android - Android 中的 ToggleButton NullPointerException

Question

我正在尝试使用切换按钮来切换设备中的蓝牙服务。但是当我第二次单击切换按钮时，活动总是崩溃。任何建议将不胜感激！谢谢！

activity_main.xml

        <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <LinearLayout 
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="center_horizontal">

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="left"
            android:text="Settings"
            tools:ignore="HardcodedText" />

        <ToggleButton
            android:id="@+id/toggleButton1"
            android:layout_width="0dip"
            android:layout_height="wrap_content"
            android:layout_gravity="fill"
            android:layout_weight="1.0"
            android:textOn="Turn Off"
            android:textOff="Turn On"
            android:onClick="onToggleClicked"
            tools:ignore="HardcodedText" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="right"
            android:text="Devices"
            tools:ignore="HardcodedText" />

    </LinearLayout>

    <GridView
        android:id="@+id/gridView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        android:numColumns="3" >
    </GridView>        

</LinearLayout>

MainActivity.java

public class MainActivity extends Activity {        
private static final int REQUEST_ENABLE_BT = 0; 
final BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

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

    if (mBluetoothAdapter == null) {
       Toast.makeText(getApplicationContext(), "Device not supported!", Toast.LENGTH_LONG).show();
    }               
}

public void onToggleClicked(View v)
{                      
    final ToggleButton toggle;
    Boolean toggleStatus;
    toggle = (ToggleButton)findViewById(R.id.toggleButton1);

    toggleStatus = ((ToggleButton)v).isChecked();

    if(toggleStatus)
    {
        toggle.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                if (!mBluetoothAdapter.isEnabled()) {
                    Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                    startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
                    Toast.makeText(getApplicationContext(), "Enabling Bluetooth..", Toast.LENGTH_LONG).show();
                }                               
            }
        });
    }
    else
    {
        toggle.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                if (mBluetoothAdapter.isEnabled()) {
                    mBluetoothAdapter.disable();
                    Toast.makeText(getApplicationContext(), "Disabling Bluetooth..", Toast.LENGTH_LONG).show();
                }                               
            }
        });
    }

}

Answer 1

我猜这是因为您试图从 OnClickListener 本身更改 ToggleButton 的 OnClickListener。

您已经在 XML 中设置了 OnClickListener android:onClick="onToggleClicked"，因此无需在代码中再次执行此操作onToggleClicked

然后，您的点击处理程序应变为：

public void onToggleClicked(View v)
{                      
    final ToggleButton toggle;
    Boolean toggleStatus;
    toggle = (ToggleButton)findViewById(R.id.toggleButton1);

    toggleStatus = ((ToggleButton)v).isChecked();

    if(toggleStatus)
    {
                if (!mBluetoothAdapter.isEnabled()) {
                    Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                    startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
                    Toast.makeText(getApplicationContext(), "Enabling Bluetooth..", Toast.LENGTH_LONG).show();
                }                               
    }
    else
    {
                if (mBluetoothAdapter.isEnabled()) {
                    mBluetoothAdapter.disable();
                    Toast.makeText(getApplicationContext(), "Disabling Bluetooth..", Toast.LENGTH_LONG).show();
                }                               
    }
}