类似微信朋友圈，点击+号图片，可以加图片

xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="40dp"
android:orientation="vertical" >

<com.sw.demo.widget.NinePhotoView
    android:id="@+id/photoview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:ninephoto_hspace="10dp"
    app:ninephoto_vspace="10dp"
    app:rainbowbar_color="@android:color/holo_blue_bright" >

</com.sw.demo.widget.NinePhotoView>

NinePhotoView.java

public class NinePhotoView extends ViewGroup {

public static final int MAX_PHOTO_NUMBER = 9;

private int[] constImageIds = { R.drawable.girl_0, R.drawable.girl_1,
      R.drawable.girl_2, R.drawable.girl_3, R.drawable.girl_4,
      R.drawable.girl_5, R.drawable.girl_6, R.drawable.girl_7,
      R.drawable.girl_8 };

// horizontal space among children views
int hSpace = Utils.dpToPx(10, getResources());
// vertical space among children views
int vSpace = Utils.dpToPx(10, getResources());

// every child view width and height.
int childWidth = 0;
int childHeight = 0;

// store images res id
ArrayList<integer> mImageResArrayList = new ArrayList<integer>(9);
private View addPhotoView;

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

public NinePhotoView(Context context, AttributeSet attrs) {
  this(context, attrs, 0);
}

public NinePhotoView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);

  TypedArray t = context.obtainStyledAttributes(attrs,
          R.styleable.NinePhotoView, 0, 0);
  hSpace = t.getDimensionPixelSize(
          R.styleable.NinePhotoView_ninephoto_hspace, hSpace);
  vSpace = t.getDimensionPixelSize(
          R.styleable.NinePhotoView_ninephoto_vspace, vSpace);
  t.recycle();

  addPhotoView = new View(context);
  addView(addPhotoView);
  mImageResArrayList.add(new integer());
}

Measure

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  int rw = MeasureSpec.getSize(widthMeasureSpec);
  int rh = MeasureSpec.getSize(heightMeasureSpec);

  childWidth = (rw - 2 * hSpace) / 3;
  childHeight = childWidth;

  int childCount = this.getChildCount();
  for (int i = 0; i < childCount; i++) {
      View child = this.getChildAt(i);
      //this.measureChild(child, widthMeasureSpec, heightMeasureSpec);

      LayoutParams lParams = (LayoutParams) child.getLayoutParams();
      lParams.left = (i % 3) * (childWidth + hSpace);
      lParams.top = (i / 3) * (childWidth + vSpace);
  }

  int vw = rw;
  int vh = rh;
  if (childCount < 3) {
      vw = childCount * (childWidth + hSpace);
  }
  vh = ((childCount + 3) / 3) * (childWidth + vSpace);
  setMeasuredDimension(vw, vh);
}

　　我们的子View三个一排，而且都是正方形，所以我们上面通过循环很好去得到所有子View的位置，注意我们上面把子View的左上角坐标存储到我们自定义的LayoutParams 的left和top二个字段中，Layout阶段会使用，最后我们算得整个ViewGroup的宽高，调用setMeasuredDimension设置。　　

　

Layout

@Override
protected void onLayout(boolean arg0, int arg1, int arg2, int arg3, int arg4) {
  int childCount = this.getChildCount();
  for (int i = 0; i < childCount; i++) {
      View child = this.getChildAt(i);
      LayoutParams lParams = (LayoutParams) child.getLayoutParams();
      child.layout(lParams.left, lParams.top, lParams.left + childWidth,
              lParams.top + childHeight);

      if (i == mImageResArrayList.size() - 1 && mImageResArrayList.size() != MAX_PHOTO_NUMBER) {
          child.setBackgroundResource(R.drawable.add_photo);
          child.setOnClickListener(new View.OnClickListener() {

              @Override
              public void onClick(View arg0) {
                  addPhotoBtnClick();
              }
          });
      }else {
          child.setBackgroundResource(constImageIds[i]);
          child.setOnClickListener(null);
      }
  }
}

public void addPhoto() {
  if (mImageResArrayList.size() < MAX_PHOTO_NUMBER) {
      View newChild = new View(getContext());
      addView(newChild);
      mImageResArrayList.add(new integer());
      requestLayout();
      invalidate();
  }
}

public void addPhotoBtnClick() {
  final CharSequence[] items = { "Take Photo", "Photo from gallery" };

  AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
  builder.setItems(items, new DialogInterface.OnClickListener() {

      @Override
      public void onClick(DialogInterface arg0, int arg1) {
          addPhoto();
      }

  });
  builder.show();
}

　　最核心的就是调用layout方法，根据我们measure阶段获得的LayoutParams中的left和top字段，也很好对每个子View进行位置排列。然后判断在图片未达到最大值9张时，默认最后一张是+号图片，然后设置点击事件，弹出对话框供用户选择操作。

Draw
不需要重写，使用ViewGroup默认实现即可。