Quantcast
Channel: CSDN博客移动开发推荐文章
Viewing all articles
Browse latest Browse all 5930

最新版本React Native实现JsBundle预加载,界面秒开优化

$
0
0

前些时间和大家分享了一系列关于React Native For Android的文章。这两天又对React Native增量热更新的博客进行了填充,增加了图片增量更新的实现方案和过程。有兴趣的朋友可以去浏览详细内容。为了方便,我将前几篇的博客链接贴出来供大家参考:


Android原生项目集成React Native


React Native与Android通信交互


React Native 实现热部署、差异化增量热更新


React Native开源项目 「漫画书」


一、问题分析


本篇博客同样和大家分享关于React Native的内容。想必大家在撸码中都发现了一个问题:从Android原生界面第一次跳转到React Native界面时,界面会有短暂的白屏过程,然后才会加载出界面。下次再跳转就不会出现这种问题。并且当我们杀死App,重新从Android Activity跳转到RN界面时,仍然会出现短暂白屏。

为什么第一次加载React Native界面会出现短暂白屏呢?大家别忘了,React Native的渲染机制是对于JsBundle的加载。项目中所有的js文件最终会被打包成一个JsBundle文件中,Android中为:‘index.android.bundle’。系统在第一次渲染界面时,会首先加载JsBundle文件。那么问题肯定出现在加载JsBundle这个过程,即出现白屏可能是因为JsBundle正在加载。发现了原因,我们继续查看源码,看看是否能从源码中得知一二。


二、源码分析


Android集成的RN界面,需要继承ReactActivity,那么直接从ReactActivity源码入手:

public abstract class ReactActivity extends Activity
    implements DefaultHardwareBackBtnHandler, PermissionAwareActivity {

  private final ReactActivityDelegate mDelegate;

  protected ReactActivity() {
    mDelegate = createReactActivityDelegate();
  }

  /**
   * Returns the name of the main component registered from JavaScript.
   * This is used to schedule rendering of the component.
   * e.g. "MoviesApp"
   */
  protected @Nullable String getMainComponentName() {
    return null;
  }

  /**
   * Called at construction time, override if you have a custom delegate implementation.
   */
  protected ReactActivityDelegate createReactActivityDelegate() {
    return new ReactActivityDelegate(this, getMainComponentName());
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mDelegate.onCreate(savedInstanceState);
  }

  @Override
  protected void onPause() {
    super.onPause();
    mDelegate.onPause();
  }

  @Override
  protected void onResume() {
    super.onResume();
    mDelegate.onResume();
  }

  @Override
  protected void onDestroy() {
    super.onDestroy();
    mDelegate.onDestroy();
  }
  // 其余代码略......
}
不难发现,ReactActivity中的行为都交给了ReactActivityDelegate类来处理。很明显是委托模式。至于白屏原因是因为第一次创建时,那么我们直接看onCreate即可。找到ReactActivityDelegate的onCreate方法:

protected void onCreate(Bundle savedInstanceState) {
    boolean needsOverlayPermission = false;
    if (getReactNativeHost().getUseDeveloperSupport() && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
      // Get permission to show redbox in dev builds.
      if (!Settings.canDrawOverlays(getContext())) {
        needsOverlayPermission = true;
        Intent serviceIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + getContext().getPackageName()));
        FLog.w(ReactConstants.TAG, REDBOX_PERMISSION_MESSAGE);
        Toast.makeText(getContext(), REDBOX_PERMISSION_MESSAGE, Toast.LENGTH_LONG).show();
        ((Activity) getContext()).startActivityForResult(serviceIntent, REQUEST_OVERLAY_PERMISSION_CODE);
      }
    }

    if (mMainComponentName != null && !needsOverlayPermission) {
      loadApp(mMainComponentName);
    }
    mDoubleTapReloadRecognizer = new DoubleTapReloadRecognizer();
  }
从源码可以看到,最终调用了loadApp方法,继续跟踪loadApp方法:

  protected void loadApp(String appKey) {
    if (mReactRootView != null) {
      throw new IllegalStateException("Cannot loadApp while app is already running.");
    }
    mReactRootView = createRootView();
    mReactRootView.startReactApplication(
      getReactNativeHost().getReactInstanceManager(),
      appKey,
      getLaunchOptions());
    getPlainActivity().setContentView(mReactRootView);
  }
 protected ReactRootView createRootView() {
    return new ReactRootView(getContext());
  }

loadApp方法中调用了createRootView创建了ReactRootView,即React Native界面,并且将界面设置到Activity中。那么问题很可能出现在这了。插个断点,调试看看执行时间。

一切恍然大悟,在createRootView和startReactApplication时,消耗了较长时间。

既然是createRootView和startReactApplication执行了耗时操作的问题,那么我们只需要将其提前执行,创建出ReactRootView并缓存下来。当跳转到React Native界面时,直接设置到ContentView即可。有了解决思路,又该到我们甩起袖子撸码了。


三、功能实现


/**
 * 预加载工具类
 * Created by Song on 2017/5/10.
 */
public class ReactNativePreLoader {

    private static final Map<String,ReactRootView> CACHE = new ArrayMap<>();

    /**
     * 初始化ReactRootView,并添加到缓存
     * @param activity
     * @param componentName
     */
    public static void preLoad(Activity activity, String componentName) {

        if (CACHE.get(componentName) != null) {
            return;
        }
        // 1.创建ReactRootView
        ReactRootView rootView = new ReactRootView(activity);
        rootView.startReactApplication(
                ((ReactApplication) activity.getApplication()).getReactNativeHost().getReactInstanceManager(),
                componentName,
                null);

        // 2.添加到缓存
        CACHE.put(componentName, rootView);
    }

    /**
     * 获取ReactRootView
     * @param componentName
     * @return
     */
    public static ReactRootView getReactRootView(String componentName) {
        return CACHE.get(componentName);
    }

    /**
     * 从当前界面移除 ReactRootView
     * @param component
     */
    public static void deatchView(String component) {
        try {
            ReactRootView rootView = getReactRootView(component);
            ViewGroup parent = (ViewGroup) rootView.getParent();
            if (parent != null) {
                parent.removeView(rootView);
            }
        } catch (Throwable e) {
            Log.e("ReactNativePreLoader",e.getMessage());
        }
    }

上述代码很简单,包含了三个方法:

(1)preLoad

         负责创建ReactRootView,并添加到缓存。

(2)getReactRootView

        获取创建的RootView

(3)deatchView

        将添加的RootView从布局根容器中移除,在 ReactActivity 销毁后,我们需要把 view 从 parent 上卸载下来,避免出现重复添加View的异常。

从源码分析部分我们知道,集成React Native界面时,只需要继承ReactActivity,并实现getMainComponentName方法即可。加载创建视图的流程系统都在ReactActivity帮我们完成。现在因为自定义了ReactRootView的加载方式,要使用预加载方式,就不能直接继承ReactActivity。所以接下来需要我们自定义ReactActivity。

从源码中我们已经发现,ReactActivity的处理都交给了ReactActivityDelegate。所以我们可以自定义一个新的ReactActivityDelegate,只需要修改onCreate创建部分,其他照搬源码即可。

public class PreLoadReactDelegate {

    private final Activity mActivity;
    private ReactRootView mReactRootView;
    private Callback mPermissionsCallback;
    private final String mMainComponentName;
    private PermissionListener mPermissionListener;
    private final int REQUEST_OVERLAY_PERMISSION_CODE = 1111;
    private DoubleTapReloadRecognizer mDoubleTapReloadRecognizer;

    public PreLoadReactDelegate(Activity activity, @Nullable String mainComponentName) {
        this.mActivity = activity;
        this.mMainComponentName = mainComponentName;
    }

    public void onCreate() {
        boolean needsOverlayPermission = false;
        if (getReactNativeHost().getUseDeveloperSupport() && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // Get permission to show redbox in dev builds.
            if (!Settings.canDrawOverlays(mActivity)) {
                needsOverlayPermission = true;
                Intent serviceIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + mActivity.getPackageName()));
                mActivity.startActivityForResult(serviceIntent, REQUEST_OVERLAY_PERMISSION_CODE);
            }
        }

        if (mMainComponentName != null && !needsOverlayPermission) {
            // 1.从缓存中获取RootView
            mReactRootView = ReactNativePreLoader.getReactRootView(mMainComponentName);

            if(mReactRootView == null) {

                // 2.缓存中不存在RootView,直接创建
                mReactRootView = new ReactRootView(mActivity);
                mReactRootView.startReactApplication(
                        getReactInstanceManager(),
                        mMainComponentName,
                        null);
            }
            // 3.将RootView设置到Activity布局
            mActivity.setContentView(mReactRootView);
        }

        mDoubleTapReloadRecognizer = new DoubleTapReloadRecognizer();
    }

    public void onResume() {
        if (getReactNativeHost().hasInstance()) {
            getReactInstanceManager().onHostResume(mActivity, (DefaultHardwareBackBtnHandler)mActivity);
        }
        if (mPermissionsCallback != null) {
            mPermissionsCallback.invoke();
            mPermissionsCallback = null;
        }
    }

    public void onPause() {
        if (getReactNativeHost().hasInstance()) {
            getReactInstanceManager().onHostPause(mActivity);
        }
    }

    public void onDestroy() {

        if (mReactRootView != null) {
            mReactRootView.unmountReactApplication();
            mReactRootView = null;
        }
        if (getReactNativeHost().hasInstance()) {
            getReactInstanceManager().onHostDestroy(mActivity);
        }

        // 清除View
        ReactNativePreLoader.deatchView(mMainComponentName);
    }

    public boolean onNewIntent(Intent intent) {
        if (getReactNativeHost().hasInstance()) {
            getReactInstanceManager().onNewIntent(intent);
            return true;
        }
        return false;
    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (getReactNativeHost().hasInstance()) {
            getReactInstanceManager().onActivityResult(mActivity, requestCode, resultCode, data);
        } else {
            // Did we request overlay permissions?
            if (requestCode == REQUEST_OVERLAY_PERMISSION_CODE && Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                if (Settings.canDrawOverlays(mActivity)) {
                    if (mMainComponentName != null) {
                        if (mReactRootView != null) {
                            throw new IllegalStateException("Cannot loadApp while app is already running.");
                        }
                        mReactRootView = new ReactRootView(mActivity);
                        mReactRootView.startReactApplication(
                                getReactInstanceManager(),
                                mMainComponentName,
                                null);
                        mActivity.setContentView(mReactRootView);
                    }
                }
            }
        }
    }

    public boolean onBackPressed() {
        if (getReactNativeHost().hasInstance()) {
            getReactInstanceManager().onBackPressed();
            return true;
        }
        return false;
    }

    public boolean onRNKeyUp(int keyCode) {
        if (getReactNativeHost().hasInstance() && getReactNativeHost().getUseDeveloperSupport()) {
            if (keyCode == KeyEvent.KEYCODE_MENU) {
                getReactInstanceManager().showDevOptionsDialog();
                return true;
            }
            boolean didDoubleTapR = Assertions.assertNotNull(mDoubleTapReloadRecognizer)
                    .didDoubleTapR(keyCode, mActivity.getCurrentFocus());
            if (didDoubleTapR) {
                getReactInstanceManager().getDevSupportManager().handleReloadJS();
                return true;
            }
        }
        return false;
    }

    public void requestPermissions(String[] permissions, int requestCode, PermissionListener listener) {
        mPermissionListener = listener;
        mActivity.requestPermissions(permissions, requestCode);
    }

    public void onRequestPermissionsResult(final int requestCode, final String[] permissions, final int[] grantResults) {
        mPermissionsCallback = new Callback() {
            @Override
            public void invoke(Object... args) {
                if (mPermissionListener != null && mPermissionListener.onRequestPermissionsResult(requestCode, permissions, grantResults)) {
                    mPermissionListener = null;
                }
            }
        };
    }

    /**
     * 获取 Application中 ReactNativeHost
     * @return
     */
    private ReactNativeHost getReactNativeHost() {
        return MainApplication.getInstance().getReactNativeHost();
    }

    /**
     * 获取 ReactInstanceManager
     * @return
     */
    private ReactInstanceManager getReactInstanceManager() {
        return getReactNativeHost().getReactInstanceManager();
    }
}

代码很长,重点在onCreate方法:

 if (mMainComponentName != null && !needsOverlayPermission) {
            // 1.从缓存中获取RootView
            mReactRootView = ReactNativePreLoader.getReactRootView(mMainComponentName);

            if(mReactRootView == null) {

                // 2.缓存中不存在RootView,直接创建
                mReactRootView = new ReactRootView(mActivity);
                mReactRootView.startReactApplication(
                        getReactInstanceManager(),
                        mMainComponentName,
                        null);
            }
            // 3.将RootView设置到Activity布局
            mActivity.setContentView(mReactRootView);
        }
(1)首先从缓存中取ReactRootView

(2)缓存中不存在ReactRootView,直接创建。此时和系统帮我们创建ReactRootView没有区别

(3)将ReactRootView设置到Activity布局

很明显,我们让加载流程先经过缓存,如果缓存中已经存在了RootView,那么就可以直接设置到Activity布局,如果缓存中不存在,再去执行创建过程。

ReactNativePreLoader.preLoad(this,"HotRN");

我们在启动React Native前一个界面,执行preLoad方法优先加载出ReactRootView,此时就完成了视图预加载,让React Native界面达到秒显的效果。


四、效果对比


Ok,到此想必大家都想撸起袖子体验一下了,那就开始吧~~ 源码已分享到Github,别忘了给颗star哦吐舌头~

点击查看源码



作者:u013718120 发表于2017/5/10 16:48:09 原文链接
阅读:70 评论:0 查看评论

Viewing all articles
Browse latest Browse all 5930

Trending Articles



<script src="https://jsc.adskeeper.com/r/s/rssing.com.1596347.js" async> </script>