Fragment懒加载

用于viewpager+fragment布局

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.widget.FrameLayout;

/**
 * <h1>懒加载Fragment</h1> 只有创建并显示的时候才会调用onCreateViewLazy方法<br>
 * <br>
 * <p>
 * 懒加载的原理onCreateView的时候Fragment有可能没有显示出来。<br>
 * 但是调用到setUserVisibleHint(boolean isVisibleToUser),isVisibleToUser =
 * true的时候就说明有显示出来<br>
 * 但是要考虑onCreateView和setUserVisibleHint的先后问题所以才有了下面的代码
 * <p>
 * 注意:<br>
 * 《1》原先的Fragment的回调方法名字后面要加个Lazy,比如Fragment的onCreateView方法, 就写成onCreateViewLazy <br>
 * 《2》使用该LazyFragment会导致多一层布局深度
 * <p>
 * LuckyJayce
 */
public class LazyFragment extends BaseFragment {
	private boolean isInit = false;
	private Bundle savedInstanceState;
	public static final String INTENT_BOOLEAN_LAZYLOAD = "intent_boolean_lazyLoad";
	private boolean isLazyLoad = true;
	private FrameLayout layout;

	@Deprecated
	protected final void onCreateView(Bundle savedInstanceState) {
		super.onCreateView(savedInstanceState);
		this.savedInstanceState = savedInstanceState;
		Bundle bundle = getArguments();
		if (bundle != null) {
			isLazyLoad = bundle.getBoolean(INTENT_BOOLEAN_LAZYLOAD, isLazyLoad);
		}
		//为什么不直接getUserVisibleHint();而是通过自己存isVisibleToUserState变量判断
		//因为v4的25的版本 已经调用 setUserVisibleHint(true),结果到这里getUserVisibleHint是false
		// (ps:看了FragmentManager源码Fragment被重新创建有直接赋值isVisibleToUser不知道是不是那里和之前v4有改动的地方)
		//所以我默认VISIBLE_STATE_NOTSET,之前没有调用setUserVisibleHint方法,就用系统的getUserVisibleHint,否则就用setUserVisibleHint后保存的值
		//总之就是调用了setUserVisibleHint 就使用setUserVisibleHint的值
		boolean isVisibleToUser;
		if (isVisibleToUserState == VISIBLE_STATE_NOTSET) {
			isVisibleToUser = getUserVisibleHint();
		} else {
			isVisibleToUser = isVisibleToUserState == VISIBLE_STATE_VISIABLE;
		}
		if (isLazyLoad) {
			if (isVisibleToUser && !isInit) {
				isInit = true;
				onCreateViewLazy(savedInstanceState);
			} else {
				LayoutInflater layoutInflater = inflater;
				if (layoutInflater == null) {
					layoutInflater = LayoutInflater.from(getApplicationContext());
				}
				layout = new FrameLayout(layoutInflater.getContext());
				View view = getPreviewLayout(layoutInflater, layout);
				if (view != null) {
					layout.addView(view);
				}
				layout.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
				super.setContentView(layout);
			}
		} else {
			isInit = true;
			onCreateViewLazy(savedInstanceState);
		}
	}

	private int isVisibleToUserState = VISIBLE_STATE_NOTSET;
	//未设置值
	private static final int VISIBLE_STATE_NOTSET = -1;
	//可见
	private static final int VISIBLE_STATE_VISIABLE = 1;
	//不可见
	private static final int VISIBLE_STATE_GONE = 0;

	@Override
	public void setUserVisibleHint(boolean isVisibleToUser) {
		super.setUserVisibleHint(isVisibleToUser);
		isVisibleToUserState = isVisibleToUser ? VISIBLE_STATE_VISIABLE : VISIBLE_STATE_GONE;
		if (isVisibleToUser && !isInit && getContentView() != null) {
			isInit = true;
			onCreateViewLazy(savedInstanceState);
			onResumeLazy();
		}
		if (isInit && getContentView() != null) {
			if (isVisibleToUser) {
				isStart = true;
				onFragmentStartLazy();
			} else {
				isStart = false;
				onFragmentStopLazy();
			}
		}
	}

	protected View getPreviewLayout(LayoutInflater inflater, ViewGroup container) {
		return null;
	}

	@Deprecated
	@Override
	public final void onStart() {
		super.onStart();
		if (isInit && !isStart && getUserVisibleHint()) {
			isStart = true;
			onFragmentStartLazy();
		}
	}

	@Deprecated
	@Override
	public final void onStop() {
		super.onStop();
		if (isInit && isStart && getUserVisibleHint()) {
			isStart = false;
			onFragmentStopLazy();
		}
	}

	private boolean isStart = false;

	protected void onFragmentStartLazy() {

	}

	protected void onFragmentStopLazy() {

	}

	protected void onCreateViewLazy(Bundle savedInstanceState) {

	}

	protected void onResumeLazy() {

	}

	protected void onPauseLazy() {

	}

	protected void onDestroyViewLazy() {

	}

	@Override
	public void setContentView(int layoutResID) {
		if (isLazyLoad && getContentView() != null && getContentView().getParent() != null) {
			layout.removeAllViews();
			View view = inflater.inflate(layoutResID, layout, false);
			layout.addView(view);
		} else {
			super.setContentView(layoutResID);
		}
	}

	@Override
	public void setContentView(View view) {
		if (isLazyLoad && getContentView() != null && getContentView().getParent() != null) {
			layout.removeAllViews();
			layout.addView(view);
		} else {
			super.setContentView(view);
		}
	}

	@Override
	@Deprecated
	public final void onResume() {
		super.onResume();
		if (isInit) {
			onResumeLazy();
		}
	}

	@Override
	@Deprecated
	public final void onPause() {
		super.onPause();
		if (isInit) {
			onPauseLazy();
		}
	}

	@Override
	@Deprecated
	public final void onDestroyView() {
		super.onDestroyView();
		if (isInit) {
			onDestroyViewLazy();
		}
		isInit = false;
	}
}



import java.lang.reflect.Field;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class BaseFragment extends Fragment {
	protected LayoutInflater inflater;
	private View contentView;
	private Context context;
	private ViewGroup container;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		context = getActivity().getApplicationContext();
	}

	@Override
	public final View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
		this.inflater = inflater;
		this.container = container;
		onCreateView(savedInstanceState);
		if (contentView == null)
			return super.onCreateView(inflater, container, savedInstanceState);
		return contentView;
	}

	protected void onCreateView(Bundle savedInstanceState) {

	}

	@Override
	public void onDestroyView() {
		super.onDestroyView();
		contentView = null;
		container = null;
		inflater = null;
	}

	public Context getApplicationContext() {
		return context;
	}

	public void setContentView(int layoutResID) {
		setContentView((ViewGroup) inflater.inflate(layoutResID, container, false));
	}

	public void setContentView(View view) {
		contentView = view;
	}

	public View getContentView() {
		return contentView;
	}

	public View findViewById(int id) {
		if (contentView != null)
			return contentView.findViewById(id);
		return null;
	}

	// http://stackoverflow.com/questions/15207305/getting-the-error-java-lang-illegalstateexception-activity-has-been-destroyed
	@Override
	public void onDetach() {
		super.onDetach();
		try {
			Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
			childFragmentManager.setAccessible(true);
			childFragmentManager.set(this, null);

		} catch (NoSuchFieldException e) {
			throw new RuntimeException(e);
		} catch (IllegalAccessException e) {
			throw new RuntimeException(e);
		}
	}

}

使用方法

public class ListFragment extends LazyFragment {

	@Override
	protected void onCreateViewLazy(Bundle savedInstanceState) {
		super.onCreateViewLazy(savedInstanceState);
		// 在这里进行初始化控件 findViewById
	}

	@Override
	protected void onResumeLazy() {
		super.onResumeLazy();
		// 在这里加载数据
	}

	@Override
	protected void onDestroyViewLazy() {
		super.onDestroyViewLazy();
		// 在这里进行对象的释放
	}
}
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