从Java文件更新文本视图时出错

Question

抱歉，这可能是一个简单的错误，对Android开发人员来说是新的，但是我一直在网上寻找答案，而这些解决方案似乎都不起作用。每当我尝试运行下面的代码时，都会提示为什么/如何修复它的任何想法。首先是java文件

public class Services extends Activity {
Report2 r;  
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Bundle data = getIntent().getExtras();

    r = data.getParcelable("RemarksReport");

    setContentView(R.layout.activity_services);

    TextView sampleText = (TextView) findViewById(R.id.services_text);

一直工作到这里，然后在下一行崩溃

    sampleText.setText("ANYTHING");

    if (savedInstanceState == null) {
        getFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
}

XML文件中的部分看起来像这样，

        <TextView
        android:id="@+id/services_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="#000000"
        android:textSize="42px"
        android:text="@string/sample_services" />

它在表格中的位置，呈线性布局。

Logcat错误：

07-01 22:45:09.952: E/AndroidRuntime(8854): FATAL EXCEPTION: main
07-01 22:45:09.952: E/AndroidRuntime(8854): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jasc/com.example.jasc.Services}: java.lang.NullPointerException
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.ActivityThread.access$600(ActivityThread.java:127)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.os.Looper.loop(Looper.java:137)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.ActivityThread.main(ActivityThread.java:4441)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at java.lang.reflect.Method.invokeNative(Native Method)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at java.lang.reflect.Method.invoke(Method.java:511)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at dalvik.system.NativeStart.main(Native Method)
07-01 22:45:09.952: E/AndroidRuntime(8854): Caused by: java.lang.NullPointerException
07-01 22:45:09.952: E/AndroidRuntime(8854):     at com.example.jasc.Services.onCreate(Services.java:30)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.Activity.performCreate(Activity.java:4465)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
07-01 22:45:09.952: E/AndroidRuntime(8854):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)

Answer 1

在片段的内部onCreateView更改如下：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.place_holder_fragment, container, false);
    servicesTxtView= (TextView) view.findViewById(R.id.services_text);
    servicesTxtView.setText("ANYTHING");
    return view;
}

您尝试不使用其容器视图来初始化textview。因此，您在调用setText它时会得到Null Pointer Exception 。