蓝牙应用程序在按下按钮时崩溃

Question

I'm new to Android & was trying out the Bluetooth APIs of Google. Whenever I run my app on my phone, it crashes for some reason. I'm following the Google Developer's tutorial for the APIs & have made changes to my MainActivity.java & content.xml accordingly, but no use. Please have a look.

Here's my MainActivity.java

import android.content.Intent;
import android.content.Context;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.bluetooth.*;
import android.widget.Button;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {

    private Button btn;

    private BluetoothAdapter BA = BluetoothAdapter.getDefaultAdapter();
    private int REQUEST_ENABLE_BT = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

       /* FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });*/
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void bluetoothDiscovery()
    {
     if(BA == null)
     {
         System.out.println("System Doesn't Support Bluetooth");
     }

     if(!BA.isEnabled())
     {
         Intent enableBTIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
         startActivityForResult(enableBTIntent,REQUEST_ENABLE_BT);
         Toast.makeText(MainActivity.this,"Turned On!!", Toast.LENGTH_LONG).show();
     }
     else
     {
         Toast.makeText(MainActivity.this, "ALREADY ON", Toast.LENGTH_LONG).show();
     }


    }

}

Here's my AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="vertex2016.mvjce.edu.bluetoothapptry">
    <uses-permission android:name="android.permission.BLUETOOTH"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Here's my activity_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="vertex2016.mvjce.edu.bluetoothapptry.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        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>

    <include layout="@layout/content_main" />

  <!--  <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:onClick="bluetoothDiscovery"/> -->

</android.support.design.widget.CoordinatorLayout>

Here's my content.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="vertex2016.mvjce.edu.bluetoothapptry.MainActivity"
    tools:showIn="@layout/activity_main">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BTButton"
        android:id="@+id/button"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:onClick="bluetoothDiscovery"/>
</RelativeLayout>

And here's my logcat

03-13 02:06:34.719 18759-18759/vertex2016.mvjce.edu.bluetoothapptry E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                      Process: vertex2016.mvjce.edu.bluetoothapptry, PID: 18759
                                                                                      java.lang.IllegalStateException: Could not find method bluetoothDiscovery(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.support.v7.widget.AppCompatButton with id 'button'
                                                                                          at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:307)
                                                                                          at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:266)
                                                                                          at android.view.View.performClick(View.java:4789)
                                                                                          at android.view.View$PerformClick.run(View.java:19881)
                                                                                          at android.os.Handler.handleCallback(Handler.java:739)
                                                                                          at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                          at android.os.Looper.loop(Looper.java:135)
                                                                                          at android.app.ActivityThread.main(ActivityThread.java:5292)
                                                                                          at java.lang.reflect.Method.invoke(Native Method)
                                                                                          at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
                                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)

Thank you for your time

Answer 1

Your method bluetoothDiscovery must accept a parameter of type View , see View.onClick for reference.

public void bluetoothDiscovery(View v) {}

When this method is called, v will be the View object that was clicked.

ie

switch ( v.getId() ) {
    case R.id.button:
        // do something
        break;
    case R.id.other_button
        // do something else
        break;
}

Where r.id.button comes from your definition in XML,

android:id="@+id/button"

It is using this, you could have a single onClick method that is called by multiple buttons, each one with their own action.

Answer 2

You need a View parameter in your onClick method

public void bluetoothDiscovery(View v)

Personally, I try not to add onClick in the XML because they are hard to find as you add more classes and layouts. You can just set the OnClickListener from the Java code for clearer visibility.