重新设计应用程序后,我们在创建新 View 时的加载时间更长(旧版本几乎没有图像,而且速度更快)。我们使用 ViewFlipper 来浏览 View 。创建的前两个 View 是两个带有 ListView 的布局,其元素具有背景图像和其他图形。巧合的是,我们发现每次创建新 View 并将其放入 View 堆栈时,应用程序都会计算每个现有 View 的尺寸(其中多次调用 ListView 适配器的 getView() 方法)。每次调用的跟踪日志如下所示:
LinearLayout.measureChildBeforeLayout(View, int, int, int, int, int) line: 1369 LinearLayout.measureVertical(int, int) line: 660 LinearLayout.onMeasure(int, int) line: 553 LinearLayout(View).measure(int, int) line: 12937 TabHost(ViewGroup).measureChildWithMargins(View, int, int, int, int) line: 5045 TabHost(FrameLayout).onMeasure(int, int) line: 293 TabHost(View).measure(int, int) line: 12937 RelativeLayout.measureChildHorizontal(View, RelativeLayout$LayoutParams, int, int) line: 594 RelativeLayout.onMeasure(int, int) line: 376 RelativeLayout(View).measure(int, int) line: 12937 FrameLayout(ViewGroup).measureChildWithMargins(View, int, int, int, int) line: 5045 FrameLayout.onMeasure(int, int) line: 293 FrameLayout(View).measure(int, int) line: 12937 LinearLayout(ViewGroup).measureChildWithMargins(View, int, int, int, int) line: 5045 LinearLayout.measureChildBeforeLayout(View, int, int, int, int, int) line: 1369 LinearLayout.measureVertical(int, int) line: 660 LinearLayout.onMeasure(int, int) line: 553 LinearLayout(View).measure(int, int) line: 12937 PhoneWindow$DecorView(ViewGroup).measureChildWithMargins(View, int, int, int, int) line: 5045 PhoneWindow$DecorView(FrameLayout).onMeasure(int, int) line: 293 PhoneWindow$DecorView.onMeasure(int, int) line: 2180 PhoneWindow$DecorView(View).measure(int, int) line: 12937
等等... 我认为这就是应用程序变得如此缓慢的原因。 我可以做些什么来阻止应用执行这些措施或使应用更快?
ListAdapter getView():
public View getView(int pos, View convertView, ViewGroup parent) {
View row;
Entry entry = null;
if (objects.get(pos) instanceof Entry) {
entry = (Entry) objects.get(pos) ;
Boolean isGroupedEntry;
if (entry.getGroup() != null && entry.isGroupedEntry()) {
isGroupedEntry = true;
} else {
isGroupedEntry = false;
}
if (convertView != null) {
row = convertView;
} else {
row = new EntryBoxFrameLayout(getContext());
}
((EntryBoxFrameLayout) row).configureFor(entry);
} else {
row = new View(ContentManager.getInstance().getContext());
}
row.setSelected(false);
row.setTag(pos);
return row;
}
在 configureFor() 中我设置了一些文本然后:
if (entry.getUserIsSignedUp() > 0) {
this.setBackgroundColor("4A4A4A");
this.findViewById(R.id.star).setVisibility(View.VISIBLE);
this.findViewById(R.id.entry_face).setBackgroundResource(R.drawable.entry_face_loggedin);
fulldate.setTextColor(Color.BLACK);
} else {
this.setBackgroundColor(entry.getColorHex());
this.findViewById(R.id.star).setVisibility(View.INVISIBLE);
this.findViewById(R.id.entry_face).setBackgroundResource(R.drawable.entry_face);
fulldate.setTextColor(Color.WHITE);
}
if (entry.getGroup() != null) {
this.findViewById(R.id.imgGroupArrow).setVisibility(View.VISIBLE);
if (entry.isGroupExpanded()) {
((ImageView)this.findViewById(R.id.imgGroupArrow)).setImageResource(R.drawable.entry_up_arrow);
} else {
((ImageView)this.findViewById(R.id.imgGroupArrow)).setImageResource(R.drawable.entry_down_arrow);
}
this.setGroupContainer(true);
} else {
this.findViewById(R.id.imgGroupArrow).setVisibility(View.INVISIBLE);
this.setGroupContainer(false);
}
String filename = entry.getCacheFilename();
Drawable entryimage = null;
if (filename != null) {
try {
FileInputStream input = ContentManager.getInstance().getContext().openFileInput(filename);
entryimage = new BitmapDrawable(ContentManager.getInstance().getContext().getResources(), input);
input.close();
} catch (Exception e) {
Log.e(e.getLocalizedMessage());
}
}
if (entryimage != null) {
this.getImageView().setImageDrawable(entryimage);
} else {
this.getImageView().setImageResource(R.drawable.entry_placeholder);
}
最佳答案
getView() 方法正在减慢您的应用程序。 listView 回收 View 对象以提高性能。
有许多学习资源涵盖了这一点。
来自 google I/O 大会和 listView 的创建者:Romain Guy
图片优化
- 从网上下载:LazyLoading
- 来自您的资源:displaying bitmaps
更多代码示例:
- Google 优化 ListView
- 用于延迟加载 ListView 的 Google
- Google for convertview, viewholder listview
关于android - 在 Android 上创建的 View 的度量,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14340225/