<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <TextView
        android:id="@+id/main_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="18sp"
        android:layout_centerInParent="true"
        />

</RelativeLayout>

public class MainActivity extends AppCompatActivity {

    private TextView main_tv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        main_tv = (TextView) findViewById(R.id.main_tv);

        new Thread(new Runnable() {

            @Override
            public void run() {
                main_tv.setText("子线程中访问");
            }
        }).start();

    }

}

public class MainActivity extends AppCompatActivity {

    private TextView main_tv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        main_tv = (TextView) findViewById(R.id.main_tv);

        new Thread(new Runnable() {

            @Override
            public void run() {
                try {
                    Thread.sleep(200);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                main_tv.setText("子线程中访问");
            }
        }).start();

    }

}

void checkThread() {
    if (mThread != Thread.currentThread()) {
        throw new CalledFromWrongThreadException(
                "Only the original thread that created a view hierarchy can touch its views.");
    }
}

@Override
public void requestLayout() {
    if (!mHandlingLayoutInLayoutRequest) {
        checkThread();
        mLayoutRequested = true;
        scheduleTraversals();
    }
}

void scheduleTraversals() {
    if (!mTraversalScheduled) {
        mTraversalScheduled = true;
        mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
        mChoreographer.postCallback(
                Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
        if (!mUnbufferedInputDispatch) {
            scheduleConsumeBatchedInput();
        }
        notifyRendererOfFramePending();
        pokeDrawLockIfNeeded();
    }
}

final class TraversalRunnable implements Runnable {
    @Override
    public void run() {
        doTraversal();
    }
}

void doTraversal() {
    if (mTraversalScheduled) {
        mTraversalScheduled = false;
        mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

        if (mProfile) {
            Debug.startMethodTracing("ViewAncestor");
        }

        performTraversals();

        if (mProfile) {
            Debug.stopMethodTracing();
            mProfile = false;
        }
    }
}

final void handleResumeActivity(IBinder token,
        boolean clearHide, boolean isForward, boolean reallyResume) {
    // If we are getting ready to gc after going to the background, well
    // we are back active so skip it.
    unscheduleGcIdler();
    mSomeActivitiesChanged = true;

    // TODO Push resumeArgs into the activity for consideration
    ActivityClientRecord r = performResumeActivity(token, clearHide);

    if (r != null) {
        final Activity a = r.activity;

        //代码省略

            r.activity.mVisibleFromServer = true;
            mNumVisibleActivities++;
            if (r.activity.mVisibleFromClient) {
                r.activity.makeVisible();
            }
        }

      //代码省略    
}

public final ActivityClientRecord performResumeActivity(IBinder token,
        boolean clearHide) {
    ActivityClientRecord r = mActivities.get(token);
    if (localLOGV) Slog.v(TAG, "Performing resume of " + r
            + " finished=" + r.activity.mFinished);
    if (r != null && !r.activity.mFinished) {
    //代码省略
            r.activity.performResume();

    //代码省略

    return r;
}

final void performResume() {
    performRestart();

    mFragments.execPendingActions();

    mLastNonConfigurationInstances = null;

    mCalled = false;
    // mResumed is set by the instrumentation
    mInstrumentation.callActivityOnResume(this);

    //代码省略

}

public void callActivityOnResume(Activity activity) {
    activity.mResumed = true;
    activity.onResume();

    if (mActivityMonitors != null) {
        synchronized (mSync) {
            final int N = mActivityMonitors.size();
            for (int i=0; i<N; i++) {
                final ActivityMonitor am = mActivityMonitors.get(i);
                am.match(activity, activity, activity.getIntent());
            }
        }
    }
}

r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
    r.activity.makeVisible();
}

void makeVisible() {
    if (!mWindowAdded) {
        ViewManager wm = getWindowManager();
        wm.addView(mDecor, getWindow().getAttributes());
        mWindowAdded = true;
    }
    mDecor.setVisibility(View.VISIBLE);
}

@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mDisplay, mParentWindow);
}

public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {

    //代码省略  


    ViewRootImpl root;
    View panelParentView = null;

    //代码省略

        root = new ViewRootImpl(view.getContext(), display);

        view.setLayoutParams(wparams);

        mViews.add(view);
        mRoots.add(root);
        mParams.add(wparams);
    }

    // do this last because it fires off messages to start doing things
    try {
        root.setView(view, wparams, panelParentView);
    } catch (RuntimeException e) {
        // BadTokenException or InvalidDisplayException, clean up.
        synchronized (mLock) {
            final int index = findViewLocked(view, false);
            if (index >= 0) {
                removeViewLocked(index, true);
            }
        }
        throw e;
    }
}