Android和Java无法解析为某种类型

Question

Trying to call a method held in another class in Android. I've only just started Android development today so this is all new to me. All I'm wanting to do is have my code run with the click of a button.

However, in my button code, I've got an issue where the IDE tells it cannot be resolved to a type. Can anyone help me in fixing this?

Then my main activity class. This is where the error is:

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.Button;

public class MainActivity extends Activity {
Button aButton;

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

    addListeners();



}

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

private void addListeners() {
      Button btnCallMethod = (Button) this.findViewById(R.id.btnCallMethod);

      // CALL METHOD BUTTON
      btnCallMethod.setOnTouchListener(new OnTouchListener() {

         @Override
         public boolean onTouch(View v, MotionEvent event) {
         if (event.getAction() == MotionEvent.ACTION_UP) {
              // error is on this line below
               Intent intent = new Intent(getApplicationContext(), DeviceScanActivity.class);
               startActivity(intent); // start the DeciveScanActivity
             }
             return false;
           }
         });
        }
}

Update the code for my DeviceScanActivity class:

import android.annotation.TargetApi;
import android.app.ListActivity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothManager;
import android.content.Context;
import android.os.Bundle;
import android.os.Handler;
import android.widget.ArrayAdapter;


@TargetApi(18)
public class DeviceScanActivity extends ListActivity {

    private Handler mHandler;

    // Stops scanning after 10 seconds.
    private static final long SCAN_PERIOD = 10000;

    private ArrayAdapter<Object> list;
    protected void OnCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);


        Bundle b = getIntent().getExtras();
        int key = b.getInt("yourKey");

        switch(key)
        {
           case 1: // call method here

            list = new ArrayAdapter<Object>(getApplicationContext(), 
                    android.R.layout.simple_list_item_1);
            setListAdapter(list);
            scanLeDevice(true);
        }

    }

    @TargetApi(18)
    public void scanLeDevice(final boolean enable) {
        list.add("Scanning...");
        final BluetoothAdapter adapter = getBluetoothAdapter();
        if (enable) {
            // Stops scanning after a pre-defined scan period.
            mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    // mBluetoothAdapter.stopLeScan(mLeScanCallback);
                    adapter.stopLeScan(callback);
                    list.clear();
                }
            }, SCAN_PERIOD);

            adapter.startLeScan(callback);
        } else {
            adapter.stopLeScan(callback);
        }

    }
    @TargetApi(18)
    private BluetoothAdapter getBluetoothAdapter()
    {
        BluetoothManager manager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
        return manager.getAdapter();
    }
    private final BluetoothAdapter.LeScanCallback callback = new BluetoothAdapter.LeScanCallback() 
    {

        @Override
        public void onLeScan(final BluetoothDevice device, int rssi, byte[] scanRecord) {
            // TODO Auto-generated method stub

            {
                list.add("found: " + device);
                runOnUiThread(new Runnable(){
                    @Override
                    public void run()
                    {
                        list.add(device);
                        list.notifyDataSetChanged();
                    }
                });
        }
    }
    };

}

Also my manifest Xml which I think is important for Android:

<?xml version="1.0" encoding="utf-8"?>

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

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

Answer 1

You need to make sure that when you add a new class( DeviceScanActivity in this case), you add it to the correct package.

When you right-click on your project and click "New -> Class", it doesn't populate the package name for you. There are two ways to make sure it gets added to the proper package:

• Instead of right-clicking the project to add a class, right-click the package .

  • Your projects packages can be found in either the Package Explorer or Project explorer by expanding the src folder. the next layer down should be packages.

• You can add the package name manually to the New Java Class dialog. "Package" should be near the top.

Note, this assumes you are using Eclipse IDE / ADT. If not, the exact steps might be different.

---

Secondly, you need to add any new Activity classes to your manifest. You won't get a Can't be resolved to a type error if it's not, but you'll get a runtime error, so go ahead and fix it while you're there. At a very minimum, you need something like:

<activity
    android:name="com.example.bletest.DeviceScanActivity"
</activity>

Answer 2

Try this:

btnCallMethod.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {

                Intent intent = new Intent(getApplicationContext(), DeviceScanActivity.class);
               startActivity(intent);
            }
        });

Answer 3

I got the same error.I just cleaned the project after doing all the possible things.Then errors went. But make sure to have a backup of the project before you clean it because sometimes the R file may disappear.