java.lang.NullPointerException：尝试在空对象引用上调用虚方法’boolean java.lang.String.equals（java.lang.Object）’

我在运行我的项目时遇到错误。

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.olympic/com.prima.olympic.ProductDetail}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference 

这是完整的日志：

 06-06 23:12:45.561: E/AndroidRuntime(17135): FATAL EXCEPTION: main 06-06 23:12:45.561: E/AndroidRuntime(17135): Process: com.example.olympic, PID: 17135 06-06 23:12:45.561: E/AndroidRuntime(17135): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.olympic/com.prima.olympic.ProductDetail}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2693) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.ActivityThread.access$900(ActivityThread.java:177) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.os.Handler.dispatchMessage(Handler.java:102) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.os.Looper.loop(Looper.java:145) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.ActivityThread.main(ActivityThread.java:5942) 06-06 23:12:45.561: E/AndroidRuntime(17135): at java.lang.reflect.Method.invoke(Native Method) 06-06 23:12:45.561: E/AndroidRuntime(17135): at java.lang.reflect.Method.invoke(Method.java:372) 06-06 23:12:45.561: E/AndroidRuntime(17135): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1389) 06-06 23:12:45.561: E/AndroidRuntime(17135): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1184) 06-06 23:12:45.561: E/AndroidRuntime(17135): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference 06-06 23:12:45.561: E/AndroidRuntime(17135): at com.prima.olympic.ProductDetail.onCreate(ProductDetail.java:85) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.Activity.performCreate(Activity.java:6289) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119) 06-06 23:12:45.561: E/AndroidRuntime(17135): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646) 

这是我的ProductDetail.java

 public class ProductDetail extends Activity { Button btnAddtoShoppingList; Button btnDeleteShoppingList; TextView detail_productType; TextView detail_wdh; TextView detail_volume; TextView detail_weight; TextView detail_cont20; TextView detail_cont40; TextView detail_pack; TextView detail_quantity; TextView detail_colour; TextView detail_cetegories; TextView detail_series; TextView detail_price; ImageView detail_imageView; String shown_id, shown_type, shown_wdh, shown_volume, shown_weight, shown_cont20, shown_cont40, shown_pack, shown_quantity, shown_colour, shown_categories, shown_series, shown_price; String customer_id, error_message ; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_product_detail); btnAddtoShoppingList = (Button)findViewById(R.id.btnAddtoShoppingList); btnDeleteShoppingList = (Button)findViewById(R.id.btnDeleteShoppingList); SharedPreferences userInformation = getApplicationContext().getSharedPreferences("userinfo", 0); customer_id = userInformation.getString("customer_id", "none"); detail_productType = (TextView)findViewById(R.id.detail_productType); detail_wdh = (TextView)findViewById(R.id.detail_wdh); detail_volume = (TextView)findViewById(R.id.detail_volume); detail_weight = (TextView)findViewById(R.id.detail_weight); detail_cont20 = (TextView)findViewById(R.id.detail_cont20); detail_cont40 = (TextView)findViewById(R.id.detail_cont40); detail_pack = (TextView)findViewById(R.id.detail_pack); detail_quantity = (TextView)findViewById(R.id.detail_quantity); detail_colour = (TextView)findViewById(R.id.detail_colour); detail_cetegories = (TextView)findViewById(R.id.detail_categories); detail_series = (TextView)findViewById(R.id.detail_series); detail_price = (TextView)findViewById(R.id.detail_price); detail_imageView = (ImageView)findViewById(R.id.detail_imageView); // Get Value from previous activity Intent i = getIntent(); shown_id = i.getStringExtra("shown_id"); shown_type = i.getStringExtra("shown_type"); shown_wdh = i.getStringExtra("shown_wdh"); shown_volume = i.getStringExtra("shown_volume"); shown_weight = i.getStringExtra("shown_weight"); shown_cont20 = i.getStringExtra("shown_cont20"); shown_cont40 = i.getStringExtra("shown_cont40"); shown_pack = i.getStringExtra("shown_pack"); shown_quantity = i.getStringExtra("shown_quantity"); shown_colour = i.getStringExtra("shown_colour"); shown_categories = i.getStringExtra("shown_categories"); shown_series = i.getStringExtra("shown_series"); shown_price = i.getStringExtra("shown_price"); String checkOrigin = i.getStringExtra("from_activity"); if(checkOrigin.equals("shoppinglist")){ btnAddtoShoppingList.setVisibility(View.GONE); btnDeleteShoppingList.setVisibility(View.VISIBLE); } Bitmap bitmap = (Bitmap) i.getParcelableExtra("shown_bitmap"); detail_productType.setText("PRODUCT TYPE : "+shown_type); detail_wdh.setText("W x D x H : "+shown_wdh); detail_volume.setText("VOLUME : "+shown_volume); detail_weight.setText("WEIGHT : "+shown_weight); detail_cont20.setText("CONT20 : "+shown_cont20); detail_cont40.setText("CONT40 : "+shown_cont40); detail_pack.setText("PACK : "+shown_pack); detail_quantity.setText("QUANTITY : "+shown_quantity); detail_colour.setText("COLOUR : "+shown_colour); detail_cetegories.setText("CATEGORIES : "+shown_categories); detail_series.setText("SERIES : "+shown_series); detail_price.setText("PRICE : Rp "+shown_price); detail_imageView.setImageBitmap(bitmap); btnAddtoShoppingList.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { addtoShoppingListTask addtoShoppingList = new addtoShoppingListTask(); addtoShoppingList.execute((Void) null); } }); btnDeleteShoppingList.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { deleteShoppingListTask deletetoShoppingList = new deleteShoppingListTask(); deletetoShoppingList.execute((Void) null); } }); } 

任何人都可以告诉我错误在哪里以及如何解决它？ 如果有人可以帮助，我会非常感激。

Answer 1

您的String checkOrigin为null从而为您提供NullPointerException 。 这是导致它的原因：

 String checkOrigin = i.getStringExtra("from_activity"); if(checkOrigin.equals("shoppinglist")){ btnAddtoShoppingList.setVisibility(View.GONE); btnDeleteShoppingList.setVisibility(View.VISIBLE); } 

String checkOrigin为null因为您没有从Intent接收任何值。 这可能是因为您忘记传递上一个Activity的值。
但是，您可以检查String是否为null ，如果是，则不会执行这些操作。 您可以通过以下方式执行此操作：

 String checkOrigin = i.getStringExtra("from_activity"); if(checkOrigin != null && checkOrigin.equals("shoppinglist")){ btnAddtoShoppingList.setVisibility(View.GONE); btnDeleteShoppingList.setVisibility(View.VISIBLE); } 

因此，如果checkOrigin为null，则不会执行这些操作。

但我建议检查您正在接收Intent的Activity ，以确保您正确地发送和接收Intent 。

如果您想了解有关NullPointerException的更多信息，请查看此问题及其答案以获取更多详细信息 。

Answer 2

将 to 更改 to ，因为视图与空视图无关。 这是通过类attr定义的自定义视图，如下所示：

你有错误

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference 

Answer 3

checkOrigin为null

 String checkOrigin = i.getStringExtra("from_activity"); if(checkOrigin!=null && checkOrigin.equals("shoppinglist")){ btnAddtoShoppingList.setVisibility(View.GONE); btnDeleteShoppingList.setVisibility(View.VISIBLE); }