我正在研究您Navigation Drawer Activity在 Android Studio 中启动时生成的示例代码。我想做的是以编程方式更改包含的视图，我的研究表明 ViewStub 是最好的方法。但是我无法让它工作。对于有问题的主要布局，涉及 3 个文件：
活动主.xml：
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="@layout/app_bar_main"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer" />
</android.support.v4.widget.DrawerLayout>
app_bar_main.xml：
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.MY_APP.android.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<ViewStub
android:id="@+id/main_content"
android:inflatedId="@id/main_content"
android:layout="@layout/content_main"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email" />
</android.support.design.widget.CoordinatorLayout>
content_main.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/app_bar_main"
tools:context="com.MY_APP.android.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/content_textview"
android:text="//TODO Main Feed"/>
</RelativeLayout>
以下是我的 MainActivity.java。似乎什么都没有发生，并且 content_main 似乎从未出现过。这可能是可见性问题吗？
package com.myapp.android;
import android.app.Dialog;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.view.ViewStub;
import android.widget.Toast;
import com.facebook.FacebookSdk;
import com.facebook.login.LoginManager;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
public class MainActivity
extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
NetworkHelpers NetworkHelper = new NetworkHelpers();
SharedPreferences sharedpreferences;
@Override
protected void onCreate(Bundle savedInstanceState) {
//Check if user is connected
if(!NetworkHelper.checkConnectivity(this)){
NetworkHelper.showNotConnectedAlert(this);
}
//Check for Google Play Services
checkGooglePlayServicesAvailable();
//Get User Info From Database
sharedpreferences = getSharedPreferences("com.myapp.android.prefs", Context.MODE_PRIVATE);
String login_token = sharedpreferences.getString("login_token", "");
String first_name = sharedpreferences.getString("first_name", "");
String last_name = sharedpreferences.getString("last_name", "");
String email = sharedpreferences.getString("email", "");
if (login_token.isEmpty()){
//Start LoginActivity
Intent intent = new Intent(this, LoginActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
finish();
startActivity(intent);
}else{
//Update user info
ArrayList<String> params = new ArrayList<String>();
params.add(login_token);
new getUserInfo().execute(params);
}
//Create View
super.onCreate(savedInstanceState);
setContentView(com.myapp.android.R.layout.activity_main);
//Set Toolbar and Navigation Drawer
Toolbar toolbar = (Toolbar) findViewById(com.myapp.android.R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(com.myapp.android.R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, com.myapp.android.R.string.navigation_drawer_open, com.myapp.android.R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(com.myapp.android.R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
ViewStub stub = (ViewStub) findViewById(R.id.main_content);
stub.setLayoutResource(R.layout.content_main);
stub.inflate();
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(com.myapp.android.R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.nav_home) {
// Start Home Screen
} else if (id == R.id.nav_videos) {
// Start Videos Screen
} else if (id == R.id.nav_photos) {
// Start Photos Screen
} else if (id == R.id.nav_galleries) {
// Start Galleries Screen
} else if (id == R.id.nav_map) {
// Start Map Screen
} else if (id == com.myapp.android.R.id.nav_share) {
//Open share app dialog
Intent intent = new Intent(Intent.ACTION_SEND);
intent.setType("text/plain");
intent.putExtra(Intent.EXTRA_SUBJECT, "My App");
intent.putExtra(Intent.EXTRA_TEXT, "Check out My App: http://myapp.com/app");
Intent chooser = Intent.createChooser(intent, "Tell a friend about My App");
startActivity(chooser);
} else if (id == com.myapp.android.R.id.nav_logout){
logout();
}
DrawerLayout drawer = (DrawerLayout) findViewById(com.myapp.android.R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
//AsyncTask to get user info from api
class getUserInfo extends AsyncTask<ArrayList<String>, Void, String> {
@Override
protected String doInBackground(ArrayList<String>... params) {
String token = params[0].get(0);
String response = HttpRequest.post("http://api.myapp.com/users/get-info/").send("api_key=API_KEY&token="+token).body();
return response;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected void onPostExecute(String result) {
try {
// Do JSON Stuff
JSONObject jsonobject = new JSONObject(result);
String status = jsonobject.get("status").toString();
String message = jsonobject.get("message").toString();
JSONObject userinfo = jsonobject.getJSONObject("user_info");
//Set up user variables
String first_name = userinfo.get("first_name").toString();
String last_name = userinfo.get("last_name").toString();
String email = userinfo.get("email").toString();
String display_name = userinfo.get("display_name").toString();
String about = userinfo.get("about").toString();
String newsletter = userinfo.get("newsletter").toString();
if (status.equals("success")){
updateSharedPreferences(first_name, last_name, email, display_name, about, newsletter);
}else if (status.equals("error")){
logout();
} else{
logout();
}
} catch (JSONException e) {
Toast.makeText(getApplicationContext(),"An unknown error occurred.", Toast.LENGTH_SHORT).show();
logout();
}
}
}
private boolean checkGooglePlayServicesAvailable() {
final int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getApplicationContext());
if (status == ConnectionResult.SUCCESS) {
return true;
}
if (GooglePlayServicesUtil.isUserRecoverableError(status)) {
final Dialog errorDialog = GooglePlayServicesUtil.getErrorDialog(status, this, 1);
if (errorDialog != null)
{
errorDialog.show();
}
}
return false;
}
private void updateSharedPreferences(String first_name, String last_name, String email, String display_name, String about, String newsletter){
//Put user info into sharedpreferences
SharedPreferences sharedpreferences = getSharedPreferences("com.myapp.android.prefs", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedpreferences.edit();
editor.putString("first_name", first_name);
editor.putString("last_name", last_name);
editor.putString("email", email);
editor.putString("display_name", display_name);
editor.putString("about", about);
editor.putString("newsletter", newsletter);
editor.commit();
}
private void logout(){
//Logout of Facebook
FacebookSdk.sdkInitialize(this);
LoginManager.getInstance().logOut();
//Unset shared preferences login token
SharedPreferences sharedpreferences = getSharedPreferences("com.myapp.android.prefs", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedpreferences.edit();
editor.putString("login_token", "");
editor.putString("facebook_token", "");
editor.putString("google_token", "");
editor.commit();
//Open login screen
Intent intent = new Intent(getApplicationContext(), LoginActivity.class);
finish();
startActivity(intent);
}
}