Java OnClickListener在startActivity上抛出NullPointerException
我正在使用Android API 17和Android开发工具(ADT),我有一个帮助Button,它正在监听点击事件HelpButtonListener正在侦听Help按钮的单击事件,如下所示: 摘自MainActivity.javaJava OnClickListener在startActivity上抛出NullPointerException,java,android,android-intent,android-activity,roboguice,Java,Android,Android Intent,Android Activity,Roboguice,我正在使用Android API 17和Android开发工具(ADT),我有一个帮助Button,它正在监听点击事件HelpButtonListener正在侦听Help按钮的单击事件,如下所示: 摘自MainActivity.java private final class HelpButtonListener implements OnClickListener { public void onClick(View v) { Intent mai
private final class HelpButtonListener implements OnClickListener {
public void onClick(View v) {
Intent mainToHelpIntent = new Intent(MainActivity.this, HelpActivity.class);
startActivity(mainToHelpIntent);
}
}
public class HelpActivity extends RoboActivity {
@InjectView(R.id.helpTextView)
private TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
helpTextView.setText("Some helpful stuff..");
setContentView(R.layout.activity_help);
}
}
以下帮助活动的代码非常有效,ans向我展示了一些有用的东西。关于帮助活动的创建:
public class HelpActivity extends RoboActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
TextView helpTextView = new TextView(HelpActivity.this);
helpTextView.setText("Some helpful stuff..");
setContentView(helpTextView);
}
}
但是,如果我尝试使用RoboGuice 2注入的TextView
view组件中的文本设置来使用以下代码注入TextView
,它会给我一个NullPointerException
:
HelpActivity.java
private final class HelpButtonListener implements OnClickListener {
public void onClick(View v) {
Intent mainToHelpIntent = new Intent(MainActivity.this, HelpActivity.class);
startActivity(mainToHelpIntent);
}
}
public class HelpActivity extends RoboActivity {
@InjectView(R.id.helpTextView)
private TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
helpTextView.setText("Some helpful stuff..");
setContentView(R.layout.activity_help);
}
}
以下是我在单击“帮助”按钮并尝试在活动\u Help.xml
版面资源上创建的文本视图中设置文本时遇到的错误:
05-16 18:00:52.591: E/AndroidRuntime(9880): FATAL EXCEPTION: main
05-16 18:00:52.591: E/AndroidRuntime(9880): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wickedlynotsmart.myfirstapp/com.wickedlynotsmart.myfirstapp.activity.HelpActivity}: java.lang.NullPointerException
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.os.Handler.dispatchMessage(Handler.java:99)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.os.Looper.loop(Looper.java:137)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.ActivityThread.main(ActivityThread.java:5041)
05-16 18:00:52.591: E/AndroidRuntime(9880): at java.lang.reflect.Method.invokeNative(Native Method)
05-16 18:00:52.591: E/AndroidRuntime(9880): at java.lang.reflect.Method.invoke(Method.java:511)
05-16 18:00:52.591: E/AndroidRuntime(9880): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-16 18:00:52.591: E/AndroidRuntime(9880): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-16 18:00:52.591: E/AndroidRuntime(9880): at dalvik.system.NativeStart.main(Native Method)
05-16 18:00:52.591: E/AndroidRuntime(9880): Caused by: java.lang.NullPointerException
05-16 18:00:52.591: E/AndroidRuntime(9880): at com.wickedlynotsmart.myfirstapp.activity.HelpActivity.onCreate(HelpActivity.java:22)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.Activity.performCreate(Activity.java:5104)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
05-16 18:00:52.591: E/AndroidRuntime(9880): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
05-16 18:00:52.591: E/AndroidRuntime(9880): ... 11 more
有人能帮我理解为什么我会犯这个错误吗
谢谢。首先将内容设置为活动。然后初始化textview。然后将文本设置为textview。您尚未初始化textview。因此您得到了NullPointerException
private TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_help); //set content tot eh activity
helpTextView = (TextView) findViewById(R.id.textview); // initialize textview
helpTextView.setText("Some helpful stuff.."); //set text to textview
}
应该是这样的:
setContentView(R.layout.activity_help);
TextView helpTextView = (TextView)findViewById(R.id.helpTextView);
helpTextView.setText("Some helpful stuff..");
首先将内容设置为活动。然后初始化textview。然后将文本设置为textview。您尚未初始化textview。因此您得到了NullPointerException
private TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_help); //set content tot eh activity
helpTextView = (TextView) findViewById(R.id.textview); // initialize textview
helpTextView.setText("Some helpful stuff.."); //set text to textview
}
应该是这样的:
setContentView(R.layout.activity_help);
TextView helpTextView = (TextView)findViewById(R.id.helpTextView);
helpTextView.setText("Some helpful stuff..");
//这是链接
//这是链接
将内容设置为“活动”,然后通过视图层次结构的findViewById初始化textview,然后将文本设置为textview。您的textview未初始化,因此您将获得NullPointerException
private TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_help); //set content tot eh activity
helpTextView = (TextView) findViewById(R.id.textview); // initialize textview
helpTextView.setText("Some helpful stuff.."); //set text to textview
}
根据这个链接。使用机器人世界可以如下
private TextView helpTextView;
@InjectView(R.id.textview) TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_help); //set content tot eh activity
helpTextView.setText("Some helpful stuff.."); //set text to textview
}
将内容设置为“活动”,然后通过视图层次结构的findViewById初始化textview,然后将文本设置为textview。您的textview未初始化,因此您将获得NullPointerException
private TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_help); //set content tot eh activity
helpTextView = (TextView) findViewById(R.id.textview); // initialize textview
helpTextView.setText("Some helpful stuff.."); //set text to textview
}
根据这个链接。使用机器人世界可以如下
private TextView helpTextView;
@InjectView(R.id.textview) TextView helpTextView;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_help); //set content tot eh activity
helpTextView.setText("Some helpful stuff.."); //set text to textview
}
@blackbelt:我在HelpActivity
的onCreate
方法中添加了super.onCreate
调用,但它仍然不起作用,并显示相同的NullPointerException
错误。@blackbelt:我错误地单击了“编辑到您的注释器”,因为当时我想单击“注释”对您的答案进行注释,我取消了编辑并保存了所有我可以保存的内容,但我无法再次看到您的答案。请检查我的答案,如果有,请随时询问questions@blackbelt:我在HelpActivity
的onCreate
方法中添加了super.onCreate
调用,但它仍然不起作用,并显示相同的NullPointerException
错误。@blackbelt:我错误地点击了你的注释的编辑,因为当我想点击评论对你的答案进行评论时,我取消了编辑并保存了所有我能保存的内容,但我无法再次看到你的答案。请检查我的答案,并随时询问是否有任何问题Shello首先设置了内容,然后你将获得TextView的实例哦,亲爱的,我在干什么?谢谢。您好,首先设置setcontent,然后您将获得textviewOh天哪,我在做什么?谢谢。是的,在第一种情况下,您正在创建动态文本视图,然后将其添加到视图中。是的,它会起作用的。但在第二种情况下,要从布局xml文件访问textview或任何小部件,您应该在读取之前首先在setContentView中设置xml文件;机器人行动小心it@Abhi你不读文本视图。您可以初始化textview。我已经编辑了你答案的那部分,因为它是misleading@Raghunandan非常感谢。如果你不留下这个邀请,你能来吗:)@Abhi我被屏蔽了好几天,现在不能聊天了。SorryYes在第一种情况下,您正在创建动态文本视图,然后将其添加到视图中。是的,它会起作用的。但在第二种情况下,要从布局xml文件访问textview或任何小部件,您应该在读取之前首先在setContentView中设置xml文件;机器人行动小心it@Abhi你不读文本视图。您可以初始化textview。我已经编辑了你答案的那部分,因为它是misleading@Raghunandan非常感谢。如果你不留下这个邀请,你能来吗:)@Abhi我被屏蔽了好几天,现在不能聊天了。SorryIt将解释RoboJuice@pawanyadav,你能解释为什么会发生这种情况吗?因为我没有尝试过robospice myselfRoboJuice是google框架,它避免了依赖注入。此链接将详细解释。它将解释RoboJuice@pawanyadav,你能解释为什么会发生这种情况吗?因为我没有尝试过robospice myselfRoboJuice是谷歌框架,它避免了依赖注入。此链接将详细解释。