Question

我正在尝试在按钮单击侦听器上滑动图像。我正在采取新的布局。每个布局包含不同的全屏图像。在单击按钮时，应显示下一个布局。这是我的代码。

public class ImageSlider extends Activity {

Button b, c, d;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_image_slider);

     b = (Button)findViewById(R.id.image);
    b.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

            setContentView(R.layout.image1);

        }
    });

     c = (Button)findViewById(R.id.image1btn);
        c.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                setContentView(R.layout.image2);
            }
        }); 

         d = (Button)findViewById(R.id.image2btn);
        d.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                setContentView(R.layout.activity_image_slider);
            }
        });
}

但是即使正确地初始化所有按钮，我也会得到Null指针异常。这是错误日志。请帮忙。

10-25 12:49:07.813: E/AndroidRuntime(13489): FATAL EXCEPTION: main
10-25 12:49:07.813: E/AndroidRuntime(13489): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fouractivities/com.example.fouractivities.ImageSlider}: java.lang.NullPointerException
10-25 12:49:07.813: E/AndroidRuntime(13489): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
10-25 12:49:07.813: E/AndroidRuntime(13489):at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
10-25 12:49:07.813: E/AndroidRuntime(13489):at android.app.ActivityThread.access$600(ActivityThread.java:123)
10-25 12:49:07.813: E/AndroidRuntime(13489):at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
10-25 12:49:07.813: E/AndroidRuntime(13489):at android.os.Handler.dispatchMessage(Handler.java:99)
10-25 12:49:07.813: E/AndroidRuntime(13489):at android.os.Looper.loop(Looper.java:137)
10-25 12:49:07.813: E/AndroidRuntime(13489):at android.app.ActivityThread.main(ActivityThread.java:4424)
10-25 12:49:07.813: E/AndroidRuntime(13489):at java.lang.reflect.Method.invokeNative(Native Method)
10-25 12:49:07.813: E/AndroidRuntime(13489):at java.lang.reflect.Method.invoke(Method.java:511)
10-25 12:49:07.813: E/AndroidRuntime(13489):at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
10-25 12:49:07.813: E/AndroidRuntime(13489):at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
10-25 12:49:07.813: E/AndroidRuntime(13489):at dalvik.system.NativeStart.main(Native Method)

主要活动的XML文件

<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=".ImageSlider" >

<Button
    android:id="@+id/image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="185dp"
    android:text="@string/image" />

第一张图片的XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ImageView
    android:id="@+id/imageView1"
    android:layout_width="150dp"
    android:layout_height="300dp"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentTop="true"
    android:src="@drawable/a" />

<Button
    android:id="@+id/image1btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_centerVertical="true"
    android:text="Next" />

Answer 1

这是错误的

您不得使用设置内容视图进行图像切换，

当你将setContentView设置为另一个布局时，按钮将为null

将它用于所有人......

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<ImageView
     android:id="@+id/imageView1"
     android:layout_width="150dp"
     android:layout_height="300dp"
     android:layout_alignParentBottom="true"
     android:layout_alignParentLeft="true"
     android:layout_alignParentRight="true"
     android:layout_alignParentTop="true"
     android:src="@drawable/a" />
</RelativeLayout>

你可以在MainActivity中使用类似的东西

public class MainActivity extends Activity {


int[] pic_num = {R.drawable.img1,
        R.drawable.img2,
        R.drawable.img3};
int i = 1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    final ImageView iv = (ImageView) findViewById(R.id.imageView1);
    iv.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

            iv.setImageResource(pic_num[i+1]);
            i ++;
            if(i == 3){
                i = 1;
            }
        }
    });
}

}

Answer 2

试试这个..

在activity_image_slider.xml中没有Button image1btn和ImageButton imageView1这就是为什么NPE来了

使用ViewPager

https://github.com/chiuki/android-swipe-image-viewer

Answer 3

我认为你首先不匹配布局。设置 setContentView（R.layout.main_activity）而不是 setContentView（R.layout.activity_image_slider）;

super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity) //respective layout here
b = (Button)findViewById(R.id.image);

由于布局不匹配，各个布局的ID缺失并且通过NPE

无法找到Null指针异常

3 个答案: