Question

我有2个微调器，基于它的组合，在按钮点击时打开一个新的xml，其中将根据微调器的组合显示图像。

基本上我面临着两个问题。

按钮onClickListner（）不起作用，我评论了该功能并向前推进
image.setImageResource（）无效logcat表示他无法启动活动。

那究竟我做错了什么？

这是主要的活动代码..尝试之前的一切工作完美..但是onclick listner（）崩溃了代码..但是评论prg工作..

try
    {
        /*btn=(Button)this.findViewById(R.id.button);
        System.out.println(btn);
        btn.setOnClickListener(new OnClickListener() {              

            public void onClick(View v) {*/

                if(subtxt.equals("Maths"))
                {
                    if(Integer.parseInt(yeartxt)==1990)
                    {
                        Intent ip = new Intent(MainActivity.this, maths.class);
                        startActivity(ip);
                    }
.
 //the prg executes until start activity perfectly and continues onto maths.class
.

.

这是maths.java中的代码

protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
 ImageView image;
 image = (ImageView) findViewById(R.id.imageView1);
 image.setImageResource(R.drawable.heart_maths);
 setContentView(R.layout.physics);
    }

所有活动都在android mainfest中指定.. 这是日志猫

 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.ActivityThread.access$800(ActivityThread.java:135)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.os.Handler.dispatchMessage(Handler.java:102)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.os.Looper.loop(Looper.java:136)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.ActivityThread.main(ActivityThread.java:5017)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at java.lang.reflect.Method.invokeNative(Native Method)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at java.lang.reflect.Method.invoke(Method.java:515)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at dalvik.system.NativeStart.main(Native Method)
 02-13 00:29:20.908: E/AndroidRuntime(1485): Caused by: java.lang.NullPointerException
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at com.example.subjects.maths.onCreate(maths.java:16)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.Activity.performCreate(Activity.java:5231)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
 02-13 00:29:20.908: E/AndroidRuntime(1485):    ... 11 more

那么这两个错误面临的原因究竟是什么呢？ ??

编辑答案

1) the on clicklistner() error can be avoided by declaring all variables globally in mainactivity.java
2) the image.setImageResource() should be given after setcontentview..

这就是全部。

Answer 1

你错了：首先setContentView(R.layout.physics)以及获得image oncreate()方法之后：

您应格式如下：

 image = (ImageView) findViewById(R.id.imageView1);
 image.setImageResource(R.drawable.heart_maths);
 setContentView(R.layout.physics);

将其替换为

 setContentView(R.layout.physics);
 image = (ImageView) findViewById(R.id.imageView1);
 image.setImageResource(R.drawable.heart_maths);

Answer 2

您需要先设置视图，然后再使用资源。将行setContentView(R.layout.physics);移到顶部。

protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
 setContentView(R.layout.physics);
 ImageView image;
 image = (ImageView) findViewById(R.id.imageView1);
 image.setImageResource(R.drawable.heart_maths);

    }

Answer 3

更改此代码

protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
ImageView image;
image = (ImageView) findViewById(R.id.imageView1);
image.setImageResource(R.drawable.heart_maths);
setContentView(R.layout.physics);
}

到

    protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.physics);
ImageView image;
image = (ImageView) findViewById(R.id.imageView1);
image.setImageResource(R.drawable.heart_maths);

}

在按钮上更改xml页面中的图像单击.. android

3 个答案: