Android OnClick和OnclickListner

时间：2017-07-19 07:34:43

标签： java android

我是Android开发的新手。我当前的应用程序崩溃了来自XML的onClick事件，但它似乎与onClickListner一起正常工作。

public static String URL_WEB;     NsdUtils mNsdUtils; 

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

    final NsdUtils mNsdUtils = new NsdUtils(this);
    mNsdUtils.initializeNsd();
    /*Button button =(Button) findViewById(R.id.btn_discover_networks);

    button.setOnClickListener(new View.OnClickListener(){
        public void onClick(View view)
        {
            mNsdUtils.discoverServices();
        }
    });*/
}

public void onClickDiscover(View view){
    mNsdUtils.discoverServices();
}

日志：

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.android.implicitintents, PID: 6397
                  java.lang.IllegalStateException: Could not execute method for android:onClick
                      at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
                      at android.view.View.performClick(View.java:5637)
                      at android.view.View$PerformClick.run(View.java:22429)
                      at android.os.Handler.handleCallback(Handler.java:751)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6119)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                   Caused by: java.lang.reflect.InvocationTargetException
                      at java.lang.reflect.Method.invoke(Native Method)
                      at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
                      at android.view.View.performClick(View.java:5637) 
                      at android.view.View$PerformClick.run(View.java:22429) 
                      at android.os.Handler.handleCallback(Handler.java:751) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6119) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.android.implicitintents.Utils.NsdUtils.discoverServices()' on a null object reference
                      at com.example.android.implicitintents.MainActivity.onClickDiscoverAura(MainActivity.java:40)
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
                      at android.view.View.performClick(View.java:5637) 
                      at android.view.View$PerformClick.run(View.java:22429) 
                      at android.os.Handler.handleCallback(Handler.java:751) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6119) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

我似乎错过了一个非常基本的细节。任何帮助都会很棒。

NsdUtils 

public class NsdUtils {
    Context mContext;

    NsdManager mNsdManager;
    NsdManager.ResolveListener mResolveListener;
    NsdManager.DiscoveryListener mDiscoveryListener;


    //To find all the available networks SERVICE_TYPE = "_services._dns-sd._udp"
    public static final String SERVICE_TYPE = "_http._tcp";

    public static final String TAG = "NsdUtils";
    public String mServiceName = "_hap";

    NsdServiceInfo mService;

    public NsdUtils(Context context) {
        mContext = context;
        mNsdManager = (NsdManager) context.getSystemService(Context.NSD_SERVICE);
    }

    public void initializeNsd() {
        initializeDiscoveryListener();
        initializeResolveListener();
    }

    public void initializeDiscoveryListener() {
        mDiscoveryListener = new NsdManager.DiscoveryListener() {

            @Override
            public void onDiscoveryStarted(String regType) {
                Log.d(TAG, "Service discovery started " + regType);
            }

            @Override
            public void onServiceFound(NsdServiceInfo service) {
                Log.d(TAG, "Service discovery success" + service);

                if(!service.getServiceType().equals(SERVICE_TYPE)){
                    Log.d(TAG, "Unknown Service Type: " + service.getServiceType());
                }
                else if(service.getServiceName().equals(mServiceName)){
                    Log.d(TAG, "Same Machine: " + mServiceName);
                }
                else if(service.getServiceName().contains(mServiceName)){
                    mNsdManager.resolveService(service, mResolveListener);
                }
            }

            @Override
            public void onServiceLost(NsdServiceInfo service) {
                Log.e(TAG, "service lost" + service);
                if (mService == service) {
                    mService = null;
                }
            }

            @Override
            public void onDiscoveryStopped(String serviceType) {
                Log.i(TAG, "Discovery stopped: " + serviceType);
            }

            @Override
            public void onStartDiscoveryFailed(String serviceType, int errorCode) {
                Log.e(TAG, "Discovery failed: Error code:" + errorCode);
                mNsdManager.stopServiceDiscovery(this);
            }

            @Override
            public void onStopDiscoveryFailed(String serviceType, int errorCode) {
                Log.e(TAG, "Discovery failed: Error code:" + errorCode);
                mNsdManager.stopServiceDiscovery(this);
            }
        };
    }

    public void initializeResolveListener() {
        mResolveListener = new NsdManager.ResolveListener() {

            @Override
            public void onResolveFailed(NsdServiceInfo serviceInfo, int errorCode) {
                Log.e(TAG, "Resolve failed" + errorCode);
            }

            @Override
            public void onServiceResolved(NsdServiceInfo serviceInfo) {
                Log.e(TAG, "Resolve Succeeded. " + serviceInfo);

                if (serviceInfo.getServiceName().equals(mServiceName)) {
                    Log.d(TAG, "Same IP.");
                    return;
                }
                mService = serviceInfo;
            }
        };
    }

    public void stopDiscovery() {
        mNsdManager.stopServiceDiscovery(mDiscoveryListener);
    }

    public NsdServiceInfo getChosenServiceInfo() {
        return mService;
    }

    public void discoverServices() {
        mNsdManager.discoverServices(
                SERVICE_TYPE, NsdManager.PROTOCOL_DNS_SD, mDiscoveryListener);
    }
}

XML 

<Button
   android:id="@+id/btn_discover_networks"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:onClick="onClickDiscover"
    android:text="Discover Networks"/>

3 个答案:

答案 0 :(得分：1)

如果应该从函数外部访问mNsdUtils，为什么不让mNsdUtils成为成员字段？

MainActivity.onClickDiscover()实现中Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.android.implicitintents.Utils.NsdUtils.discoverServices()' on a null object reference at com.example.android.implicitintents.MainActivity.onClickDiscoverAura(MainActivity.java:40) at java.lang.reflect.Method.invoke(Native Method) at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) at android.view.View.performClick(View.java:5637) at android.view.View$PerformClick.run(View.java:22429) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 的根本原因是空的。

在方法本身中实现，因为上下文不同，抛出空指针异常。

给您的一个小提示：阅读堆栈跟踪并找到您的源代码（对于您的情况，MainActivity.java），找出从下到上的第一个错误。

at com.example.android.implicitintents.MainActivity.onClickDiscoverAura(MainActivity.java:40)

这是你需要的。

.main_div{ height:260px; width:300px; -moz-box-shadow: 0px 3px 8px rgb(67, 176, 238); -webkit-box-shadow: 0px 3px 8px rgb(67, 176, 238); box-shadow: 0px 3px 6px rgba(32, 79, 182); }

答案 1 :(得分：1)

onClick没有任何问题。请阅读以下日志：

  

引起：java.lang.NullPointerException：尝试调用虚方法＆void; com com.example。在空对象引用上

这意味着在onClick＆＃34; mNsdUtils＆＃34;一片空白。如需更多帮助，请发布您的NsdUtils课程。

执行以下操作，您的应用程序不会崩溃：

DELIMITER $$
CREATE TRIGGER `insightbasev2`.`bid_AFTER_INSERT` AFTER INSERT ON `bid` 
FOR EACH ROW
BEGIN
call sp_internal_bid_history_updation_on_bid_insert("bid","created_date",null,new.created_date,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","created_id",null,new.created_id,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","name",null,new.name,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","first_delivery",null,new.first_delivery,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","email",null,new.email,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","final_delivery",null,new.final_delivery,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","master_bid_id",null,new.final_delivery,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","partner_id",null,new.partner_id,new.id);
        call sp_internal_bid_history_updation_on_bid_insert("bid","orders_id",null,new.orders_id,new.id);
END;

答案 2 :(得分：0)

onClickListener工作得很好。您必须全局实例化NSD对象，然后使用它。

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