Android-尝试创建ImageView数组并在代码中添加可绘制资源

Question

我正在尝试创建一个ImageView控件数组，并向其中添加可提取资源

由以下原因引起：java.lang.NullPointerException：尝试调用虚拟方法"void android.widget.ImageView.setBackgroundResource（int）"空对象引用

这是代码：

public class MultipleChoice extends ActionBarActivity {
    TextView Left;
    TextView Operator;
    TextView Right;
    TextView GameTimer;
    TextView CorrectAnswers;
    ImageView imageView[] = new ImageView[11];
    int imageViewNumber;
    Button btnStart;
    int intLeft;
    int intOperator;
    int intRight;
    int intCorrectAnswer;
    int intCorrectAnswers;
    String strCorrectAnswer;
    CountDownTimer problemtimer = new CountDownTimer(10000,1000) {
        @Override
        public void onTick(long millisUntilFinished) {
        }
        @Override
        public void onFinish() {
            NextProblem();
        }
    };
    CountDownTimer gametimer = new CountDownTimer(60000,1000) {
        @Override
        public void onTick(long millisUntilFinished) {
            GameTimer.setText("Time Left: " + millisUntilFinished / 1000);
        }
        @Override
        public void onFinish() {
            problemtimer.cancel();
            gametimer.cancel();
            GameTimer.setText("Time Left: 0");
            btnStart.setEnabled(true);
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_multiple_choice);
        SetStartupValues();
    }
    private  void SetStartupValues(){
        Left = (TextView) findViewById(R.id.Left);
        Operator = (TextView) findViewById(R.id.Operator);
        Right = (TextView) findViewById(R.id.Right);
        GameTimer = (TextView) findViewById(R.id.Timeleft);
        CorrectAnswers = (TextView) findViewById(R.id.CorrectAnswers);
        btnStart = (Button) findViewById(R.id.btnStart);
        Left.setText("");
        Operator.setText("");
        Right.setText("");
        GameTimer.setText("Time Left: 60");
        CorrectAnswers.setText("Correct: 0");
        intCorrectAnswers = 0;
    }
    @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 btnStart_Click(View view) {
        // Do something in response to button click
        SetStartupValues();
        NextProblem();
        gametimer.start();
        btnStart.setEnabled(false);
    }
    public void  NextProblem(){
        intLeft = new Random().nextInt(100);
        intRight= new Random().nextInt(100);
        intOperator= new Random().nextInt(3);
        Left.setText(String.valueOf(intLeft));
        Right.setText(String.valueOf(intRight));
        imageViewNumber=0;
        switch(intOperator){
            case 0:
                Operator.setText("+");
                intCorrectAnswer = intLeft + intRight;
                break;
            case 1:
                Operator.setText("-");
                intCorrectAnswer=intLeft-intRight;
                break;
            case 2:
                Operator.setText("X");
                intCorrectAnswer=intLeft*intRight;
                break;
        }
        strCorrectAnswer = String.valueOf(intCorrectAnswer);
        GetNumbers(strCorrectAnswer);
        problemtimer.start();
    }
    private void GetNumbers(String strNumber){
        LinearLayout ll = (LinearLayout)findViewById(R.id.linearLayout1);
        int L = strNumber.length();
        String c;
        for (int i = 0;i<L-1;i++){
            c=strNumber.substring(i,i+1);
            switch (c){
                case "1":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.one);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "2":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.two);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "3":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.three);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "4":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.four);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "5":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.five);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "6":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.six);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "7":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.seven);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "8":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.eight);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "9":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.nine);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                case "0":
                    imageView[imageViewNumber].setBackgroundResource(R.drawable.zero);
                    ll.addView(imageView[imageViewNumber]);
                    break;
                }
            }
        }

错误发生在类似的线路上的Switch语句中

imageView[imageViewNumber].setBackgroundResource(R.drawable.zero);

我做错了什么？

这是我的布局文件

<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=".MultipleChoice"
android:minWidth="30dp"
android:focusableInTouchMode="false">
<TextView android:text="@string/LeftText" android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/Left"
    android:layout_below="@+id/Timeleft"
    android:layout_toLeftOf="@+id/Operator"
    android:layout_toStartOf="@+id/Operator" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/OperatorText"
    android:id="@+id/Operator"
    android:layout_below="@+id/Timeleft"
    android:layout_centerHorizontal="true" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/RightText"
    android:id="@+id/Right"
    android:layout_below="@+id/Timeleft"
    android:layout_toRightOf="@+id/Operator"
    android:layout_toEndOf="@+id/Operator" />
<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/StartButton"
    android:id="@+id/btnStart"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:onClick="btnStart_Click"
    android:enabled="true"
    android:focusable="false" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/TimeLeft"
    android:id="@+id/Timeleft"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Correct: 0"
    android:id="@+id/CorrectAnswers"
    android:layout_alignTop="@+id/Timeleft"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/LinearContainer"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:baselineAligned="false">
        <LinearLayout
        android:orientation="horizontal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/linearLayout1"
            android:layout_weight="1"
            android:gravity="center_horizontal">
        </LinearLayout>
        <LinearLayout
            android:orientation="horizontal"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/linearLayout2"
            android:gravity="center_horizontal">
        </LinearLayout>
        <LinearLayout
            android:orientation="horizontal"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/linearLayout3"
            android:gravity="center_horizontal">
        </LinearLayout>
    </LinearLayout>
</RelativeLayout>

Answer 1

您的"imageView"数组中没有对象。

用值初始化：

for(int i = 0; i < imageView.lenght; i++) imageView[i] = new ImageView(context);

所以你可以正确使用。