java - 按钮点击计数器android

Question

好吧，我正在构建一个有 24 个问题的应用程序，每个问题在 24 布局中都有 4 个答案 24 布局中的按钮具有相同的 id 和单击值，我试图计算 24 布局中的每个按钮单击次数，最后一个布局显示单击的每个按钮的结果，但在最后一个布局中应用程序崩溃 这是我正在使用的代码

package com.example.andoid.disctest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class MainActivityresult extends AppCompatActivity {

TextView txtCount;
Button btnCount;
int count = 0;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_activityresult);

    txtCount = (TextView)findViewById(R.id.d_result);


     btnCount.findViewById(R.id.button_d);

    btnCount.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            count ++;
            txtCount.setText(String.valueOf(count));

        }
    });


}

}

12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: FATAL EXCEPTION: main 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: Process: com.example.andoid.disctest, PID: 13188 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.andoid.disctest/com.example.andoid.disctest.MainActivity_result}: java.lang.NullPointerException 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2413) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2471) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.access$900(ActivityThread.java:175) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.os.Looper.loop(Looper.java:146) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5602) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: Caused by: java.lang.NullPointerException 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at com.example.andoid.disctest.MainActivity_result.onCreate(MainActivity_result.java:24) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.Activity.performCreate(Activity.java:5451) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2377) 12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2471)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.access$900(ActivityThread.java:175)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.os.Looper.loop(Looper.java:146)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5602)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)  12-27 20:56:54.169 13188-13188/com.example.andoid.disctest E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method) 

Answer 1

btnCount 未初始化。 您应该替换:

btnCount.findViewById(R.id.button_d);

与:

btnCount = (Button)findViewById(R.id.button_d);