• 主要分析startActivityForResult以后Fragment中onActivityResult回調(diào)回來(lái)的邏輯

• android.app.Fragment 類中有這么一個(gè)方法，這里會(huì)去調(diào)用mHost中的onStartActivityFromFragment，所以這里來(lái)看看mHost是什么鬼？

/**
     * Call {@link Activity#startActivityForResult(Intent, int, Bundle)} from the fragment's
     * containing Activity.
     */
    public void startActivityForResult(Intent intent, int requestCode, Bundle options) {
        if (mHost == null) {
            throw new IllegalStateException("Fragment " + this + " not attached to Activity");
        }
        mHost.onStartActivityFromFragment(this, intent, requestCode, options);
    }

android.app.Fragment 類中有這么一個(gè)Callback，這個(gè)Callback是android.app.FragmentHostCallback的一個(gè)實(shí)例，從這個(gè)類的注釋中看到，F(xiàn)ragment肯定是有宿主的，正如Activity中去開啟一個(gè)Fragment，這個(gè)Activity就是Fragment的宿主了，這個(gè)Callback就是用來(lái)回調(diào)宿主中的一些方法的。

// Activity this fragment is attached to.
    FragmentHostCallback mHost;

看這個(gè)android.app.FragmentHostCallback的一個(gè)方法，最終會(huì)調(diào)用startActivity，這個(gè)很明顯就是Activity中的方法，所以確定了這個(gè)類的作用以后，會(huì)更加的清晰我們繼續(xù)分析下去的流程。

/**
     * Starts a new {@link Activity} from the given fragment.
     * See {@link Activity#startActivityForResult(Intent, int)}.
     */
    public void onStartActivityFromFragment(Fragment fragment, Intent intent, int requestCode,
            Bundle options) {
        if (requestCode != -1) {
            throw new IllegalStateException(
                    "Starting activity with a requestCode requires a FragmentActivity host");
        }
        mContext.startActivity(intent);
    }

其實(shí)上面的方法不是真正的執(zhí)行流程， Activity中有HostCallbacks這個(gè)東西里面重寫了上面onStartActivityFromFragment方法

class HostCallbacks extends FragmentHostCallback<Activity> {
        public HostCallbacks() {
            super(Activity.this /*activity*/);
        }

       ...省略一些不必要的方法
        @Override
        public void onStartActivityFromFragment(Fragment fragment, Intent intent, int requestCode,
                Bundle options) {
            //這里就是重寫了的方法，重點(diǎn)分析startActivityFromFragment
            Activity.this.startActivityFromFragment(fragment, intent, requestCode, options);
        }
...省略一些不必要的方法

下面就是startActivityFromFragment的主要邏輯

/**
     * This is called when a Fragment in this activity calls its
     * {@link Fragment#startActivity} or {@link Fragment#startActivityForResult}
     * method.
     *
     * <p>This method throws {@link android.content.ActivityNotFoundException}
     * if there was no Activity found to run the given Intent.
     *
     * @param fragment The fragment making the call.
     * @param intent The intent to start.
     * @param requestCode Reply request code.  < 0 if reply is not requested.
     * @param options Additional options for how the Activity should be started.
     * See {@link android.content.Context#startActivity(Intent, Bundle)
     * Context.startActivity(Intent, Bundle)} for more details.
     *
     * @throws android.content.ActivityNotFoundException
     *
     * @see Fragment#startActivity
     * @see Fragment#startActivityForResult
     */
    public void startActivityFromFragment(@NonNull Fragment fragment,
            @RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
        startActivityForResult(fragment.mWho, intent, requestCode, options);
    }

    /**
     * @hide
     */
    @Override
    public void startActivityForResult(
            String who, Intent intent, int requestCode, @Nullable Bundle options) {
        Uri referrer = onProvideReferrer();
        if (referrer != null) {
            intent.putExtra(Intent.EXTRA_REFERRER, referrer);
        }
        options = transferSpringboardActivityOptions(options);
        Instrumentation.ActivityResult ar =
            mInstrumentation.execStartActivity(
                this, mMainThread.getApplicationThread(), mToken, who,
                intent, requestCode, options);
        if (ar != null) {
            mMainThread.sendActivityResult(
                mToken, who, requestCode,
                ar.getResultCode(), ar.getResultData());
        }
        cancelInputsAndStartExitTransition(options);
    }