它没有打开以下活动并给我错误。如何在活动加载之前打开imageview。
// Menu.java
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
public class Menu extends Activity {
ImageView status,contact,submit,day;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
status = (ImageView) findViewById(R.id.status_id);
day = (ImageView) findViewById(R.id.day_id);
submit = (ImageView) findViewById(R.id.submit_id);
contact = (ImageView) findViewById(R.id.contact_id);
setContentView(R.layout.menu);
status.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Intent intent = new Intent(Menu.this,StatusMenu.class);
startActivity(intent);
}
});
day.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Intent intent = new Intent(Menu.this,StatusMenu.class);
startActivity(intent);
}
});
submit.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Intent intent = new Intent(Menu.this,StatusMenu.class);
startActivity(intent);
}
});
contact.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Intent intent = new Intent(Menu.this,StatusMenu.class);
startActivity(intent);
}
});
}
}
// logcat的
05-20 01:10:36.812: D/gralloc_goldfish(643): Emulator without GPU emulation detected.
05-20 01:10:40.133: D/dalvikvm(643): GC_CONCURRENT freed 478K, 9% free 32086K/34951K, paused 31ms+6ms
05-20 01:10:40.563: D/dalvikvm(643): GC_CONCURRENT freed 5K, 3% free 34002K/34951K, paused 27ms+9ms
05-20 01:10:40.822: D/dalvikvm(643): GC_FOR_ALLOC freed 3K, 1% free 35278K/35591K, paused 61ms
05-20 01:10:41.042: D/dalvikvm(643): GC_FOR_ALLOC freed 1K, 1% free 36562K/36871K, paused 48ms
05-20 01:10:41.134: D/AndroidRuntime(643): Shutting down VM
05-20 01:10:41.134: W/dalvikvm(643): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
05-20 01:10:41.153: E/AndroidRuntime(643): FATAL EXCEPTION: main
05-20 01:10:41.153: E/AndroidRuntime(643): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.status.what/com.status.what.Menu}: java.lang.NullPointerException
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.ActivityThread.access$600(ActivityThread.java:122)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.os.Handler.dispatchMessage(Handler.java:99)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.os.Looper.loop(Looper.java:137)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-20 01:10:41.153: E/AndroidRuntime(643): at java.lang.reflect.Method.invokeNative(Native Method)
05-20 01:10:41.153: E/AndroidRuntime(643): at java.lang.reflect.Method.invoke(Method.java:511)
05-20 01:10:41.153: E/AndroidRuntime(643): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-20 01:10:41.153: E/AndroidRuntime(643): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-20 01:10:41.153: E/AndroidRuntime(643): at dalvik.system.NativeStart.main(Native Method)
05-20 01:10:41.153: E/AndroidRuntime(643): Caused by: java.lang.NullPointerException
05-20 01:10:41.153: E/AndroidRuntime(643): at com.status.what.Menu.onCreate(Menu.java:26)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.Activity.performCreate(Activity.java:4465)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-20 01:10:41.153: E/AndroidRuntime(643): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
05-20 01:10:41.153: E/AndroidRuntime(643): ... 11 more
05-20 01:15:41.312: I/Process(643): Sending signal. PID: 643 SIG: 9
// menu.xml文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:layout_marginTop="-40dp"
android:background="@drawable/green" >
<ScrollView
android:scrollbars="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/ScrollView">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:layout_gravity="center_vertical"
android:orientation="vertical">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical">
<ImageView
android:layout_width="130dp"
android:layout_height="130dp"
android:id="@+id/status_id"
android:src="@drawable/status_form" />
<TextView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_gravity="center"
android:textSize="15sp"
android:textColor="#FFFFFF"
android:id="@+id/satus_text"
android:text=" Status Outfits" />
</LinearLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:orientation="horizontal"
android:paddingTop="10dp" >
<ImageView
android:id="@+id/submit_id"
android:layout_width="130dp"
android:layout_height="130dp"
android:layout_alignParentRight="true"
android:layout_alignTop="@+id/day_id"
android:paddingRight="10dp"
android:src="@drawable/submit_form" />
<ImageView
android:id="@+id/day_id"
android:layout_width="130dp"
android:layout_height="130dp"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:src="@drawable/day_form" />
</RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:orientation="horizontal"
android:paddingTop="2dp" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:textSize="15sp"
android:textColor="#FFFFFF"
android:id="@+id/day_text"
android:text=" Status of the Day" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:textSize="15sp"
android:textColor="#FFFFFF"
android:id="@+id/submit_text"
android:text=" Share Your Status " />
</RelativeLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:paddingTop="10dp"
android:orientation="vertical">
<ImageView
android:layout_width="130dp"
android:layout_height="130dp"
android:id="@+id/contact_id"
android:layout_gravity="center_horizontal"
android:src="@drawable/contact_form" />
<TextView
android:id="@+id/contact_text"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:layout_gravity="center"
android:layout_marginTop="-15dp"
android:text="Connect with Developer"
android:textColor="#FFFFFF"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
</ScrollView>
</LinearLayout>
答案 0 :(得分：0)
findViewById()会返回一个视图，如果它存在于您setContentView()中提供的布局中，否则会返回null以及发生的事情。
在实例化imageViews之前设置内容视图。
更改此部分：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
status = (ImageView) findViewById(R.id.status_id);
day = (ImageView) findViewById(R.id.day_id);
submit = (ImageView) findViewById(R.id.submit_id);
contact = (ImageView) findViewById(R.id.contact_id);
setContentView(R.layout.menu);
到此：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.menu); //set the contentView before finding Views using findViewByID
status = (ImageView) findViewById(R.id.status_id);
day = (ImageView) findViewById(R.id.day_id);
submit = (ImageView) findViewById(R.id.submit_id);
contact = (ImageView) findViewById(R.id.contact_id);
答案 1 :(得分：0)
您应该将setContentView（R.layout.menu）放在super.onCreate（savedInstanceState）下面并尝试
答案 2 :(得分：0)
您必须加载布局并获取对该视图的引用。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.menu); //* this line must be here!:)
status = (ImageView) findViewById(R.id.status_id);
day = (ImageView) findViewById(R.id.day_id);
submit = (ImageView) findViewById(R.id.submit_id);
contact = (ImageView) findViewById(R.id.contact_id);
... ... ...