Android ViewGroup删除子视图时应该谨慎的一个问题
发布时间:2021-11-25 20:06:59 所属栏目:教程 来源:互联网
导读: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
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); (编辑:济南站长网) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |