java - 不幸的是应用程序已停止工作

Question

我是 Android 应用程序开发的新手。我正在做这个教程应用程序。这是一个非常简单的应用程序。它从计数器中加一减一。当我在模拟器中运行它时，它说“不幸的是教程已停止工作。”代码中没有错误。 API 级别是 17。请帮助我。

Java 代码:

public class Startingpoint extends Activity {
  int counter=0;   
  Button add,subtract; 
  TextView display; 

  @Override    
  protected void onCreate(Bundle savedInstanceState) {    
    super.onCreate(savedInstanceState);    
    setContentView(R.layout.startingpoint);    
    add = (Button) findViewById(R.id.bAdd);    
    subtract= (Button) findViewById(R.id.bSubtract);   
    display= (Button) findViewById(R.id.text);    
    add.setOnClickListener(new View.OnClickListener() {

      @Override   
      public void onClick(View v) {   
        counter++;  
        display.setText("The total is " + counter);   
      }   
    });   

    subtract.setOnClickListener(new View.OnClickListener() {
      @Override 
      public void onClick(View v) {
        counter--;
        display.setText("The total is " + counter);
      }

    });
  }

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.startingpoint, menu);
    return true;
  }
}

xml 中的布局代码:

<?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" >  

    <TextView android:id="@+id/text"    
              android:layout_width="wrap_content"   
              android:layout_height="wrap_content"
              android:text="Your total is 0"
              android:textSize="35dp"
              android:layout_gravity="center"
              android:gravity="center"/>

    <Button   android:layout_width="250dp"
              android:layout_height="wrap_content"
              android:text="Add One" 
              android:layout_gravity="center" 
              android:textSize="25dp"
              android:id="@+id/bAdd"/>

     <Button  android:layout_width="250dp"
              android:layout_height="wrap_content"
              android:text="Subtract One" 
              android:layout_gravity="center" 
              android:textSize="25dp"
              android:id="@+id/bSubtract"/>
</LinearLayout>

这是日志:

03-02 02:45:10.730: D/AndroidRuntime(780): Shutting down VM
03-02 02:45:10.730: W/dalvikvm(780): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
03-02 02:45:10.750: E/AndroidRuntime(780): FATAL EXCEPTION: main
03-02 02:45:10.750: E/AndroidRuntime(780): java.lang.RuntimeException: Unable to start activity ComponentInfo{tutorial.example.tutorial/tutorial.example.tutorial.Startingpoint}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.os.Looper.loop(Looper.java:137)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.main(ActivityThread.java:5041)
03-02 02:45:10.750: E/AndroidRuntime(780):  at java.lang.reflect.Method.invokeNative(Native Method)
03-02 02:45:10.750: E/AndroidRuntime(780):  at java.lang.reflect.Method.invoke(Method.java:511)
03-02 02:45:10.750: E/AndroidRuntime(780):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-02 02:45:10.750: E/AndroidRuntime(780):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-02 02:45:10.750: E/AndroidRuntime(780):  at dalvik.system.NativeStart.main(Native Method)
03-02 02:45:10.750: E/AndroidRuntime(780): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
03-02 02:45:10.750: E/AndroidRuntime(780):  at tutorial.example.tutorial.Startingpoint.onCreate(Startingpoint.java:22)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.Activity.performCreate(Activity.java:5104)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-02 02:45:10.750: E/AndroidRuntime(780):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
03-02 02:45:10.750: E/AndroidRuntime(780):  ... 11 more

Answer 1

display= (Button) findViewById(R.id.text);

应该是

display= (TextView) findViewById(R.id.text);

由于 display 应该引用一个 TextView 实例，但是您明确地转换为一个 Button，而这些是 不兼容的类型。