如何使用类和实例将变量传递给 findViewById 方法？

Question

我最近一直在尝试在android工作室制作这个井字游戏，我对android工作室和java只有基本的了解，所以我想通过制作类和对象来完成这个应用程序，但是每当我尝试运行我的应用程序时，应用程序崩溃了，我不知道它正确编译的代码有什么问题，有人可以帮我吗？

这是 logcat window:

11-04 23:48:20.249 4534-4534/? I/zygote: Not late-enabling -Xcheck:jni (already on)
11-04 23:48:20.258 4534-4534/? W/zygote: Unexpected CPU variant for X86 using defaults: x86
11-04 23:48:20.480 4534-4534/com.example.home.tictactoe I/InstantRun: starting instant run server: is main process
11-04 23:48:20.845 4534-4534/com.example.home.tictactoe D/AndroidRuntime: Shutting down VM
11-04 23:48:20.851 4534-4534/com.example.home.tictactoe E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.home.tictactoe, PID: 4534
                                                                          java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.home.tictactoe/com.example.home.tictactoe.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewPropertyAnimator android.widget.ImageView.animate()' on a null object reference
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                                              at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                              at android.os.Looper.loop(Looper.java:164)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:6541)
                                                                              at java.lang.reflect.Method.invoke(Native Method)
                                                                              at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                                                           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewPropertyAnimator android.widget.ImageView.animate()' on a null object reference
                                                                              at com.example.home.tictactoe.MainActivitypawn.hideObj(MainActivity.java:45)
                                                                              at com.example.home.tictactoe.MainActivity.onCreate(MainActivity.java:53)
                                                                              at android.app.Activity.performCreate(Activity.java:6975)
                                                                              at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
                                                                              at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                              at android.os.Looper.loop(Looper.java:164) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:6541) 
                                                                              at java.lang.reflect.Method.invoke(Native Method) 
                                                                              at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

这是我的 MainActivity.java 文件

    package com.example.home.tictactoe;

    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.widget.Button;
    import android.widget.ImageView;

    public class MainActivity extends AppCompatActivity {

        public void clickButton(View view){

            Log.i("test","working");


        }




        @Override
        protected void onCreate(Bundle savedInstanceState) {


            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);




            class pawn{


                int resID = 0;

                ImageView object2 = (ImageView) findViewById(resID);

                public void showObj()
                {
                    object2.animate().alpha(1f).setDuration(1000);//add code here to change alpha of object
                }
                public void hideObj()
                {
                    object2.animate().alpha(0f).setDuration(1000);
                }

            }
            final pawn x_11 = new pawn();
            final pawn zero_11 = new pawn();
            x_11.resID = R.id.x11;
            zero_11.resID=R.id.zero11;
            x_11.hideObj();

   }

}

见图：

Answer 1

ImageView object2 = (ImageView) findViewById(resID); 在创建 pawn 对象时被调用。此时您还没有为您的对象设置 resId，因此它将为 0。这导致 object2 到 null。

您可以这样更改 class：

class pawn {
      int resID = 0;

      ImageView object2;

      public pawn(int resID) {
          this.resID = resID;
          object2 = (ImageView) findViewById(resID)
      }

      public void showObj()
      {
          object2.animate().alpha(1f).setDuration(1000);//add code here to change alpha of object
      }

      public void hideObj()
      {
          object2.animate().alpha(0f).setDuration(1000);
      }
}

那就用吧

pawn x_11 = new pawn(R.id.x11);
x_11.hideObj();

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如何使用类和实例将变量传递给 findViewById 方法？