Android改变xml [重复](Android Changing xml [duplicate])

这个问题在这里已有答案：

什么是NullPointerException，我该如何解决？ 12个答案

您好我想在textView中更改文本，但不知道如何。我试着像这样改变它

TextView textView3 = (TextView) findViewById(R.id.textView3); textView3.append("hi");

但是这个textView在另一个xml文件中。

编译器输出

FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nividimka.shopapplication/com.example.nividimka.shopapplication.ShopActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403) at android.app.ActivityThread.access$600(ActivityThread.java:165) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5391) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.example.nividimka.shopapplication.ShopActivity.onCreate(ShopActivity.java:62) at android.app.Activity.performCreate(Activity.java:5122) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1150) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2315) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403) at android.app.ActivityThread.access$600(ActivityThread.java:165) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5391) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) at dalvik.system.NativeStart.main(Native Method)

This question already has an answer here:

What is a NullPointerException, and how do I fix it? 12 answers

Hello I want to change text in my textView , but dont know how. I tryed to change it like this

TextView textView3 = (TextView) findViewById(R.id.textView3); textView3.append("hi");

But this textView is in another xml-file.

the compiler outputs

FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nividimka.shopapplication/com.example.nividimka.shopapplication.ShopActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403) at android.app.ActivityThread.access$600(ActivityThread.java:165) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5391) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.example.nividimka.shopapplication.ShopActivity.onCreate(ShopActivity.java:62) at android.app.Activity.performCreate(Activity.java:5122) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1150) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2315) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403) at android.app.ActivityThread.access$600(ActivityThread.java:165) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5391) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) at dalvik.system.NativeStart.main(Native Method)

最满意答案

问题不明确，但我相信你正在尝试更新另一个活动/之前的TextView文本。然后，您可以在实际布局文件（包含textview）膨胀的类中将TextView声明为公共静态 。

Class PreviousActivity extends Activity{ public static TextView textView3 ; // inside onCreate(), after setContentView() //initialize to avoid null-pointer. textView3 = (TextView) findViewById(R.id.textView3); }

然后你可以尝试从otherActivity。

PreviousActivity.textView3 .append("new txt");

the question is not clear, but i believe you are trying to update the text of a TextView which is on another activity/previous. Then you may declare the TextView as public static in the class where the actual layout file(containing textview) inflated.

Class PreviousActivity extends Activity{ public static TextView textView3 ; // inside onCreate(), after setContentView() //initialize to avoid null-pointer. textView3 = (TextView) findViewById(R.id.textView3); }

then you can try from otherActivity.

PreviousActivity.textView3 .append("new txt");

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