setOnClickListener 错误 - 无法解析符号

Question

I want to create a button which, when clicked, it will show another intent.

This is the code:

   <Button
    android:text="Bine ati venit!"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/button1"
    android:background="#479fc7"
    android:textSize="40dp"
    android:textColor="@color/colorPrimaryDark"
    android:textStyle="normal|bold|italic"
    android:textAllCaps="false"
    android:fontFamily="casual"
    android:onClick="next_page"/>

and from the .java class:

    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_welcome);
}

Button button = (Button) findViewById(R.id.button1);

button.setOnClickListener( new View.OnClickListener()
{
    public void onClick (View v){
    next_page(v);
}
});

public void next_page(View v) {
    Intent intent = new Intent(this, MapsActivity.class);
    startActivity(intent);
}

I get the errors: "Cannot resolve symbol 'setOnClickListener'", "variable onClick is never used", "; expected"....

Answer 1

You should put that particular snippet inside OnCreate() . That solved the issue for me.

Answer 2

// You must move the code you type into the class method and work like the following

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        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 View.OnClickListener() {
            // The code in this method will be executed when the numbers View is clicked on.
            @Override
            public void onClick(View view) {
                Intent numbersIntent = new Intent(MainActivity.this, NumberActivity.class);
                startActivity(numbersIntent);
            }
        });
    }

Answer 3

You need to change your code like this

Button button;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_welcome); 
    button = (Button) findViewById(R.id.button1);
    button.setOnClickListener( new View.OnClickListener(){ 
        public void onClick (View v){ 
            next_page(v); 
        } 
    }); 

} 

public void next_page(View v) {
    Intent intent = new Intent(this, MapsActivity.class);
    startActivity(intent);
} 

and you don't need to pass View object to next_page() if you don't use it there

Answer 4

You either declare onClick attribute with method name in your xml or programaticaly set it in onCreate method.

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_welcome);

    Button button = (Button) findViewById(R.id.button1);

    button.setOnClickListener( new View.OnClickListener()
    {
        public void onClick (View v){
           next_page(v);
        }
    });
}

public void next_page(View v) {
    Intent intent = new Intent(this, MapsActivity.class);
    startActivity(intent);
}

Answer 5

您应该声明按钮变量并在oncreate（）函数下编写Setonclicklistner（）函数。否则它将无法正常工作。

Answer 6

With regards to the error: "Cannot resolve symbol 'setOnClickListener'" It might be worth making sure that you have imported TextView by adding

import android.widget.TextView;

to the top of your file.

Answer 7

You just need to change the location of the code.

@Override
protected void onCreate(Bundle savedInstanceState) {
 ...
 Button button = (Button) findViewById(R.id.button1);

 button.setOnClickListener( new View.OnClickListener(){
     public void onClick (View v){
     next_page(v);
     }
 });
}

Cut the Code and paste it in the OnCreate method. As it doesn't make sense to set the OnClickListener after the button is created. That's why the error occured.