a.java 文件源码

/**
 * A special variation to launch an activity only if a new activity
 * instance is needed to handle the given Intent.  In other words, this is
 * just like {@link #startActivityForResult(Intent, int)} except: if you are
 * using the {@link Intent#FLAG_ACTIVITY_SINGLE_TOP} flag, or
 * singleTask or singleTop
 * {@link android.R.styleable#AndroidManifestActivity_launchMode launchMode},
 * and the activity
 * that handles <var>intent</var> is the same as your currently running
 * activity, then a new instance is not needed.  In this case, instead of
 * the normal behavior of calling {@link #onNewIntent} this function will
 * return and you can handle the Intent yourself.
 *
 * <p>This function can only be called from a top-level activity; if it is
 * called from a child activity, a runtime exception will be thrown.
 *
 * @param intent The intent to start.
 * @param requestCode If >= 0, this code will be returned in
 *         onActivityResult() when the activity exits, as described in
 *         {@link #startActivityForResult}.
 * @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.
 *
 * @return If a new activity was launched then true is returned; otherwise
 *         false is returned and you must handle the Intent yourself.
 *
 * @see #startActivity
 * @see #startActivityForResult
 */
public boolean startActivityIfNeeded(@RequiresPermission @NonNull Intent intent,
                                     int requestCode, @Nullable Bundle options) {
    if (mParent == null) {
        int result = ActivityManager.START_RETURN_INTENT_TO_CALLER;
        try {
            Uri referrer = onProvideReferrer();
            if (referrer != null) {
                intent.putExtra(Intent.EXTRA_REFERRER, referrer);
            }
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(this);
            result = ActivityManagerNative.getDefault()
                    .startActivity(mMainThread.getApplicationThread(), getBasePackageName(),
                            intent, intent.resolveTypeIfNeeded(getContentResolver()), mToken,
                            mEmbeddedID, requestCode, ActivityManager.START_FLAG_ONLY_IF_NEEDED,
                            null, options);
        } catch (RemoteException e) {
            // Empty
        }

        Instrumentation.checkStartActivityResult(result, intent);

        if (requestCode >= 0) {
            // If this start is requesting a result, we can avoid making
            // the activity visible until the result is received.  Setting
            // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
            // activity hidden during this time, to avoid flickering.
            // This can only be done when a result is requested because
            // that guarantees we will get information back when the
            // activity is finished, no matter what happens to it.
            mStartedActivity = true;
        }
        return result != ActivityManager.START_RETURN_INTENT_TO_CALLER;
    }

    throw new UnsupportedOperationException(
            "startActivityIfNeeded can only be called from a top-level activity");
}