自定义对话框中的NPE

时间：2014-06-09 14:46:21

标签： java android

我创建了一个带有两个按钮的活动，根据点击的按钮类型，将显示一个自定义对话框

我为对话框

创建了一个xml文件

dialog.xml 

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:id="@+id/lv_dialog"
    android:background="#FF0000"
    >
    <TextView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="# Do you know?"
          android:layout_gravity="center"
         android:textSize="25px"
         android:layout_marginTop="10px"
                />
    <TextView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="THE FACT IS DISPLAYED HERE"
          android:layout_gravity="center"
         android:textSize="30px"
         android:layout_marginTop="10px"
         android:id="@+id/txtfact"
                />

    <TextView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="THE ANSWER STATUS IS DISPLAYED HERE"
          android:layout_gravity="center"
         android:textSize="32px"
         android:textColor="#FFFFFF"
         android:layout_marginTop="10px"
         android:id="@+id/txtanswer"
                />
    <TextView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="THE SCORE IS DISPLAYED HERE"
          android:layout_gravity="center"
         android:textSize="32px"
         android:textColor="#FFFFFF"
         android:layout_marginTop="10px"
         android:id="@+id/txtscore"
                />
    <Button
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="GOTO NEXT QUESTION"
        android:layout_gravity="center"
       android:textColor="#FFFFFF"
       android:layout_marginTop="20px"
       android:id="@+id/btngotonext"
       />

     </LinearLayout>

活动主要是

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    >
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="CORRECT CHOICE"
        android:id="@+id/btncorrect"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="WRONG CHOICE"
        android:id="@+id/btnwrong"
        />

</LinearLayout>

主要课程是：

package com.example.custom_fifa_dialog;

import android.os.Bundle;
import android.app.Activity;
import android.app.Dialog;
import android.graphics.Color;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

    public class MainActivity extends Activity {

        Button btncorrect,btnwrong,btngotonext;
        LinearLayout lv_dialog;
        Dialog dialog;
        databasemanager dbm;
        String s="";
        TextView txtfact,txtanswer,txtscore;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            dbm=new databasemanager(this);
            dialog=new Dialog(this);

            btncorrect=(Button) findViewById(R.id.btncorrect);
            btnwrong=(Button) findViewById(R.id.btnwrong);
            lv_dialog=(LinearLayout) findViewById(R.id.lv_dialog);

            btncorrect.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    lv_dialog.setBackgroundColor(Color.parseColor("#008000"));
                    dialog.setContentView(R.layout.dialog);
                    txtfact=(TextView) dialog.findViewById(R.id.txtfact);
                    txtanswer=(TextView) dialog.findViewById(R.id.txtanswer);
                    txtscore=(TextView) dialog.findViewById(R.id.txtscore);
                    btngotonext=(Button) dialog.findViewById(R.id.btngotonext);
                    int random=1 + (int)(Math.random() * ((736 -1) + 1));
                    dialog.setTitle("RESULT");
                    Toast.makeText(getApplicationContext(), ""+random,Toast.LENGTH_SHORT).show();
                     s=dbm.getdouknow(random);
                    txtfact.setText(s);
                    txtanswer.setText("CORRECT ANSWER");
                    txtscore.setText("SCORE:25");
                    btngotonext.setOnClickListener(new OnClickListener() {

                        @Override
                        public void onClick(View v) {
                            dialog.dismiss();

                        }
                    });
                    dialog.setCancelable(false);
                       dialog.show();


                }
            });
            btnwrong.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    lv_dialog.setBackgroundColor(Color.parseColor("#FF0000"));
                    dialog.setContentView(R.layout.dialog);
                    txtfact=(TextView) dialog.findViewById(R.id.txtfact);
                    txtanswer=(TextView) dialog.findViewById(R.id.txtanswer);
                    txtscore=(TextView) dialog.findViewById(R.id.txtscore);
                    btngotonext=(Button) dialog.findViewById(R.id.btngotonext);
                    int random=1 + (int)(Math.random() * ((736 -1) + 1));
                    dialog.setTitle("RESULT");
                    Toast.makeText(getApplicationContext(), ""+random,Toast.LENGTH_SHORT).show();
                     s=dbm.getdouknow(random);
                    txtfact.setText(s);
                    txtanswer.setText("WRONG ANSWER");
                    txtscore.setText("SCORE:0");
                    btngotonext.setOnClickListener(new OnClickListener() {

                        @Override
                        public void onClick(View v) {
                            dialog.dismiss();

                        }
                    });
                    dialog.setCancelable(false);
                      dialog.show();
                }
            });
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.main, menu);
            return true;
        }

    }

我在设置背景颜色的行处获得NPE：

logcat的：

06-09 10:45:00.660: E/AndroidRuntime(18253): FATAL EXCEPTION: main
06-09 10:45:00.660: E/AndroidRuntime(18253): Process: com.example.custom_fifa_dialog, PID: 18253
06-09 10:45:00.660: E/AndroidRuntime(18253): java.lang.NullPointerException
06-09 10:45:00.660: E/AndroidRuntime(18253):    at com.example.custom_fifa_dialog.MainActivity$1.onClick(MainActivity.java:38)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at android.view.View.performClick(View.java:4438)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at android.view.View$PerformClick.run(View.java:18422)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at android.os.Handler.handleCallback(Handler.java:733)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at android.os.Handler.dispatchMessage(Handler.java:95)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at android.os.Looper.loop(Looper.java:136)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at android.app.ActivityThread.main(ActivityThread.java:5017)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at java.lang.reflect.Method.invokeNative(Native Method)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at java.lang.reflect.Method.invoke(Method.java:515)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-09 10:45:00.660: E/AndroidRuntime(18253):    at dalvik.system.NativeStart.main(Native Method)

请帮忙！

3 个答案:

答案 0 :(得分：1)

当您致电lv_dialog=(LinearLayout) findViewById(R.id.lv_dialog);时，您正在当前活动上调用findViewById()，而不是对话框。由于具有标识lv_dialog的LinearLayout位于Dialog的布局中而不是Activity，因此将返回null。

在致电dialog.setContentView(R.layout.dialog);之前，您的对话框布局甚至不会膨胀。

解决这个问题的一种方法是在设置Dialog的布局之前不检索LinearLayout，如下所示：

btncorrect.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
        dialog.setContentView(R.layout.dialog);
        lv_dialog=(LinearLayout) dialog.findViewById(R.id.lv_dialog);
        lv_dialog.setBackgroundColor(Color.parseColor("#008000"));
        // ...
    }
}

答案 1 :(得分：0)

您需要在setContent for dialog后调用此行。在开始时，您将获得空引用。

lv_dialog=(LinearLayout) findViewById(R.id.lv_dialog);

答案 2 :(得分：0)

在您的活动lv_dialog中，dialog.xml文件不属于activity_main。 所以 设置对话框布局后，将lv_dialog的实例设为 改变这个

lv_dialog.setBackgroundColor(Color.parseColor("#008000"));
dialog.setContentView(R.layout.dialog);

到

  dialog.setContentView(R.layout.dialog);
lv_dialog=(LinearLayout) dialog.findViewById(R.id.lv_dialog);
 lv_dialog.setBackgroundColor(Color.parseColor("#008000"));

并删除

lv_dialog=(LinearLayout) findViewById(R.id.lv_dialog);

来自OnCreate函数

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