我是android编程的初学者，我正在尝试制作一个简单的Rock，Paper，Scissors应用程序。现在我有三个按钮（摇滚，纸和剪刀）。当用户按下它们时，计算机随机选择摇滚，纸张或剪刀，然后比较它们以查看用户是否赢了。如果用户赢了，那么我希望屏幕右上角的得分计数器增加1.首先我尝试在onCreate方法之外初始化int scoreCount，这导致应用程序无法启动。现在，我在upScore方法中得到一个空指针异常，我正在尝试使用setText用最新的scoreCount更新我的TextView。以下是我的代码。感谢您提供的任何帮助！如果您需要其他信息，请告诉我们！我真的坚持这个！
import android.app.DialogFragment;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
int scoreCount;
TextView scoreView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
scoreCount = 0;
TextView scoreView = (TextView) findViewById(R.id.score);
scoreView.setText("Score: " + scoreCount);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void outcome(View view){
//This function will determine whether the user picked Rock, Paper, or Scissors
//and then randomly have the computer pick Rock, Paper, or Scissors. A dialog will then
//generate to let the user know whether they won or lost.
String[] rpsArray = {"Rock","Paper","Scissors"};
int index = new Random().nextInt(rpsArray.length);
String cpuChoice = rpsArray[index];
String message = "";
int id = view.getId();
switch(id){
case R.id.rock_button:
if(cpuChoice.equals("Rock")){
//Tie
message = "The Computer picked Rock! It's a Tie!";
}
else if(cpuChoice.equals("Paper")){
//You Lose
message = "The Computer picked Paper! You Lose!";
}
else if(cpuChoice.equals("Scissors")){
//You win
message = "The Computer picked Scissors! You Win!";
upScore();
}
break;
case R.id.paper_button:
if(cpuChoice.equals("Paper")){
//Tie
message = "The Computer picked Paper! It's a Tie!";
}
else if(cpuChoice.equals("Scissors")){
//You Lose
message = "The Computer picked Scissors! You Lose!";
}
else if(cpuChoice.equals("Rock")){
//You win
message = "The Computer picked Rock! You Win!";
upScore();
}
break;
case R.id.scissors_button:
if(cpuChoice.equals("Scissors")){
//Tie
message = "The Computer picked Scissors! It's a Tie!";
}
else if(cpuChoice.equals("Rock")){
//You Lose
message = "The Computer picked Rock! You Lose!";
}
else if(cpuChoice.equals("Paper")){
//You win
message = "The Computer picked Paper! You Win!";
upScore();
}
break;
}
DialogFragment dialog = WinOrLoseDialog.newInstance(message);
dialog.show(getFragmentManager(),"WinOrLose");
}
public void upScore(){
scoreCount++;
scoreView.setText("Score: " + scoreCount);
}
}
这是我的xml布局：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"
android:background="@color/dark_teal">
<Button
android:id="@+id/rock_button"
android:layout_width="200dp"
android:layout_height="50dp"
android:layout_centerHorizontal="true"
android:layout_marginTop="100dp"
android:text="@string/rock"
android:onClick="outcome" />
<Button
android:id="@+id/paper_button"
android:layout_width="200dp"
android:layout_height="50dp"
android:layout_below="@id/rock_button"
android:layout_centerHorizontal="true"
android:layout_marginTop="50dp"
android:text="@string/paper"
android:onClick="outcome" />
<Button
android:id="@+id/scissors_button"
android:layout_width="200dp"
android:layout_height="50dp"
android:layout_below="@id/paper_button"
android:layout_centerHorizontal="true"
android:layout_marginTop="50dp"
android:text="@string/scissors"
android:onClick="outcome" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/version"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
android:textStyle="bold"
android:textSize="20sp"
android:textColor="@color/white" />
<TextView
android:id="@+id/score"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:textColor="@color/white"
android:textSize="25sp"
android:textStyle="bold" />
</RelativeLayout>
答案 0 :(得分：1)
onCreate（）中的这一行造成了所有麻烦：
TextView scoreView = (TextView) findViewById(R.id.score);
您要创建并初始化局部变量，而不是初始化活动类的属性。将其更改为：
this.scoreView = (TextVoew) findViewById(R.id.score);