关于React Native 安卓首屏白屏优化

通过工具分析，问题主要在下面的代码上，

ReactRootView mReactRootView = createRootView(); mReactRootView.startReactApplication(mReactInstanceManager, getMainComponentName(), getLaunchOptions());

ReactActivity的onCreate()的完整代码如下：

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if (getUseDeveloperSupport() && Build.VERSION.SDK_INT >= 23) { // Get permission to show redbox in dev builds. if (!Settings.canDrawOverlays(this)) { Intent serviceIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION); startActivity(serviceIntent); FLog.w(ReactConstants.TAG, REDBOX_PERMISSION_MESSAGE); Toast.makeText(this, REDBOX_PERMISSION_MESSAGE, Toast.LENGTH_LONG).show(); } } mReactInstanceManager = createReactInstanceManager(); ReactRootView mReactRootView = createRootView(); mReactRootView.startReactApplication(mReactInstanceManager, getMainComponentName(), getLaunchOptions()); setContentView(mReactRootView); }

知道了产生问题的原因，我们就知道怎么着手优化了。我们首先想到的：-内存换时间

步骤一：

缓存rootview管理器主要用于初始化和缓存rootview对象。

import android.app.Activity; import android.os.Bundle; import android.view.ViewParent; import com.facebook.react.LifecycleState; import com.facebook.react.ReactInstanceManager; import com.facebook.react.ReactPackage; import com.facebook.react.ReactRootView; import java.lang.reflect.Field; /** * 缓存view管理 */ public class RNCacheViewManager { private static ReactRootView mRootView = null; private static ReactInstanceManager mManager = null; private static AbsRnInfo mRnInfo = null; //初始化 public static void init(Activity act, AbsRnInfo rnInfo) { init(act, rnInfo, null); } public static void init(Activity act, AbsRnInfo rnInfo, Bundle launchOptions) { if (mManager == null) { updateCache(act, rnInfo, launchOptions); } } public static void updateCache(Activity act, AbsRnInfo rnInfo) { updateCache(act, rnInfo, null); } //更新cache，适合于版本升级时候更新cache public static void updateCache(Activity act, AbsRnInfo rnInfo, Bundle launchOptions) { mRnInfo = rnInfo; mManager = createReactInstanceManager(act); mRootView = new ReactRootView(act); mRootView.startReactApplication(mManager, rnInfo.getMainComponentName(), launchOptions); } //设置模块名称，因为是private，只能通过反射赋值 public static void setModuleName(String moduleName) { try { Field field = ReactRootView.class.getDeclaredField("mJSModuleName"); field.setAccessible(true); field.set(getReactRootView(), moduleName); } catch (Throwable e) { throw new RuntimeException(e); } } //设置启动参数，因为是private，只能通过反射赋值 public static void setLaunchOptions(Bundle launchOptions) { try { Field field = ReactRootView.class.getDeclaredField("mLaunchOptions"); field.setAccessible(true); field.set(getReactRootView(), launchOptions); } catch (Throwable e) { throw new RuntimeException(e); } } public static ReactRootView getReactRootView() { if(mRootView==null){ throw new RuntimeException("缓存view管理器尚未初始化！"); } return mRootView; } public static ReactInstanceManager getReactInstanceManager() { if(mManager==null){ throw new RuntimeException("缓存view管理器尚未初始化！"); } return mManager; } public static AbsRnInfo getRnInfo() { if(mRnInfo==null){ throw new RuntimeException("缓存view管理器尚未初始化！"); } return mRnInfo; } public static void onDestroy() { try { ViewParent parent = getReactRootView().getParent(); if (parent != null) ((android.view.ViewGroup) parent).removeView(getReactRootView()); } catch (Throwable e) { e.printStackTrace(); } } public static void clear() { try { if (mManager != null) { mManager.onDestroy(); mManager = null; } if (mRootView != null) { onDestroy(); mRootView = null; } mRnInfo = null; } catch (Throwable e) { e.printStackTrace(); } } private static ReactInstanceManager createReactInstanceManager(Activity act) { ReactInstanceManager.Builder builder = ReactInstanceManager.builder() .setApplication(act.getApplication()) .setJSMainModuleName(getRnInfo().getJSMainModuleName()) .setUseDeveloperSupport(getRnInfo().getUseDeveloperSupport()) .setInitialLifecycleState(LifecycleState.BEFORE_RESUME); for (ReactPackage reactPackage : getRnInfo().getPackages()) { builder.addPackage(reactPackage); } String jsBundleFile = getRnInfo().getJSBundleFile(); if (jsBundleFile != null) { builder.setJSBundleFile(jsBundleFile); } else { builder.setBundleAssetName(getRnInfo().getBundleAssetName()); } return builder.build(); } }

步骤二

重写ReactActivity，可以拷贝出来改，也可以继承写，主要是重写onCreate和onDestroy，其余代码不动。onCreate方法中使用缓存rootview管理器来获得rootview对象，而不是重新创建。

onCreate()代码

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if (RNCacheViewManager.getRnInfo().getUseDeveloperSupport() && Build.VERSION.SDK_INT >= 23) { // Get permission to show redbox in dev builds. if (!Settings.canDrawOverlays(this)) { Intent serviceIntent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION); startActivity(serviceIntent); FLog.w(ReactConstants.TAG, REDBOX_PERMISSION_MESSAGE); Toast.makeText(this, REDBOX_PERMISSION_MESSAGE, Toast.LENGTH_LONG).show(); } } mReactInstanceManager = RNCacheViewManager.getReactInstanceManager(); ReactRootView mReactRootView = RNCacheViewManager.getReactRootView(); setContentView(mReactRootView); }

onDestroy方法中，不能再调用原有的mReactInstanceManager.destroy()方法了，否则rn初始化出来的对象会被销毁，下次就用不了了。同时，要卸载掉rootview的parent对象，否则下次再setContentView时候回报错。

protected void onDestroy() { RNCacheViewManager.onDestroy(); super.onDestroy(); }

RNCacheViewManager的onDeatory代码

public static void onDestroy() { try { ViewParent parent = getReactRootView().getParent(); if (parent != null) ((android.view.ViewGroup) parent).removeView(getReactRootView()); } catch (Throwable e) { e.printStackTrace(); } }

步骤三

在app启动时候初始化缓存rootview管理器。

RNCacheViewManager.init((Activity) context, new RnInfo(moduleName, launchOptions));

RnInfo实体类代码：

public class RnInfo extends AbsRnInfo { private String mModuleName; private Bundle mLaunchOptions; public RnInfo(String moduleName) { this.mModuleName = moduleName; } public RnInfo(String moduleName, Bundle launchOptions) { this.mModuleName = moduleName; this.mLaunchOptions = launchOptions; } @Nullable @Override public Bundle getLaunchOptions() { return mLaunchOptions; } @Override public String getMainComponentName() { return mModuleName; } @Override public String getJSMainModuleName() { return RNKeys.Default.DEf_JS_MAIN_MODULE_NAME; } @Nullable @Override public String getJSBundleFile() { return RNManager.getJsBundlePath(); } @Override public boolean getUseDeveloperSupport() { return true; } @Override public List<ReactPackage> getPackages() { return Arrays.asList( new MainReactPackage(), new BBReactPackage() ); } }