強制轉換android.widget.TextView

Question

我是android developpement的新手，在嘗試創建可編輯的TextView時遇到了以下異常。

這是異常的完整堆棧跟蹤

09-17 01:25:14.749: E/AndroidRuntime(8436): FATAL EXCEPTION: main
09-17 01:25:14.749: E/AndroidRuntime(8436): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.timer/com.example.timer.TimerHomeActivity}: java.lang.ClassCastException: android.widget.TextView
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.os.Looper.loop(Looper.java:130)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.ActivityThread.main(ActivityThread.java:3687)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at java.lang.reflect.Method.invokeNative(Native Method)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at java.lang.reflect.Method.invoke(Method.java:507)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at dalvik.system.NativeStart.main(Native Method)
09-17 01:25:14.749: E/AndroidRuntime(8436): Caused by: java.lang.ClassCastException: android.widget.TextView
09-17 01:25:14.749: E/AndroidRuntime(8436):     at com.example.timer.TimerHomeActivity.onCreate(TimerHomeActivity.java:23)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
09-17 01:25:14.749: E/AndroidRuntime(8436):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
09-17 01:25:14.749: E/AndroidRuntime(8436):     ... 11 more

這是代碼：

public class TimerHomeActivity extends Activity implements OnClickListener {

   public void onClick(View v) {
     TextView tv = (TextView)findViewById(R.id.timer_1);
     tv.setText("Hi");
   }
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.timer_home);
      Button timer1 = (Button)findViewById(R.id.timer_1);
      timer1.setOnClickListener(this);
   }  
}

Answer 1

檢查您的資源ID。 您將兩次加載相同的資源ID，一次轉換為TextView ，一次轉換為Button ：

TextView tv = (TextView)findViewById(R.id.timer_1);

和

Button timer1 = (Button)findViewById(R.id.timer_1);

它應該對應一個小部件而另一個將拋出ClassCastException 。

由於啟動活動時發生異常，因此導致異常的語句應該是onCreate方法中的語句。 這意味着資源timer_1不是一個Button而是一個TextView （如異常消息中所示，順便說一下，這個消息似乎在你的帖子中被截斷）。