尝试调用虚拟方法 ‘java.lang.Object android.content.Context’

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英文:

Attempt to invoke virtual method 'java.lang.Object android.content.Context

问题

guys我创建了这个新类但是当我在MainActivity中调用这个vibrate函数时出现了错误

public class vibrate extends Activity {

    public void vibrate() {
        try {
            Vibrator v = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
            // 震动500毫秒
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                v.vibrate(VibrationEffect.createOneShot(200, VibrationEffect.DEFAULT_AMPLITUDE));
            } else {
                // 在API 26中已弃用
                v.vibrate(200);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这是我调用这个类的方式

vibrate v = new vibrate();
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    v.vibrate();
}

这是错误信息

W/System.err: java.lang.NullPointerException: 尝试调用空对象引用上的 'java.lang.Object android.content.Context.getSystemService(java.lang.String)'
英文:

guys i make this new class but when i call this function vibrate in Main Activity i have error

public class vibrate  extends Activity{

public void vibrate() {
        try {
            Vibrator v = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
            // Vibrate for 500 milliseconds
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                v.vibrate(VibrationEffect.createOneShot(200, VibrationEffect.DEFAULT_AMPLITUDE));
            } else {
                //deprecated in API 26
                v.vibrate(200);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
}

and this how i called this class

 vibrate v = new vibrate() ;
 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        v.vibrate();
       
    }

this is the error

W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference

答案1

得分: 1

Class vibrate 是 Activity 的子类,当你像这样创建一个实例时,你正在创建一个 activity。但这不是正确的创建 activity 的方式。

vibrate v = new vibrate()

你必须在 AndroidManifest.xml 文件中声明你的 activity,并通过使用 intent 来调用该 activity。

Intent intent = new Intent(this, vibrate.class);
startActivity(intent);

但是要使用 Vibrator,你只需要这样做。

public class VibrateActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        vibrate();
    }

    private void vibrate() {
        Vibrator vibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
        if (vibrator != null) {
            // 震动 500 毫秒
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                vibrator.vibrate(VibrationEffect.createOneShot(200, VibrationEffect.DEFAULT_AMPLITUDE));
            } else {
                // 在 API 26 中已弃用
                vibrator.vibrate(200);
            }
        }
    }
}

不要忘记在 AndroidManifest.xml 文件中包含权限:

<uses-permission android:name="android.permission.VIBRATE"/>

更新:
在不在 activity 中执行的情况下使用单独的类。

public class Vibrate extends Activity {

    public void vibrate(Context context) {
        Vibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
        if (vibrator != null) {
            // 震动 500 毫秒
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                vibrator.vibrate(VibrationEffect.createOneShot(200, VibrationEffect.DEFAULT_AMPLITUDE));
            } else {
                // 在 API 26 中已弃用
                vibrator.vibrate(200);
            }
        }
    }
}

然后在你的 activity 中像这样使用它。

Vibrate vibrate = new Vibrate();
vibrate.vibrate(this);
英文:

Class vibrate is a subclass of Activity, when you create an instance like this, you are creating an activity. But it's not a right way to create an activity.

vibrate v = new vibrate()

You have to declare your activity inside AndroidManifest.xml file, and invoke the activity by using intent.

Intent intent = new Intent(this, vibrate.class);
startActivity(intent);

But to use the Vibrator, you just need to do like this.

public class VibrateActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        vibrate();
    }

    private void vibrate() {
        Vibrator vibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
        if (vibrator != null) {
            // Vibrate for 500 milliseconds
            if (Build.VERSION.SDK_INT &gt;= Build.VERSION_CODES.O) {
                v.vibrate(VibrationEffect.createOneShot(200, VibrationEffect.DEFAULT_AMPLITUDE));
            } else {
                //deprecated in API 26
                v.vibrate(200);
            }
        }
}

Don't forget to include permission in AndroidManifest.xml file:

&lt;uses-permission android:name=&quot;android.permission.VIBRATE&quot;/&gt;

UPDATE:
Use separate class without doing in the activity.

public class Vibrate extends Activity {

    public void vibrate(Context context) {
        Vibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
        if (vibrator != null) {
            // Vibrate for 500 milliseconds
            if (Build.VERSION.SDK_INT &gt;= Build.VERSION_CODES.O) {
                v.vibrate(VibrationEffect.createOneShot(200, VibrationEffect.DEFAULT_AMPLITUDE));
            } else {
                //deprecated in API 26
                v.vibrate(200);
            }
        }
}

And use it like this in your activity.

Vibrate vibrate = new Vibrate();
vibrate.vibrate(this)

答案2

得分: 0

在onCreate()中初始化vibrate v = new vibrate();并调用v.vibrate();不需要将vibrate作为一个Activity。

英文:

Initialize vibrate v = new vibrate(); in onCreate()
and call v.vibrate();
No need to make vibrate as an Activity.

huangapple
  • 本文由 发表于 2020年8月23日 15:56:20
  • 转载请务必保留本文链接:https://go.coder-hub.com/63544665.html
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