Android_fragment
目录
使用Fragment 我们可以把页面结构划分成几块,每块使用一个Fragment来管理。这样我们可以更加方便的在运行过程中动态地更新Activity中的用户界面,日后迭代更新、维护也是更加方便。 Fragment并不能单独使用,他需要嵌套在Activity 中使用,尽管他拥有自己的生命周期,但是还是会受到宿主Activity的生命周期的影响,比如Activity 被destory销毁了,他也会跟着销毁!一个Activity可以嵌套多个Fragment。
1. 基本概念
2. Fragment 生命周期
①Activity加载Fragment的时候,依次调用下面的方法: onAttach -> onCreate -> onCreateView -> onActivityCreated -> onStart ->onResume
②当我们启动一个新的页面, 此时Fragment所在的Activity不可见
,会执行 onPause
③当新页面返回后,当前Activity和Fragment又可见了
,会再次执行onStart和 onResume
⑥退出了Activity的话,那么Fragment将会被完全结束, Fragment会进入销毁状态
onPause -> onStop -> onDestoryView -> onDestory -> onDetach
3. 创建Fragment
.1. 静态加载
- 自定义Fragment 类
public class Fragmentone extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment1, container,false);
return view;
}
}
- 在需要加载Fragment Activity 对应的布局文件中添加对应的fragment的标签
<fragment
android:id="@+id/fragment1"
android:name="com.jay.example.fragmentdemo.Fragmentone" #属性是全限定类名,就是要包含Fragment的包名
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />
.2. 动态加载Fragment类
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Display dis = getWindowManager().getDefaultDisplay();
if(dis.getWidth() > dis.getHeight())
{
Fragment1 f1 = new Fragment1();
getFragmentManager().beginTransaction().replace(R.id.LinearLayout1, f1).commit();
}
else
{
Fragment2 f2 = new Fragment2();
getFragmentManager().beginTransaction().replace(R.id.LinearLayout1, f2).commit();
}
}
}
4. 数据传输
.1. activity->fragment
// 步骤1:获取FragmentManager
FragmentManager fragmentManager = getFragmentManager();
// 步骤2:获取FragmentTransaction
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
// 步骤3:创建需要添加的Fragment
final mFragment fragment = new mFragment();
// 步骤4:创建Bundle对象
// 作用:存储数据,并传递到Fragment中
Bundle bundle = new Bundle();
// 步骤5:往bundle中添加数据
bundle.putString("message", "I love Google");
// 步骤6:把数据设置到Fragment中
fragment.setArguments(bundle);
// 步骤7:动态添加fragment
// 即将创建的fragment添加到Activity布局文件中定义的占位符中(FrameLayout)
fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();
public class mFragment extends Fragment {
Button button;
TextView text;
Bundle bundle;
String message;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View contentView = inflater.inflate(R.layout.fragment, container, false);
// 设置布局文件
button = (Button) contentView.findViewById(R.id.button);
text = (TextView) contentView.findViewById(R.id.text);
// 步骤1:通过getArgments()获取从Activity传过来的全部值
bundle = this.getArguments();
// 步骤2:获取某一值
message = bundle.getString("message");
// 步骤3:设置按钮,将设置的值显示出来
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// 显示传递过来的值
text.setText(message);
}
});
return contentView;
}
}
.2. fragment->activity
- 设置回调接口
public interface ICallBack {
void get_message_from_Fragment(String string);
}
- 设置fragment类
public class mFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View contentView = inflater.inflate(R.layout.fragment, container, false);
// 设置布局文件
return contentView;
}
// 设置 接口回调 方法
public void sendMessage(ICallBack callBack){
callBack.get_message_from_Fragment("消息:我来自Fragment");
}
}
// 步骤1:获取FragmentManager
FragmentManager fragmentManager = getFragmentManager();
// 步骤2:获取FragmentTransaction
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
// 步骤3:创建需要添加的Fragment
final mFragment fragment = new mFragment();
// 步骤4:动态添加fragment
// 即将创建的fragment添加到Activity布局文件中定义的占位符中(FrameLayout)
fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// 通过接口回调将消息从fragment发送到Activity
fragment.sendMessage(new ICallBack() {
@Override
public void get_message_from_Fragment(String string) {
text.setText(string);
}
});
}
});
.3. Fragment-Activity 菜单问题
- https://blog.csdn.net/fei20121106/article/details/54580385 具体解释
- 想让
Fragment
中的onCreateOptionsMenu生效必须先调用setHasOptionsMenu
方法 - Fragment和Activity一样,可以重写onCreateOptionsMenu方法来设定自己的菜单,其实这两个地方使用onCreateOptionsMenu的目的和效果都是完全一样的
- 如果Fragment和Activity都同时
inflate
了一个menu资源文件,那么menu资源
所包含的菜单会出现两次
5. Adapter 作用
1. BaseAdapter
1. 源码
public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {
private final DataSetObservable mDataSetObservable = new DataSetObservable();
private CharSequence[] mAutofillOptions;
public boolean hasStableIds() {
return false;
}
public void registerDataSetObserver(DataSetObserver observer) {
mDataSetObservable.registerObserver(observer);
}
public void unregisterDataSetObserver(DataSetObserver observer) {
mDataSetObservable.unregisterObserver(observer);
}
/**
* Notifies the attached observers that the underlying data has been changed
* and any View reflecting the data set should refresh itself.
*/
public void notifyDataSetChanged() {
mDataSetObservable.notifyChanged();
}
/**
* Notifies the attached observers that the underlying data is no longer valid
* or available. Once invoked this adapter is no longer valid and should
* not report further data set changes.
*/
public void notifyDataSetInvalidated() {
mDataSetObservable.notifyInvalidated();
}
public boolean areAllItemsEnabled() {
return true;
}
public boolean isEnabled(int position) {
return true;
}
public View getDropDownView(int position, View convertView, ViewGroup parent) {
return getView(position, convertView, parent);
}
public int getItemViewType(int position) {
return 0;
}
public int getViewTypeCount() {
return 1;
}
public boolean isEmpty() {
return getCount() == 0;
}
@Override
public CharSequence[] getAutofillOptions() {
return mAutofillOptions;
}
/**
* Sets the value returned by {@link #getAutofillOptions()}
*/
public void setAutofillOptions(@Nullable CharSequence... options) {
mAutofillOptions = options;
}
}
public class DataSetObservable extends Observable<DataSetObserver> {
/**
* Invokes {@link DataSetObserver#onChanged} on each observer.
* Called when the contents of the data set have changed. The recipient
* will obtain the new contents the next time it queries the data set.
*/
public void notifyChanged() {
synchronized(mObservers) {
// since onChanged() is implemented by the app, it could do anything, including
// removing itself from {@link mObservers} - and that could cause problems if
// an iterator is used on the ArrayList {@link mObservers}.
// to avoid such problems, just march thru the list in the reverse order.
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onChanged();
}
}
}
/**
* Invokes {@link DataSetObserver#onInvalidated} on each observer.
* Called when the data set is no longer valid and cannot be queried again,
* such as when the data set has been closed.
*/
public void notifyInvalidated() {
synchronized (mObservers) {
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onInvalidated();
}
}
}
}
2. 数据binding
- https://www.examplecode.cn/2018/07/26/android-databinding-05-binding-objects/
- https://blog.51cto.com/u_15252276/5026746
2. adapter viewholder模式
- https://hellosure.github.io/android/2015/06/02/android-viewholder 直接使用,contentview 缓冲,viewholder优化
- https://blog.csdn.net/qq_26222859/article/details/46827511 关于viewholder 解释
public class ViewHolder {
// I added a generic return type to reduce the casting noise in client code
@SuppressWarnings("unchecked")
public static <T extends View> T get(View view, int id) {
SparseArray<View> viewHolder = (SparseArray<View>) view.getTag();
if (viewHolder == null) {
viewHolder = new SparseArray<View>();
view.setTag(viewHolder);
}
View childView = viewHolder.get(id);
if (childView == null) {
childView = view.findViewById(id);
viewHolder.put(id, childView);
}
return (T) childView;
}
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fr_image_list, container, false);
listView = (ListView) rootView.findViewById(android.R.id.list); //通过id找到对应的fragment view
((ListView) listView).setAdapter(new ImageAdapter(getActivity()));
listView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
startImagePagerActivity(position);
}
});
return rootView;
}
private static class ImageAdapter extends BaseAdapter {
private static final String[] IMAGE_URLS = Constants.IMAGES;
private LayoutInflater inflater;
private ImageLoadingListener animateFirstListener = new AnimateFirstDisplayListener();
private DisplayImageOptions options;
ImageAdapter(Context context) {
inflater = LayoutInflater.from(context);
options = new DisplayImageOptions.Builder()
.showImageOnLoading(R.drawable.ic_stub)
.showImageForEmptyUri(R.drawable.ic_empty)
.showImageOnFail(R.drawable.ic_error)
.cacheInMemory(true)
.cacheOnDisk(true)
.considerExifParams(true)
.displayer(new CircleBitmapDisplayer(Color.WHITE, 5))
.build();
}
@Override
public int getCount() {
return IMAGE_URLS.length;
} // 类似DataLoader 函数
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
/*当第一个view滑出屏幕时,这个view就会落到recycler中,这时convertview就不再等于null了,而是这个view了,只可惜,
每一个落到recycler中的view都会剥离掉它的值,只剩下它的型。
也就是说落到recycler中的view仍然绑定了ViewHolder对象,但是convertview里的组件的内容已经不复存在了,
需要重新设置。*/
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
View view = convertView;
final ViewHolder holder;
if (convertView == null) {
view = inflater.inflate(R.layout.item_list_image, parent, false);
holder = new ViewHolder();
holder.text = (TextView) view.findViewById(R.id.text);
holder.image = (ImageView) view.findViewById(R.id.image);
view.setTag(holder); //setTag才是将这些缓存起来供下次调用
} else {
holder = (ViewHolder) view.getTag();
}
holder.text.setText("Item " + (position + 1));
ImageLoader.getInstance().displayImage(IMAGE_URLS[position], holder.image, options, animateFirstListener);
return view;
}
}
//ViewHolder只是将需要缓存的那些view封装好
static class ViewHolder {
TextView text;
ImageView image;
}
2. PagerAdapter
- PagerAdapter主要是viewpager的适配器,而viewPager则也是在android.support.v4扩展包中新添加的一个强大的控件,可以实现控件的滑动效果,比如咱们在软件中常见的广告栏的滑动效果,用viewPager就可以实现。
private static class ImageAdapter extends PagerAdapter {
private static final String[] IMAGE_URLS = Constants.IMAGES;
private LayoutInflater inflater;
private DisplayImageOptions options;
ImageAdapter(Context context) {
inflater = LayoutInflater.from(context);
options = new DisplayImageOptions.Builder()
.showImageForEmptyUri(R.drawable.ic_empty)
.showImageOnFail(R.drawable.ic_error)
.resetViewBeforeLoading(true)
.cacheOnDisk(true)
.imageScaleType(ImageScaleType.EXACTLY)
.bitmapConfig(Bitmap.Config.RGB_565)
.considerExifParams(true)
.displayer(new FadeInBitmapDisplayer(300))
.build();
}
// PagerAdapter只缓存三张要显示的图片,如果滑动的图片超出了缓存的范围,就会调用这个方法,将图片销毁
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
@Override
public int getCount() {
return IMAGE_URLS.length;
}
// 当要显示的图片可以进行缓存的时候,会调用这个方法进行显示图片的初始化,我们将要显示的ImageView加入到ViewGroup中,然后作为返回值返回即可
@Override
public Object instantiateItem(ViewGroup view, int position) {
View imageLayout = inflater.inflate(R.layout.item_pager_image, view, false);
assert imageLayout != null;
ImageView imageView = (ImageView) imageLayout.findViewById(R.id.image);
final ProgressBar spinner = (ProgressBar) imageLayout.findViewById(R.id.loading);
ImageLoader.getInstance().displayImage(IMAGE_URLS[position], imageView, options, new SimpleImageLoadingListener() {
@Override
public void onLoadingStarted(String imageUri, View view) {
spinner.setVisibility(View.VISIBLE);
}
@Override
public void onLoadingFailed(String imageUri, View view, FailReason failReason) {
String message = null;
switch (failReason.getType()) {
case IO_ERROR:
message = "Input/Output error";
break;
case DECODING_ERROR:
message = "Image can't be decoded";
break;
case NETWORK_DENIED:
message = "Downloads are denied";
break;
case OUT_OF_MEMORY:
message = "Out Of Memory error";
break;
case UNKNOWN:
message = "Unknown error";
break;
}
Toast.makeText(view.getContext(), message, Toast.LENGTH_SHORT).show();
spinner.setVisibility(View.GONE);
}
@Override
public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
spinner.setVisibility(View.GONE);
}
});
view.addView(imageLayout, 0);
return imageLayout;
}
// 来判断显示的是否是同一张图片,这里我们将两个参数相比较返回即可
@Override
public boolean isViewFromObject(View view, Object object) {
return view.equals(object);
}
@Override
public void restoreState(Parcelable state, ClassLoader loader) {
}
@Override
public Parcelable saveState() {
return null;
}
}