java - 我无法更改 TextView 中的文本

Question

我可以在 DataOutputActivity.java 中使用 System.out.println() 打印变量值(纬度、经度、imageloc)，但是当我尝试使用上述变量之一设置 textview 的文本时，应用程序关闭.我还在布局文件中声明了 TextView 的 ID。我不知道出了什么问题。没有语法错误，只有运行时错误。如果我删除 onCreate() 方法的最后两行，则没有问题。

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_data_ouput);

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
        Intent intent = getIntent();
        String latitude = intent.getStringExtra(HomeActivity.EXTRA_LATITUDE);
        String longitude = intent.getStringExtra(HomeActivity.EXTRA_LONGITUDE);
        String imageLoc = intent.getStringExtra(HomeActivity.EXTRA_IMAGELOC);
        TextView textview = (TextView) findViewById(R.id.outputText);
        textview.setText(latitude);
        setContentView(textview);
    }

fragment 数据输出.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.urbsalus.DataOuputActivity$PlaceholderFragment" >

    <TextView 
        android:id="@+id/outputText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/Latitude"
        />

</RelativeLayout>

字符串.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="title_activity_data_ouput">DataOuputActivity</string>
    <string name="Latitude">Latitude</string>

</resources>

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07-22 17:04:18.761: D/OpenGLRenderer(15827): Flushing caches (mode 0)
07-22 17:04:19.231: D/OpenGLRenderer(15827): Flushing caches (mode 2)
07-22 17:04:19.651: D/OpenGLRenderer(15827): Flushing caches (mode 0)
07-22 17:04:20.201: D/memalloc(15827): /dev/pmem: Unmapping buffer base:0x51fb1000 size:6144000 offset:4608000
07-22 17:04:20.211: D/memalloc(15827): /dev/pmem: Unmapping buffer base:0x525f3000 size:7680000 offset:6144000
07-22 17:04:20.321: D/CLIPBOARD(15827): Hide Clipboard dialog at Starting input: finished by someone else... !
07-22 17:04:20.341: W/IInputConnectionWrapper(15827): showStatusIcon on inactive InputConnection
07-22 17:04:30.181: D/AndroidRuntime(15827): Shutting down VM
07-22 17:04:30.181: W/dalvikvm(15827): threadid=1: thread exiting with uncaught exception (group=0x40c0da68)
07-22 17:04:30.191: E/AndroidRuntime(15827): FATAL EXCEPTION: main
07-22 17:04:30.191: E/AndroidRuntime(15827): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.urbsalus/com.example.urbsalus.DataOuputActivity}: java.lang.NullPointerException
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.ActivityThread.access$600(ActivityThread.java:128)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.os.Looper.loop(Looper.java:137)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.ActivityThread.main(ActivityThread.java:4517)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at java.lang.reflect.Method.invokeNative(Native Method)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at java.lang.reflect.Method.invoke(Method.java:511)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at dalvik.system.NativeStart.main(Native Method)
07-22 17:04:30.191: E/AndroidRuntime(15827): Caused by: java.lang.NullPointerException
07-22 17:04:30.191: E/AndroidRuntime(15827):    at com.example.urbsalus.DataOuputActivity.onCreate(DataOuputActivity.java:30)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.Activity.performCreate(Activity.java:4470)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
07-22 17:04:30.191: E/AndroidRuntime(15827):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
07-22 17:04:30.191: E/AndroidRuntime(15827):    ... 11 more
07-22 17:04:38.141: I/Process(15827): Sending signal. PID: 15827 SIG: 9

Answer 1

首先，删除这一行，它是不正确的。

setContentView(textview);

第二行

String latitude = intent.getStringExtra(HomeActivity.EXTRA_LATITUDE);

您正在尝试从 Intent 中的 Extras 获取字符串(您不是从 Resources 文件中读取)。如果 HomeActivity.EXTRA_LATITUDE 中的值不存在，则该字符串将返回为 null，因此出现空指针错误。

你可以通过做类似的事情来检查这一点

if (latitude != null) {
    textview.setText(latitude);
}