问题描述
- 新手,刚开始学习Android,遇到难题(生命周期函数),求助啊,望大神们支招。。。
-
AndroidManifest.xml中:<?xml version="1.0" encoding="utf-8"?>
package="com.yang.lifecyle"
android:versionCode="1"
android:versionName="1.0" ><uses-sdk android:minSdkVersion="8" android:targetSdkVersion="21" /> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name="com.yang.lifecyle.MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name="com.yang.lifecyle.OtherActivity" android:label="name"> </activity> </application>
MainActivity.java
package com.yang.lifecyle;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;public class MainActivity extends ActionBarActivity {
private Button button; private ButtonListener buttonListener; protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); buttonListener=new ButtonListener(); button=(Button)findViewById(R.id.button); button.setOnClickListener(buttonListener); } class ButtonListener implements OnClickListener{ @Override public void onClick(View v) { // TODO Auto-generated method stub Intent intent=new Intent(); intent.setClass(MainActivity.this, OtherActivity.class); intent.putExtra("com.yang.lifecyle.Age", 20); startActivity(intent); } }
fragment_main
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.yang.lifecyle.MainActivity$PlaceholderFragment" ><Button android:id="@+id/button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="start" />
**
OtherActivity.java**package com.yang.lifecyle;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.TextView;public class OtherActivity extends ActionBarActivity{
private TextView textView;
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.other_activity);
Intent intent=getIntent();
int age=intent.getIntExtra("com.yang.lifecyle.Age",10);
textView=(TextView)findViewById(R.id.textView);
textView.setText("age "+age);}
}
other_activity.xml
<?xml version="1.0" encoding="utf-8"?>
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" ><TextView android:id="@+id/textView" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="第二个Activity" />
LogCat
08-07 13:32:52.033: W/dalvikvm(391): threadid=1: thread exiting with uncaught exception (group=0x40015560)
08-07 13:32:52.133: E/AndroidRuntime(391): FATAL EXCEPTION: main
08-07 13:32:52.133: E/AndroidRuntime(391): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yang.lifecyle/com.yang.lifecyle.MainActivity}: java.lang.NullPointerException
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1638)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:928)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.os.Handler.dispatchMessage(Handler.java:99)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.os.Looper.loop(Looper.java:123)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.ActivityThread.main(ActivityThread.java:3647)
08-07 13:32:52.133: E/AndroidRuntime(391): at java.lang.reflect.Method.invokeNative(Native Method)
08-07 13:32:52.133: E/AndroidRuntime(391): at java.lang.reflect.Method.invoke(Method.java:507)
08-07 13:32:52.133: E/AndroidRuntime(391): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-07 13:32:52.133: E/AndroidRuntime(391): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-07 13:32:52.133: E/AndroidRuntime(391): at dalvik.system.NativeStart.main(Native Method)
08-07 13:32:52.133: E/AndroidRuntime(391): Caused by: java.lang.NullPointerException
08-07 13:32:52.133: E/AndroidRuntime(391): at com.yang.lifecyle.MainActivity.onCreate(MainActivity.java:20)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-07 13:32:52.133: E/AndroidRuntime(391): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1586)
08-07 13:32:52.133: E/AndroidRuntime(391): ... 11 more
08-07 13:32:52.153: W/ActivityManager(61): Force finishing activity com.yang.lifecyle/.MainActivity
08-07 13:32:52.659: W/ActivityManager(61): Activity pause timeout for HistoryRecord{406fee18 com.yang.lifecyle/.MainActivity}
08-07 13:33:03.612: W/ActivityManager(61): Activity destroy timeout for HistoryRecord{406fee18 com.yang.lifecyle/.MainActivity}
08-07 13:33:05.007: W/ActivityManager(61): Activity idle timeout for HistoryRecord{408b0e00 com.yang.lifecyle/.MainActivity}
解决方案
一开始就错了,看这个demo,貌似看过,你应该也是对着敲的吧。public class MainActivity extends ActionBarActivity,你这里不应该集成ActionBarActivity,应该继承Activity,当然这不是你的,新版ADT,如果不动脑筋,建工程一路next下来,就会继承这个,还生成一堆废代码,所有建工程时注意下,主题那里选择none,Activity类型选择empty,不知道能不能解决你的问题,你可以改成继承Activity试试。
解决方案二:
一开始就错了,看这个demo,貌似看过,你应该也是对着敲的吧。public class MainActivity extends ActionBarActivity,你这里不应该集成ActionBarActivity,应该继承Activity,当然这不是你的,新版ADT,如果不动脑筋,建工程一路next下来,就会继承这个,还生成一堆废代码,所有建工程时注意下,主题那里选择none,Activity类型选择empty,不知道能不能解决你的问题,你可以改成继承Activity试试。
解决方案三:
网络不好,多点几下,就发这么多,还不能删除,也是醉了
解决方案四:
android使用接口的话好像只能使用activity自己做接口,你的接口似乎有错啊。。。建议还是用内部匿名类吧。。。用接口看起来很怪异。。
用接口的话这么用:在定义MainActivity时这么定。public Class MainActivity extends Activity implements onClickListener{
.....//你的代码
}
这时导入android使用接口的话好像只能使用activity自己做接口,你的接口似乎有错啊。。。建议还是用内部匿名类吧。。。用接口看起来很怪异。。
用接口的话这么用:在定义MainActivity时这么定。public Class MainActivity extends Activity implements onClickListener{
button.setOnclickListener(this);
}
这时导入一个重写的方法。。。public void onClick(View v){
这个时候就是你接口里面的方法了。。。。
}
用内部类的话:button.setOnclickListener(new OnclickListener(){
public void onClick(View v){
接口方法里面的代码
}
}); 你试试看吧。。。。
解决方案五: