項(xiàng)目中使用的TabActivity已經(jīng)被Google棄用掠抬，最近嘗試著轉(zhuǎn)換 ViewPager+Fragment，解決了以下問題
ViewPager禁止滑動(dòng)
項(xiàng)目中主界面不要左右滑動(dòng)聘鳞，但是ViewPager沒有官方api來控制滑動(dòng)薄辅，需要自定義ViewPager，重寫幾個(gè)方法
/**
* 無法左右滑動(dòng)的ViewPager
*/
public class NoScrollViewPager extends ViewPager {
public NoScrollViewPager(Context context) {
super(context);
}
public NoScrollViewPager(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean onTouchEvent(MotionEvent arg0) {
return false;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent arg0) {
return false;
}
}
Fragment是否可見
項(xiàng)目中一個(gè)頁面里面有輪播圖抠璃，當(dāng)界面不可見時(shí)站楚，停止輪播，當(dāng)界面可見時(shí)搏嗡，開始輪播窿春。
注意：當(dāng)我們使用ViewPager+Fragment時(shí)，如果Fragment.onStart()被調(diào)用了采盒，只是綁定的Activity可見了旧乞，當(dāng)前Fragment不一定可見。
這里需要借助Fragment.setUserVisibleHint(boolean isVisibleToUser)這個(gè)方法磅氨。假如ViewPager中有兩個(gè)Fragment分別為A良蛮，B，做簡單測(cè)試悍赢，測(cè)試setUserVisibleHint調(diào)用時(shí)機(jī)：
ViewPager初始化
A.setUserVisibleHint(false)
B.setUserVisibleHint(false)
A.onCreate()
A.onAttach()
A.setUserVisibleHint(true)
B.onCreate()
B.onAttach()
B.onCreateView()
A.onCreateView()
切換A到B
A.setUserVisibleHint(false)
B.setUserVisibleHint(true)
綁定Activity變?yōu)椴豢梢?/h4>
未調(diào)用fragment.setUserVisibleHint
綁定Activity變?yōu)榭梢?/h4>
未調(diào)用fragment.setUserVisibleHint
總結(jié)
- onAttach()之前决瞳，ViewPager中的每個(gè)Fragment會(huì)被調(diào)用setUserVisibleHint(false)
- onCreateView()之前，如果fragment為當(dāng)前頁左权，則再次被調(diào)用setUserVisibleHint(true)
- ViewPager的fragment之間進(jìn)行切換皮胡，調(diào)用fragment.setUserVisibleHint(true or false)
- 綁定Activity前后臺(tái)切換時(shí)
不調(diào)用fragment.setUserVisibleHint
Fragment是否可見還需要結(jié)合fragment.onResume()以及fragment.onStop()進(jìn)行判斷，這兩個(gè)方法的調(diào)用跟在Activity相應(yīng)方法之后赏迟，得出代碼如下
private boolean isUiPrepared;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_index, container, false);
isUiPrepared = true;
return view;
}
@Override
public void onResume() {
super.onResume();
setUserVisibleHint(getUserVisibleHint());
}
@Override
public void onStop() {
super.onStop();
// fragment 真的不可見了
}
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isUiPrepared) {//onCreateView調(diào)用之后才執(zhí)行
if (isVisibleToUser) {
// fragment 真的可見了
} else {
// fragment 真的不可見了
}
}
}
懶加載
LazyFragment是實(shí)現(xiàn)了懶加載效果的Fragment屡贺，@CallSuper用于檢測(cè)子類是否有調(diào)用父類的方法，如果未調(diào)用锌杀，IDE會(huì)給錯(cuò)誤提示
/**
* 懶加載fragment<br>
* 作用：如果fragment不可見時(shí)甩栈，不加載數(shù)據(jù)；可見時(shí)再加載數(shù)據(jù)<br>
* 使用：<br>
* <ul>
* <li>繼承LazyFragment糕再，在{@link LazyFragment#loadData()}加載數(shù)據(jù)<br>
* <li>onCreateView中只完成ui的操作量没，不加載數(shù)據(jù)
* </ul>
*/
public abstract class LazyFragment extends Fragment {
protected Activity activity;
protected LazyFragment fragment;
private boolean isInited;
private boolean isUiPrepared;
@Override
public void onAttach(Context context) {
super.onAttach(context);
this.activity = (Activity) context;
fragment = this;
}
@CallSuper
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
isUiPrepared = true;
lazyLoad();
}
public void lazyLoad() {
if (getUserVisibleHint() && isUiPrepared && !isInited) {
// 異步初始化，在初始化后顯示正常UI
isInited = loadData();
}
}
/**
* 當(dāng)fragment可見突想，ui已經(jīng)完成殴蹄，數(shù)據(jù)還未初始化時(shí)，回調(diào)此方法<br/>
* 可以主動(dòng)調(diào)用{@link LazyFragment#setInited(boolean)}設(shè)置
* @return 是否初始化成功猾担，true成功袭灯，false失敗
*/
public abstract boolean loadData();
/**
* 是否初始化成功，true成功绑嘹，false失敗
* @param inited
*/
public void setInited(boolean inited) {
isInited = inited;
}
public boolean isInited() {
return isInited;
}
@CallSuper
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
lazyLoad();
}
}
}
