android ViewGroup删除子视图时应该注意的一个问题

在Activity中创建一个LinearLayout，创建一个scrollHorizon对象（scrollHorizon继承自ViewGroup），在scrollHorizon中调用createLayout函数来加载myView（继承自View）对象，然后调用deleteAllView函数来删除所有的视图。

scrollHorizon代码：

public class scrollHorizon extends ViewGroup {

private Context context;

public scrollHorizon(Context context) {
super(context);

this.context = context;

createLayout();

deleteAllView();
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {

int childCount = this.getChildCount();
int childLeft = 0;
int childTop = 0;
for(int i = 0; i < childCount; i++){
View child = getChildAt(i);
child.setVisibility(View.VISIBLE);
child.measure(r - l, b - t);
child.layout(childLeft, childTop, childLeft + child.getMeasuredWidth(),childTop + child.getMeasuredHeight());
if(childLeft <= 320){
childLeft = childLeft + child.getMeasuredWidth();
}
else{
childLeft = 0;
childTop = childTop + child.getMeasuredHeight();
}
}
}

public void createLayout(){

Resources resource = this.getResources();

PackageManager pmanager = context.getPackageManager();

final Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);

List<ResolveInfo> list = pmanager.queryIntentActivities(mainIntent, 0);

for( int i = 0; i < list.size(); i++){
int icon = R.drawable.contacts_button_normal;
LinearLayout linear = new LinearLayout(context);
linear.setLayoutParams(new LayoutParams(45, 45));
linear.setBackgroundDrawable(this.getResources().getDrawable(R.drawable.icon));

ImageView image2 = new ImageView(context);
image2.setBackgroundDrawable(this.getResources().getDrawable(R.drawable.icon));
Drawable drawable = resource.getDrawable(icon);

ImageView image = new ImageView(context);

image.setBackgroundDrawable(drawable);
linear.addView(image2);
linear.addView(image);
this.addView(linear);
}
}

public void deleteAllView(){
int size = this.getChildCount();
for( int i = 0; i < size; i++){
this.removeViewAt(i);
}
}
}

myView代码：
public class myView extends View {

public myView(Context context) {
super(context);

setLayoutParams(new LayoutParams(40,40));
}

}

主Activity代码：

public class scrollHorizonTest extends Activity {

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

LinearLayout linear = new LinearLayout(this);

scrollHorizon horizon = new scrollHorizon(this);

linear.addView(horizon);

this.setContentView(linear);
}
}

显示结果：



如果不调用deleteAllView函数，那程序没有问题，可以正常的进行显示，但调用deleteAllView函数存在空指针异常。
原因为：当你删除掉第一个View后（假设总共有两个View），当前ViewGroup的子视图只有一个，而这个子视图的位置变为0，所以当你调用removeViewAt(1)时会出现空指针异常，正确的删除方法应该是将deleteAllView函数中的removeViewAt(i)修改为removeViewAt(0);