Question

我正在处理一段可以使用Menu inflater切换图像的代码，我已经处理过代码但是只要我点击按钮就会给我强制关闭错误。这是我的代码：

@Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // TODO Auto-generated method stub
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // TODO Auto-generated method stub
        switch (item.getItemId()) {
        case R.id.cameraa:
            Toast.makeText(this, "Start Camera!", Toast.LENGTH_LONG).show();
            break;

        case R.id.gallery:
         Toast.makeText(this, "this is gallery!", Toast.LENGTH_LONG).show();
        break;


    public boolean onOptionsItemSelected(MenuItem item) {
        // TODO Auto-generated method stub
        switch (item.getItemId()) {


    case R.id.ghost_gallery:
            switcher.showNext();
break
            }
            return true;
        }

main.xml中

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
 <ViewSwitcher
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" >

        <FrameLayout
            android:id="@+id/frame"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >

        <ImageView
            android:id="@+id/imageView"
            android:layout_width="fill_parent"
            android:layout_height="match_parent"
            android:scaleType="matrix"
            android:src="@drawable/banana" />
        </FrameLayout>

        <FrameLayout
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >

        <ImageView
            android:id="@+id/imageView"
            android:layout_width="fill_parent"
            android:layout_height="match_parent"
            android:scaleType="matrix"
            android:src="@drawable/apple" />
        </FrameLayout>
    </ViewSwitcher>

这是我的日志

05-21 03:19:35.733: E/AndroidRuntime(758): FATAL EXCEPTION: main
05-21 03:19:35.733: E/AndroidRuntime(758): java.lang.NullPointerException
05-21 03:19:35.733: E/AndroidRuntime(758):  at org.example.touch.Touch.nextView(Touch.java:188)
05-21 03:19:35.733: E/AndroidRuntime(758):  at org.example.touch.Touch.onOptionsItemSelected(Touch.java:180)
05-21 03:19:35.733: E/AndroidRuntime(758):  at android.app.Activity.onMenuItemSelected(Activity.java:2195)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:730)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:143)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:855)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.view.menu.IconMenuView.invokeItem(IconMenuView.java:532)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.view.menu.IconMenuItemView.performClick(IconMenuItemView.java:122)
05-21 03:19:35.733: E/AndroidRuntime(758):  at android.view.View$PerformClick.run(View.java:8816)
05-21 03:19:35.733: E/AndroidRuntime(758):  at android.os.Handler.handleCallback(Handler.java:587)
05-21 03:19:35.733: E/AndroidRuntime(758):  at android.os.Handler.dispatchMessage(Handler.java:92)
05-21 03:19:35.733: E/AndroidRuntime(758):  at android.os.Looper.loop(Looper.java:123)
05-21 03:19:35.733: E/AndroidRuntime(758):  at android.app.ActivityThread.main(ActivityThread.java:4627)
05-21 03:19:35.733: E/AndroidRuntime(758):  at java.lang.reflect.Method.invokeNative(Native Method)
05-21 03:19:35.733: E/AndroidRuntime(758):  at java.lang.reflect.Method.invoke(Method.java:521)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-21 03:19:35.733: E/AndroidRuntime(758):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-21 03:19:35.733: E/AndroidRuntime(758):  at dalvik.system.NativeStart.main(Native Method)

请帮助我解决这件事.... 最诚挚的问候，

Answer 1

嗯，这很简单：switcher是null。是预期的，因为它在布局中甚至没有id。

Answer 2

你是否在onCreate（）中初始化切换器？

你需要在布局中给它一个id：

android:id="@+id/switcher_view"

在切换器之外的任何方法之外声明ViewSwitcher：

private ViewSwitcher switcher;

然后像这样初始化它（在onCreate（）中）：

switcher = (ViewSwitcher) findViewById(R.id.switcher_view);

Answer 3

您未向ViewSwitcher提供身份证明。此外，您还需要使用findViewById在其他代码中引用它。

Answer 4

我用过

private void showImage() {

        Toast.makeText(Touch.this, " User don't  ", Toast.LENGTH_SHORT);
        ImageView imgView = (ImageView) findViewById(R.id.imageView);
        imgView.setImageResource(mImageIds[image_index]);

    }

    @Override
    public void onClick(View v) {

        switch (v.getId()) {

        case (R.id.previous_btn):

            image_index--;

            if (image_index == -1) {
                image_index = MAX_IMAGE_COUNT - 1;
            }

            showImage();
            break;
}}

对我来说效果很好......

Android Image无法切换

4 个答案: