Question

在此代码中，第一个红色交通信号灯显示，但单击按钮时不会更改。是的，我知道有类似这样的问题，但它们似乎没有帮助。所以，如果你能告诉我什么是错的，我会非常感激。

package bluetoothscanneractivity;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
import android.Manifest;

import java.util.ArrayList;

public class BluetoothScannerActivity extends AppCompatActivity {
    //private final BroadcastReceiver FoundReceiver = null;
    protected ArrayList<BluetoothDevice> foundDevices = new ArrayList<BluetoothDevice>();
    private ListView foundDevicesListView;
    private ArrayAdapter<BluetoothDevice> btArrayAdapter;

    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bluetooth_scanner);
        final BluetoothAdapter myBlueToothAdapter = BluetoothAdapter.getDefaultAdapter();

        final Button scanb = (Button) findViewById(R.id.button);
        final ListView foundDevicesListView = (ListView) findViewById(R.id.listView1);

        btArrayAdapter = new ArrayAdapter<BluetoothDevice>(this,
                android.R.layout.simple_list_item_1, foundDevices);

        foundDevicesListView.setAdapter(btArrayAdapter);

        //Turn on Bluetooth
        if (myBlueToothAdapter == null)
            Toast.makeText(BluetoothScannerActivity.this, "Your device doesnt support Bluetooth", Toast.LENGTH_LONG).show();
        else if (!myBlueToothAdapter.isEnabled()) {
            Intent BtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(BtIntent, 0);
            Toast.makeText(BluetoothScannerActivity.this, "Turning on Bluetooth", Toast.LENGTH_LONG).show();
        }

        // Quick permission check
        int permissionCheck = this.checkSelfPermission("Manifest.permission.ACCESS_FINE_LOCATION");
        permissionCheck += this.checkSelfPermission("Manifest.permission.ACCESS_COARSE_LOCATION");
        if (permissionCheck != 0) {

            this.requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION}, 1001); //Any number
        }


        scanb.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                btArrayAdapter.clear();

                myBlueToothAdapter.startDiscovery();

                Toast.makeText(BluetoothScannerActivity.this, "Scanning Devices", Toast.LENGTH_LONG).show();

            }
        });

        registerReceiver(FoundReceiver, new IntentFilter(BluetoothDevice.ACTION_FOUND));
        IntentFilter filter = new IntentFilter(
                BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
        this.registerReceiver(FoundReceiver, filter);

    }

    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        super.onDestroy();
        unregisterReceiver(FoundReceiver);
    }


    private final BroadcastReceiver FoundReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {

            String action = intent.getAction();

            // When discovery finds a new device
            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                // Get the BluetoothDevice object from the Intent
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                if (!foundDevices.contains(device)) {
                    foundDevices.add(device);
                    Toast.makeText(BluetoothScannerActivity.this, "name: " + device.getName() + " " + device.getAddress(), Toast.LENGTH_LONG).show();
                    btArrayAdapter.notifyDataSetChanged();
                }

            }

            // When discovery cycle finished
            if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                if (foundDevices == null || foundDevices.isEmpty()) {
                    Toast.makeText(BluetoothScannerActivity.this, "No Devices", Toast.LENGTH_LONG).show();
                }
            }

        }
    };


}

Answer 1

我在答案中添加了评论以显示更改。

您尚未关闭changeLights()功能。
index+!似乎是拼写错误，请使用index++添加1。
对if语句进行更改，因为它缺少最后一张图像。

var list = [
    "http://imgur.com/FHT9OoG.jpg",
    "http://imgur.com/XZ1PxGh.jpg",
    "http://imgur.com/5DUX0Wy.jpg",
    "http://imgur.com/WpeEMZU.jpg"
];
var index = 0;
function changeLights() {
index++ // Add 1 to index.
// If index is more than the array length, reset to 0
// Or you can use: if(index == list.length){
if (index > list.length-1){
index = 0;
}
var image = document.getElementById("light");
image.src=list[index];
}

<img id = "light" src="http://imgur.com/FHT9OoG.jpg">
<button type="button" onclick="changeLights()">Change Lights</button>

如果您有任何疑问，请在下面留言，我会尽快给您回复。

我希望这会有所帮助。快乐的编码！

Answer 2

您的意思是在changeLights()内将索引增加1吗？您似乎正在为索引添加!，而将其转换为字符串。

此外，您还没有关闭changeLights()功能（您只关闭了if条件。）

检查控制台，查看单击按钮时是否出现错误消息。

Answer 3

firefox中的调试器会出现以下错误：

SyntaxError: expected expression, got keyword 'if' lights.html:27:4有点神秘，所以我们看一下之前的内容，看看我们输入了!而不是1，所以我们修复它，然后再试一次。

SyntaxError: missing } after function body lights.html:32:25所以我们修复它，然后再试一次。

如何在我的红绿灯序列中改变颜色

3 个答案: