效果圖

圖片展示形式

1、當只有1張圖時，可以自己定製圖片寬高，也可以使用預設九宮格的寬高；
2、當只有4張圖時，以2*2的方式顯示；
3、除以上兩種情況下，都是按照3列方式顯示，但這時有一些細節：
    a、如果只有9張圖，當然是以3*3的方式顯示；
    b、如果超過9張圖，可以設定是否全部顯示。
        如果設定不完全顯示，則按照3*3的方式顯示，但是在第9張圖上會有一個帶“+”號的數字，
        代表還有幾張沒有顯示，這裡是模仿了QQ空間圖片超出9張的顯示方式；
        如果設定全部顯示，理所當然的將所有圖片都顯示出來。
4、圖片被按下時，會有一個變暗的效果，這也是模仿微信朋友圈的效果。
 

專案中使用

111111，自定義控制元件NineGridLayout的建立

該控制元件為自定義控制元件，因此不需要新增什麼依賴或者作為Library引入，只需要按照如下方式定義一個NineGridLayout的抽象類，然後按照專案需求建立該抽象類的子類即可。
1，建立抽象類NineGridLayout，繼承自ViewGroup，程式碼如下：

public abstract class NineGridLayout extends ViewGroup {

    // 預設圖片之間的間隙為3f
    private static final float DEFUALT_SPACING = 3f
 
;
    private static final int MAX_COUNT = 9;

    protected Context mContext;
    private float mSpacing = DEFUALT_SPACING;
    private int mColumns;
    private int mRows;
    private int mTotalWidth;
    private int mSingleWidth;

    private boolean mIsShowAll = false;
    private boolean mIsFirst =
 
 true;
    private List<String> mUrlList = new ArrayList<>();

    public NineGridLayout(Context context) {
        super(context);
        init(context);
    }

    public NineGridLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.NineGridLayout);

        mSpacing = typedArray.getDimension(R.styleable.NineGridLayout_spacing, DEFUALT_SPACING);
        typedArray.recycle();
        init(context);
    }

    private void init(Context context) {
        mContext = context;
        if (getListSize(mUrlList) == 0) {
            setVisibility(GONE);
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        mTotalWidth = right - left;
        mSingleWidth = (int) ((mTotalWidth - mSpacing * (3 - 1)) / 3);
        if (mIsFirst) {
            notifyDataSetChanged();
            mIsFirst = false;
        }
    }

    /**
     * 設定間隔
     *
     * @param spacing
     */
    public void setSpacing(float spacing) {
        mSpacing = spacing;
    }

    /**
     * 設定是否顯示所有圖片（超過最大數時）
     *
     * @param isShowAll
     */
    public void setIsShowAll(boolean isShowAll) {
        mIsShowAll = isShowAll;
    }

    public void setUrlList(List<String> urlList) {
        if (getListSize(urlList) == 0) {
            setVisibility(GONE);
            return;
        }
        setVisibility(VISIBLE);

        mUrlList.clear();
        mUrlList.addAll(urlList);

        if (!mIsFirst) {
            notifyDataSetChanged();
        }
    }

    public void notifyDataSetChanged() {
        post(new TimerTask() {
            @Override
            public void run() {
                refresh();
            }
        });
    }

    private void refresh() {
        removeAllViews();
        int size = getListSize(mUrlList);
        if (size > 0) {
            setVisibility(VISIBLE);
        } else {
            setVisibility(GONE);
        }

        if (size == 1) {
            String url = mUrlList.get(0);
            RatioImageView imageView = createImageView(0, url);

            //避免在ListView中一張圖未載入成功時，佈局高度受其他item影響
            LayoutParams params = getLayoutParams();
            params.height = mSingleWidth;
            setLayoutParams(params);
            imageView.layout(0, 0, mSingleWidth, mSingleWidth);

            boolean isShowDefualt = displayOneImage(imageView, url, mTotalWidth);
            if (isShowDefualt) {
                layoutImageView(imageView, 0, url, false);
            } else {
                addView(imageView);
            }
            return;
        }

        generateChildrenLayout(size);
        layoutParams();

        for (int i = 0; i < size; i++) {
            String url = mUrlList.get(i);
            RatioImageView imageView;
            if (!mIsShowAll) {
                if (i < MAX_COUNT - 1) {
                    imageView = createImageView(i, url);
                    layoutImageView(imageView, i, url, false);
                } else { //第9張時
                    if (size <= MAX_COUNT) {//剛好第9張
                        imageView = createImageView(i, url);
                        layoutImageView(imageView, i, url, false);
                    } else {//超過9張
                        imageView = createImageView(i, url);
                        layoutImageView(imageView, i, url, true);
                        break;
                    }
                }
            } else {
                imageView = createImageView(i, url);
                layoutImageView(imageView, i, url, false);
            }
        }
    }

    private void layoutParams() {
        int singleHeight = mSingleWidth;

        //根據子view數量確定高度
        LayoutParams params = getLayoutParams();
        params.height = (int) (singleHeight * mRows + mSpacing * (mRows - 1));
        setLayoutParams(params);
    }

    private RatioImageView createImageView(final int i, final String url) {
        RatioImageView imageView = new RatioImageView(mContext);
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        imageView.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                onClickImage(i, url, mUrlList);
            }
        });
        return imageView;
    }

    /**
     * @param imageView
     * @param url
     * @param showNumFlag 是否在最大值的圖片上顯示還有未顯示的圖片張數
     */
    private void layoutImageView(RatioImageView imageView, int i, String url, boolean showNumFlag) {
        final int singleWidth = (int) ((mTotalWidth - mSpacing * (3 - 1)) / 3);
        int singleHeight = singleWidth;

        int[] position = findPosition(i);
        int left = (int) ((singleWidth + mSpacing) * position[1]);
        int top = (int) ((singleHeight + mSpacing) * position[0]);
        int right = left + singleWidth;
        int bottom = top + singleHeight;

        imageView.layout(left, top, right, bottom);

        addView(imageView);
        if (showNumFlag) {//新增超過最大顯示數量的文字
            int overCount = getListSize(mUrlList) - MAX_COUNT;
            if (overCount > 0) {
                float textSize = 30;
                final TextView textView = new TextView(mContext);
                textView.setText("+" + String.valueOf(overCount));
                textView.setTextColor(Color.WHITE);
                textView.setPadding(0, singleHeight / 2 - getFontHeight(textSize), 0, 0);
                textView.setTextSize(textSize);
                textView.setGravity(Gravity.CENTER);
                textView.setBackgroundColor(Color.BLACK);
                textView.getBackground().setAlpha(120);

                textView.layout(left, top, right, bottom);
                addView(textView);
            }
        }
        displayImage(imageView, url);
    }

    private int[] findPosition(int childNum) {
        int[] position = new int[2];
        for (int i = 0; i < mRows; i++) {
            for (int j = 0; j < mColumns; j++) {
                if ((i * mColumns + j) == childNum) {
                    position[0] = i;//行
                    position[1] = j;//列
                    break;
                }
            }
        }
        return position;
    }

    /**
     * 根據圖片個數確定行列數量
     *
     * @param length
     */
    private void generateChildrenLayout(int length) {
        if (length <= 3) {
            mRows = 1;
            mColumns = length;
        } else if (length <= 6) {
            mRows = 2;
            mColumns = 3;
            if (length == 4) {
                mColumns = 2;
            }
        } else {
            mColumns = 3;
            if (mIsShowAll) {
                mRows = length / 3;
                int b = length % 3;
                if (b > 0) {
                    mRows++;
                }
            } else {
                mRows = 3;
            }
        }

    }

    protected void setOneImageLayoutParams(RatioImageView imageView, int width, int height) {
        imageView.setLayoutParams(new LayoutParams(width, height));
        imageView.layout(0, 0, width, height);

        LayoutParams params = getLayoutParams();
//        params.width = width;
        params.height = height;
        setLayoutParams(params);
    }

    private int getListSize(List<String> list) {
        if (list == null || list.size() == 0) {
            return 0;
        }
        return list.size();
    }

    private int getFontHeight(float fontSize) {
        Paint paint = new Paint();
        paint.setTextSize(fontSize);
        Paint.FontMetrics fm = paint.getFontMetrics();
        return (int) Math.ceil(fm.descent - fm.ascent);
    }

    /**
     * @param imageView
     * @param url
     * @param parentWidth 父控制元件寬度
     * @return true 代表按照九宮格預設大小顯示，false 代表按照自定義寬高顯示
     */
    protected abstract boolean displayOneImage(RatioImageView imageView, String url, int parentWidth);

    protected abstract void displayImage(RatioImageView imageView, String url);

    protected abstract void onClickImage(int position, String url, List<String> urlList);
}

2，根據寬高自動計算比例的ImageView：

public class RatioImageView extends ImageView {

    /**
     * 寬高比例
     */
    private float mRatio = 0f;

    public RatioImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public RatioImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.RatioImageView);

        mRatio = typedArray.getFloat(R.styleable.RatioImageView_ratio, 0f);
        typedArray.recycle();
    }

    public RatioImageView(Context context) {
        super(context);
    }

    /**
     * 設定ImageView的寬高比
     *
     * @param ratio
     */
    public void setRatio(float ratio) {
        mRatio = ratio;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int width = MeasureSpec.getSize(widthMeasureSpec);
        if (mRatio != 0) {
            float height = width / mRatio;
            heightMeasureSpec = MeasureSpec.makeMeasureSpec((int) height, MeasureSpec.EXACTLY);
        }
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Drawable drawable = getDrawable();
                if (drawable != null) {
                    drawable.mutate().setColorFilter(Color.GRAY,
                            PorterDuff.Mode.MULTIPLY);
                }
                break;
            case MotionEvent.ACTION_MOVE:
                break;
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                Drawable drawableUp = getDrawable();
                if (drawableUp != null) {
                    drawableUp.mutate().clearColorFilter();
                }
                break;
        }

        return super.onTouchEvent(event);
    }
}

3，新增該自定義控制元件用到的兩個自定義屬性，在res/values/attrs.xml中新增如下程式碼：

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <declare-styleable name="RatioImageView">
        <attr name="ratio" format="float"/>
    </declare-styleable>

    <declare-styleable name="NineGridLayout">
        <attr name="spacing" format="dimension"/>
    </declare-styleable>
</resources>

222222，開始使用上面的自定義九宮格控制元件NineGridLayout

1，繼承我們的自定義控制元件抽象類定義對應的子類，實現裡面的三個方法，程式碼如下所示，GitHub官網上給出的例子使用的圖片載入框架是ImageLoader，這裡我採用使用Glide的方式，關於Glide框架監聽在實際專案中的使用，不理解的同