Chrome自定义标签：为什么CustomTabsClient.bindCustomTabsService（）无法正常运行？

我正在尝试实现chrome自定义标签，但遇到以下运行时错误：

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nirvan.customtabsexample/com.example.nirvan.customtabsexample.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.customtabs.CustomTabsClient.warmup(long)' on a null object reference

这是我的代码：

 CustomTabsClient mClient;
    String packageName = "com.android.chrome";

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


        // Binds to the service.
        CustomTabsClient.bindCustomTabsService(this, packageName, new CustomTabsServiceConnection() {
            @Override
            public void onCustomTabsServiceConnected(ComponentName name, CustomTabsClient client) {
                // mClient is now valid.
                Log.e("TAG","onCustumServiceConnected");
                mClient = client;
            }

            @Override
            public void onServiceDisconnected(ComponentName name) {
                // mClient is no longer valid. This also invalidates sessions.
                Log.e("TAG","onServiceDisconnected");
                mClient = null;
            }
        });


        mClient.warmup(0);


        CustomTabsSession session = mClient.newSession(new CustomTabsCallback());
        session.mayLaunchUrl(Uri.parse("https://www.google.com"), null, null);


        Button button=(Button)findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String url = "https://www.facebook.com/";
                CustomTabsIntent.Builder builder = new CustomTabsIntent.Builder();
                CustomTabsIntent customTabsIntent = builder.build();
                customTabsIntent.launchUrl(MainActivity.this, Uri.parse(url));
            }
        });






    }

该应用程序一启动就会崩溃。另外，我没有获得2个日志输出中的任何一个，因此CustomTabsClient.bindCustomTabsService()永远不会调用下面的两个方法。可能是什么问题？我认为这是我要传递给的软件包名称CustomTabsClient.bindCustomTabsService()。我不知道要通过什么，所以我通过了"com.android.chrome"。这是什么问题吗？

您NullPointerException在以下行得到一个：

mClient.warmup(0);

这样做的原因是，一旦调用CustomTabsClient.bindCustomTabsService，回调将异步运行。发生预热调用时，服务没有足够的时间连接并为分配一个值mClient。将预热调用和mayLaunchUrl移到onConnected回调内部，它应该可以工作。

    // Binds to the service.
    CustomTabsClient.bindCustomTabsService(this, packageName, new CustomTabsServiceConnection() {
        @Override
        public void onCustomTabsServiceConnected(ComponentName name, CustomTabsClient client) {
            // mClient is now valid.
            Log.e("TAG","onCustomTabsServiceConnected");
            mClient = client;
            mClient.warmup(0);
            CustomTabsSession session = mClient.newSession(new CustomTabsCallback());
            session.mayLaunchUrl(Uri.parse("https://www.google.com"), null, null);

        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            // mClient is no longer valid. This also invalidates sessions.
            Log.e("TAG","onServiceDisconnected");
            mClient = null;
        }
    });