Android 应用中 setText 上的空对象引用 [英] Null object reference on setText in Android app
问题描述
我的应用程序在此 setText
此处崩溃.我想可能是因为它找不到 id,所以我查看了 R.java 并在那里找到了 id.我很困惑为什么它仍然崩溃.
My app crashes on this setText
here. I think probably because it cannot find the id so I looked into to R.java and found the id there. I'm confused why it still crashes.
TextView city = (TextView)findViewById(R.id.city_result);
city.setText(msg[0]);
R.java
public static final int city_result=0x7f080041;
并且这段代码在public static final class id
方法中.
and this code is in the public static final class id
method.
任何帮助将不胜感激!谢谢!!
Any help will be appreciated! Thanks!!
================更多代码:
================ More Code:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_weather_report);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
//get message from intent
Intent intent = getIntent();
String[] message = intent.getStringArrayExtra(MainActivity.EXTRA_MESSAGE);
setResult(message);
}
public void setResult(String[] msg)
{
//test
TextView city = (TextView)findViewById(R.id.city_result);
city.setText(msg[0]);
}
这个文件我刚开始,其他地方只是系统生成的新文件代码,我还没有编辑.这是 logcat:
This file I just started, elsewhere is just system generated new file code, I didn't edit yet. Here's logcat:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.chen.weather/com.example.chen.weather.WeatherReport}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.chen.weather.WeatherReport.setResult(WeatherReport.java:78)
at com.example.chen.weather.WeatherReport.onCreate(WeatherReport.java:32)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
推荐答案
NullPointerException: 尝试调用虚方法 'voidandroid.widget.TextView.setText
NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText
表示 city
TextView 对象为 null
由于:
Means city
TextView object is null
due to :
1. setContentView
在使用 findViewById
之前不会被调用:
1. setContentView
is not called before using findViewById
:
2. 不使用 TextView
定义为 city_result
id 的布局.确保在 setContentView
2. Not using layout in which TextView
is defined with city_result
id. make sure you are passing right layout in setContentView
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