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）&

本文介绍了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）'的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

运行时我的项目出错了。

I'm getting error when runtime my project.

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

This is my 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好吗？如果有人可以提供帮助我会非常感激。

can anyone tell me where is the error and how to fix it please? if anyone can help i will be so thankful.

推荐答案

你的字符串 checkOrigin 是 null 因此给你一个 NullPointerException 。这就是造成它的原因：

Your String checkOrigin is null thus giving you a NullPointerException. This is what is causing it:

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

字符串 checkOrigin 是 null ，因为您没有从 Intent 中收到任何值。这可能是因为您忘记从先前的活动传递值。 但是，您可以检查您的String是否 null 如果是，则不执行这些操作。您可以通过以下方式执行此操作：

The String checkOrigin is null because you are not receiving any value from your Intent. This might be because you forgot to pass a value from your previous Activity. However, you can check to see if your String is null and if it is, then those actions won't be performed. You would do this by the following:

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，则不执行这些操作。

Therefore, if checkOrigin is null, then those actions won't be performed.

但我建议您检查活动您收到的意图来确保您正确地发送和接收意图。

But I would recommend checking the Activity that you are receiving the Intent from to make sure that you are sending and receiving the Intent correctly.

如果你想要阅读更多关于 NullPointerException 的信息，请查看这个问题及其更多细节的答案。

If you want to read more about NullPointerExceptions, have a look at this question and its answers for more detail.