java - 为什么在扩展类时会出现 ClassCastException？

Question

我正在开发一个可以从蓝牙 RFID 读取器读取数据的应用程序，但每次我启动 BluetoothActivity(这是一个选项卡式 Activity )时，它总是显示一个 ClassCastException，下面是我的代码..

BluetoothActivity 类:

package com.siscaproject.sisca.Activity;

import android.net.Uri;
import android.support.annotation.Nullable;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TabLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import android.widget.TextView;

import com.siscaproject.sisca.Fragment.RegisterFragment;
import com.siscaproject.sisca.Fragment.SearchFragment;
import com.siscaproject.sisca.R;
import com.siscaproject.sisca.Utilities.FamsModel;
import com.siscaproject.sisca.Utilities.TSLBluetoothDeviceActivity;
import com.siscaproject.sisca.Utilities.TSLBluetoothDeviceApplication;
import com.uk.tsl.rfid.asciiprotocol.AsciiCommander;
import com.uk.tsl.rfid.asciiprotocol.responders.LoggerResponder;

import java.util.ArrayList;

import butterknife.BindView;
import butterknife.ButterKnife;

public class BluetoothActivity extends TSLBluetoothDeviceActivity {
    private SectionsPagerAdapter mSectionsPagerAdapter;

    @BindView(R.id.viewpager_bluetooth) ViewPager mViewPager;
    @BindView(R.id.toolbar_bluetooth) Toolbar mToolbar;
    @BindView(R.id.tab_bluetooth) TabLayout mTabLayout;

    private FamsModel mModel;


    public AsciiCommander getCommander(){
        return ((TSLBluetoothDeviceApplication) getApplication()).getCommander();
    }


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

        ButterKnife.bind(this);

        setSupportActionBar(mToolbar);
        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        setupViewPager(mViewPager);

        mTabLayout.setupWithViewPager(mViewPager);

        AsciiCommander commander = getCommander();

        // Add the LoggerResponder - this simply echoes all lines received from the reader to the log
        // and passes the line onto the next responder
        // This is added first so that no other responder can consume received lines before they are logged.
        commander.addResponder(new LoggerResponder());

        // Add a synchronous responder to handle synchronous commands
        commander.addSynchronousResponder();


    }

    private void setupViewPager(ViewPager viewPager){
        SectionsPagerAdapter adapter = new SectionsPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new RegisterFragment(), "REGISTER");
        adapter.addFragment(new SearchFragment(), "SEARCH");
        viewPager.setAdapter(adapter);
    }


    @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_bluetooth, 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.menu_item_reconnect_reader) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public static class PlaceholderFragment extends Fragment {

        private static final String ARG_SECTION_NUMBER = "section_number";

        public PlaceholderFragment() {
        }

        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_bluetooth, container, false);
            TextView textView = (TextView) rootView.findViewById(R.id.section_label);
            textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
            return rootView;
        }
    }

    public class SectionsPagerAdapter extends FragmentPagerAdapter {

        private ArrayList<Fragment> fragmentList = new ArrayList<>();
        private ArrayList<String> fragmentTitleList = new ArrayList<>();

        public SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            return fragmentList.get(position);
        }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return fragmentList.size();
        }

        public void addFragment(Fragment fragment, String title ){
            fragmentList.add(fragment);
            fragmentTitleList.add(title);
        }

        @Nullable
        @Override
        public CharSequence getPageTitle(int position) {
            return fragmentTitleList.get(position);
        }
    }
}

TSLBluetoothDeviceActivity 类:

package com.siscaproject.sisca.Utilities;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.Toast;

import com.siscaproject.sisca.BuildConfig;
import com.uk.tsl.rfid.DeviceListActivity;
import com.uk.tsl.rfid.asciiprotocol.AsciiCommander;

import java.util.Timer;
import java.util.TimerTask;

public class TSLBluetoothDeviceActivity extends AppCompatActivity {
    // Debugging
    private static final String TAG = "TSLBTDeviceActivity";
    private static final boolean D = BuildConfig.DEBUG;

    // Intent request codes
    private static final int REQUEST_CONNECT_DEVICE_SECURE = 1;
    private static final int REQUEST_CONNECT_DEVICE_INSECURE = 2;
    private static final int REQUEST_ENABLE_BT = 3;

    // Local Bluetooth adapter
    private BluetoothAdapter mBluetoothAdapter = null;
    private BluetoothDevice mDevice = null;

    protected AsciiCommander getCommander() {
        return ((TSLBluetoothDeviceApplication) getApplication()).getCommander();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Get local Bluetooth adapter
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

        // Create the AsciiCommander to talk to the reader (if it doesn't already exist)
        if (getCommander() == null) {
            try {
                TSLBluetoothDeviceApplication app = (TSLBluetoothDeviceApplication) getApplication();
                AsciiCommander commander = new AsciiCommander(getApplicationContext());
                app.setCommander(commander);

            } catch (Exception e) {
                fatalError("Unable to create AsciiCommander!");
            }
        }
    }


    // Terminate the app with the given message
    private void fatalError(String message) {
        Toast.makeText(this, message, Toast.LENGTH_LONG).show();
        Timer t = new Timer();
        t.schedule(new TimerTask() {
            public void run() {
                finish();
            }
        }, 1800);
    }

    protected void bluetoothNotAvailableError(String message) {
        fatalError(message);
    }


    @Override
    public void onStart() {
        super.onStart();

        // If no other attempt to connect is ongoing try to connect to last used reader
        // Note: When returning from the Device List activity
        if (mBluetoothAdapter.isEnabled()) {
            if (mDevice == null) {
                // Attempt to reconnect to the last reader used
                Toast.makeText(this, "Reconnecting to last used reader...", Toast.LENGTH_SHORT).show();

                getCommander().connect(null);
            }
        } else {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }
    }

    @Override
    public void onStop() {
        super.onStop();

        getCommander().disconnect();
        mDevice = null;
    }

    protected void connectToDevice(Intent deviceData, boolean secure) {
        Toast.makeText(this.getApplicationContext(), "Connecting...", Toast.LENGTH_LONG).show();
        // Get the device MAC address
        String address = deviceData.getExtras()
                .getString(DeviceListActivity.EXTRA_DEVICE_ADDRESS);
        // Get the BluetoothDevice object
        mDevice = mBluetoothAdapter.getRemoteDevice(address);
        // Attempt to connect to the device
        if (mDevice != null) {
            getCommander().connect(mDevice);
        } else {
            if (D) Log.e(TAG, "Unable to obtain BluetoothDevice!");
        }
    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {

        if (D)
            Log.d(TAG, "selectDevice() onActivityResult: " + resultCode + " for request: " + requestCode);

        switch (requestCode) {
            case REQUEST_CONNECT_DEVICE_SECURE:
                // When DeviceListActivity returns with a device to connect
                if (resultCode == Activity.RESULT_OK) {
                    connectToDevice(data, true);
                }
                break;
            case REQUEST_CONNECT_DEVICE_INSECURE:
                // When DeviceListActivity returns with a device to connect
                if (resultCode == Activity.RESULT_OK) {
                    connectToDevice(data, false);
                }
                break;
            case REQUEST_ENABLE_BT:
                // When the request to enable Bluetooth returns
                if (resultCode != Activity.RESULT_OK) {
                    // User did not enable Bluetooth or an error occurred
                    Log.d(TAG, "BT not enabled");
                    bluetoothNotAvailableError("Bluetooth was not enabled\nApplication Quitting...");
                }
        }
    }


    public void selectDevice() {
        // Launch the DeviceListActivity to see devices and do scan
        Intent serverIntent = new Intent(this, DeviceListActivity.class);
        startActivityForResult(serverIntent, REQUEST_CONNECT_DEVICE_INSECURE);
    }

    public void disconnectDevice() {
        mDevice = null;
        getCommander().disconnect();
    }

    public void reconnectDevice() {
        getCommander().connect(null);
    }
}

错误日志:

11-21 14:47:54.836 18956-18956/com.siscaproject.sisca E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.siscaproject.sisca, PID: 18956
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.siscaproject.sisca/com.siscaproject.sisca.Activity.BluetoothActivity}: java.lang.ClassCastException: android.app.Application cannot be cast to com.siscaproject.sisca.Utilities.TSLBluetoothDeviceApplication
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2318)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396)
        at android.app.ActivityThread.access$800(ActivityThread.java:139)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:149)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.ClassCastException: android.app.Application cannot be cast to com.siscaproject.sisca.Utilities.TSLBluetoothDeviceApplication
        at com.siscaproject.sisca.Activity.BluetoothActivity.getCommander(BluetoothActivity.java:51)
        at com.siscaproject.sisca.Utilities.TSLBluetoothDeviceActivity.onCreate(TSLBluetoothDeviceActivity.java:45)
        at com.siscaproject.sisca.Activity.BluetoothActivity.onCreate(BluetoothActivity.java:57)
        at android.app.Activity.performCreate(Activity.java:5411)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2396) 
        at android.app.ActivityThread.access$800(ActivityThread.java:139) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1293) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:149) 
        at android.app.ActivityThread.main(ActivityThread.java:5257) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:515) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609) 
        at dalvik.system.NativeStart.main(Native Method) 

我从一个运行良好的应用程序中遵循了这段代码，但是当我在我的项目中实现它时，它总是显示这个错误，我不确定我做错了什么。

---编辑---

TSLBluetoothDeviceApplication 类:

package com.siscaproject.sisca.Utilities;

import android.app.Application;

import com.uk.tsl.rfid.asciiprotocol.AsciiCommander;


public class TSLBluetoothDeviceApplication extends Application {
    private static AsciiCommander commander = null;

    /// Returns the current AsciiCommander
    public AsciiCommander getCommander() {
        return commander;
    }

    /// Sets the current AsciiCommander
    public void setCommander(AsciiCommander _commander) {
        commander = _commander;
    }

}

Android list :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.siscaproject.sisca">

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH_PRIVILEGED" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.VIBRATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        tools:replace="android:icon">
        <activity
            android:name=".Activity.LoginActivity"
            android:screenOrientation="portrait">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Activity.BluetoothTestActivity"
            android:theme="@style/StandardTheme" />
        <activity
            android:name=".Activity.HomeActivity"
            android:label="@string/title_activity_home"
            android:theme="@style/AppTheme" />

        <meta-data
            android:name="com.google.android.gms.vision.DEPENDENCIES"
            android:value="barcode" />

        <activity android:name=".Activity.QRActivity" />
        <activity
            android:name=".Activity.BluetoothActivity"
            android:label="@string/title_activity_bluetooth"
            android:theme="@style/AppTheme"></activity>
    </application>

</manifest>

Answer 1

getApplication() Activity 内部返回类型为 Application 的对象.在您的情况下，您试图将此对象转换为 TSLBluetoothDeviceApplication根据您的定义，它是一个 Activity类型类。

如我所见，您正在尝试调用 getCommander()已在您的 TSL Activity 类中定义。我假设你想要 getCommander()来自另一个类的方法。请确定是哪一个。

public AsciiCommander getCommander(){
    return ((TSLBluetoothDeviceApplication) getApplication()).getCommander();
}

这个方法已经在TSLBluetoothDeviceApplication里面了类.. 我不知道你试图通过调用你当前类中已经存在的相同方法来实现什么。

编辑:

编辑后的帖子，我们注意到该类已正确实现，只是忘了添加 android:name="com.path.to.ApplicationClass"进入Manifest <application/> 下的文件标签。

我也会让上面的答案，因为它可能会帮助别人快乐编码<3