资源加载的流程

APP加载资源

我们APP中经常会用到图片，颜色等资源，但是你是否清楚这些资源是从什么时机，如何加载到我们的页面吗

加载思维导图

image.png

流程总结：

1.activtyThread的handerbindApplication开始，里面创建仪表盘，并调用Application的onCreate方法，调用loadedApk的makeApplication方法
2.这个方法中创建contextImpl类ContextImpl.createAppContext，这个里面调用contextImpl 的.setResources方法加载资源。资源参数是packageInfo.getResource（）
3.资源调用ResourcesManager.getInstance().getResources获取，里面调用createResources方法创建，findOrCreateResourcesImplForKeyLocked 里面再AssetManager assets = createAssetManager ，最后是通过setApkAssert调用native方法实现加载资源。

源码分析

1.入口和View创建在同一个类，ActivityThread中，handleBindApplication()开始，主要就三个核心点：1.创建Instrumentation对象,2，调用AppBindData.loadAPKInfo.makeApplication()创建Application，3再调用我们一般APP初始化的地方Application的onCreate方法

  /*  1.创建Instrumentation对象*/ 
    mInstrumentation = new Instrumentation();
            mInstrumentation.basicInit(this);
        }

    ...
 /*  2.创建application对象*/ 
            app = data.info.makeApplication(data.restrictedBackupMode, null);

            // Propagate autofill compat state
            app.setAutofillOptions(data.autofillOptions);

            // Propagate Content Capture options
            app.setContentCaptureOptions(data.contentCaptureOptions);

            mInitialApplication = app;

            // don't bring up providers in restricted mode; they may depend on the
            // app's custom Application class
            if (!data.restrictedBackupMode) {
                if (!ArrayUtils.isEmpty(data.providers)) {
                    installContentProviders(app, data.providers);
                }
            }

            // Do this after providers, since instrumentation tests generally start their
            // test thread at this point, and we don't want that racing.
            try {
                mInstrumentation.onCreate(data.instrumentationArgs);
            }
            catch (Exception e) {
                throw new RuntimeException(
                    "Exception thrown in onCreate() of "
                    + data.instrumentationName + ": " + e.toString(), e);
            }
            try {
 /*  3.通过Instrumentation对象调用Application的 onCreate方法*/ 
                mInstrumentation.callApplicationOnCreate(app);
            } catch (Exception e) {
                if (!mInstrumentation.onException(app, e)) {
                    throw new RuntimeException(
                      "Unable to create application " + app.getClass().getName()
                      + ": " + e.toString(), e);
                }
            }

2.上面方法2调用了

ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);

3.里面调用了createAppContext方法

static ContextImpl createAppContext(ActivityThread mainThread, LoadedApk packageInfo,
/**1，这里set资源*/
       context.setResources(packageInfo.getResources());
       context.mIsSystemOrSystemUiContext = isSystemOrSystemUI(context);
       return context;
   }

4.调用到getResouce方法

 public Resources getResources() {
       
            mResources = ResourcesManager.getInstance().getResources(null, mResDir,
                    splitPaths, mOverlayDirs, mApplicationInfo.sharedLibraryFiles,
                    Display.DEFAULT_DISPLAY, null, getCompatibilityInfo(),
                    getClassLoader(), null);
        }
        return mResources;
    }

5.又从LoadedApk方法，调到ResourcesManager.getInstance().getResources

public @Nullable Resources getResources(
            @Nullable IBinder activityToken,
            @Nullable String resDir,
            @Nullable String[] splitResDirs,
            @Nullable String[] overlayDirs,
            @Nullable String[] libDirs,
            int displayId,
            @Nullable Configuration overrideConfig,
            @NonNull CompatibilityInfo compatInfo,
            @Nullable ClassLoader classLoader,
            @Nullable List<ResourcesLoader> loaders) {
    ...

            return createResources(activityToken, key, classLoader);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
        }
    }

直接看createResources方法，里面调用了

private @Nullable Resources createResources(@Nullable IBinder activityToken,
            @NonNull ResourcesKey key, @NonNull ClassLoader classLoader) {
        synchronized (this) {
            if (DEBUG) {
                Throwable here = new Throwable();
                here.fillInStackTrace();
                Slog.w(TAG, "!! Get resources for activity=" + activityToken + " key=" + key, here);
            }

            ResourcesImpl resourcesImpl = findOrCreateResourcesImplForKeyLocked(key);
            if (resourcesImpl == null) {
                return null;
            }

            if (activityToken != null) {
                return createResourcesForActivityLocked(activityToken, classLoader,
                        resourcesImpl, key.mCompatInfo);
            } else {
                return createResourcesLocked(classLoader, resourcesImpl, key.mCompatInfo);
            }
        }
    }

看这个方法 findOrCreateResourcesImplForKeyLocked(key里面终于调用到 createResourcesImpl(key) ，这里就到咯Assert类类

private @Nullable ResourcesImpl createResourcesImpl(@NonNull ResourcesKey key) {
        final DisplayAdjustments daj = new DisplayAdjustments(key.mOverrideConfiguration);
        daj.setCompatibilityInfo(key.mCompatInfo);

        final AssetManager assets = createAssetManager(key);
        if (assets == null) {
            return null;
        }

        final DisplayMetrics dm = getDisplayMetrics(key.mDisplayId, daj);
        final Configuration config = generateConfig(key, dm);
        final ResourcesImpl impl = new ResourcesImpl(assets, dm, config, daj);

        if (DEBUG) {
            Slog.d(TAG, "- creating impl=" + impl + " with key: " + key);
        }
        return impl;
    }

再调用到加载资源到setApkAssets完成资源加载,调用native方法实现