调用 OnClick 函数时 textView setText() 和 append() 崩溃

Question

我正在制作一个数独应用程序，我想添加一个移动计数器，所以我有一个 textView，每次用户输入数字时都会显示移动计数

public class NumberButton extends Button implements OnClickListener {

    private int number;
    TextView moveCountText;
    private int moves;
    private String message;

    public NumberButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOnClickListener(this);
        moveCountText = (TextView)findViewById(R.id.moveCountView);
    }

    @Override
    public void onClick(View v){
        moves++;
        message="Move Count: "+ moves;
        moveCountText.setText(message);
        moveCountText.invalidate();


        GameEngine.getInstance().setNumber(number);
    }

    public void setNumber(int number){
        this.number = number;
    }
}

麻烦的是，setText 说视图是空的（空对象），但我不知道为什么。这是 textView XML。

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="Move count: 0"
    android:id="@+id/moveCountView"
    android:layout_marginLeft="100dp"
    android:layout_marginStart="114dp"
    android:layout_marginTop="450dp"/>

我的胜利活动也是如此，错误是意图是一个空对象

public void checkGame(){
    int [][] sudGrid = new int[9][9];
    for( int x = 0 ; x < 8 ; x++ ){
        for( int y = 0 ; y < 8 ; y++ ){
            sudGrid[x][y] = getItem(x,y).getValue();
        }
    }

    if( SudokuChecker.getInstance().checkSudoku(sudGrid)){
        Toast.makeText(context, "Congratulations!", Toast.LENGTH_LONG).show();

        // opens victory screen
        Intent nextScreen = new Intent(getApplicationContext(), VictoryActivity.class);
        startActivity(nextScreen);
    }
}

这是错误信息

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                                           at sudoku.view.buttonsgrid.NumberButton.onClick(NumberButton.java:33)
                                                                           at android.view.View.performClick(View.java:5156)
                                                                           at android.view.View$PerformClick.run(View.java:20755)
                                                                           at android.os.Handler.handleCallback(Handler.java:739)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                           at android.os.Looper.loop(Looper.java:145)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5832)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at java.lang.reflect.Method.invoke(Method.java:372)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

还有 XML

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="Move count: 0"
    android:id="@+id/moveCountView"
    android:layout_marginLeft="100dp"
    android:layout_marginStart="114dp"
    android:layout_marginTop="450dp"/>

Answer 1

你每次设置文本时 moveCountText 为空。

改变这个-

setOnClickListener(this); 
moveCountText =(TextView)findViewById(R.id.moveCountView);

到-

moveCountText =(TextView)findViewById(R.id.moveCountView);
moveCountText.setOnClickListner(this);

并实现 View.OnClickListner 会为你工作:)