java - 所有类别的点击监听器

Question

除了方法调用 setOnClickListener 可能会产生 java.lang.NullpointerException 之外，我还收到一条错误消息，指出无法解析符号 onClickListener。任何形式的帮助将不胜感激!!

公共(public)类 MainActivity 扩展 AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Set the content of the activity to use the activity_main.xml layout file
    setContentView(R.layout.activity_main);


    //Find the view that shows the numbers category
    TextView numbers = (TextView)findViewById(R.id.numbers);

    //Set a click listener on that view
    numbers.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View view) {
            //Create a new intent to open the {@link NumbersActivity}
            Intent numbersIntent = new Intent(MainActivity.this,  NumbersActivity.class);

            //Start the new activity
            startActivity(numbersIntent);
        }
                               });

    //Set button listener for the view
    //buttonView.setOnClickListener(clickListener);
}

}

Answer 1

I'm getting an error saying cannot resolve symbol onClickListener in addition to method invocation setOnClickListener may produce java.lang.Nullpointerexception

View 和 DialogInterface 类都有一个公共(public) OnClickListener 接口(interface)(还有无数的库)。您需要明确告诉编译器您想要使用哪一个:

numbers.setOnClickListener(new View.OnClickListener() {

NullPointerException 警告只是因为 findViewById() 可能返回 null。如果您确定您的 View 永远不会为 null，您可以简单地忽略警告或使用 assert 语句:

TextView numbers = (TextView) findViewById(R.id.numbers);
assert numbers != null;