="@drawable/white_radius"
    app:bannerPointGravity="right"
    app:bannerPointSize="10dp" />

呼叫：

public class MainActivity extends AppCompatActivity {
    private BannerLayout bannerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bannerView = (BannerLayout) findViewById(R.id.bannerView);
        List<Object> bannerList = new ArrayList<>();
        bannerList.add(R.mipmap.horizontal_default);
        bannerList.add("http://pic1.win4000.com/wallpaper/5/598161750eddb.jpg");
        bannerList.add("http://pic1.win4000.com/wallpaper/4/597efb5b6aae8.jpg");
        bannerView.setBannerPointSize(10);
        bannerView.setBannerPointGravity(Gravity.CENTER);
        bannerView.setBannerPointDrawableSelected(R.drawable.gray_radius);
        bannerView.setBannerPointDrawableUnselected(R.mipmap.point01);
        bannerView.setBannerDelaySecond(5);
        //banner 設定方法完畢時最後呼叫 start 方法
        bannerView.start(bannerList);
    }

    @Override
    protected void onStop() {
        super.onStop();
        bannerView.bannerShutdown();
    }
}

最後

歡迎加入Android進階交流群；701740775。進群可免費領取一份最新技術大綱和Android進階資料。請備註csdn