今天在写Android时,发现一个错误,
`package com.example.a1104.myapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button1 = (Button)findViewById(R.id.button_1);
button1.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
Toast.makeText(this,"you clicked button1",Toast.LENGTH_SHORT).show();
}
});
}
}`
错误提示:
Cannot resolve method 'makeText(anonymous android.view.View.OnClickListener, java.lang.String, int)'
在stackoverflow上找到答案:
原因是: Toast.makeText()的第一个参数,需要时Application Context,即需要的是整个Activity,而我的代码中的“this”确是代表一个”Button“,因此报错。
Because, Toast.makeText() first argument required Application Context and in your code, this reefers to Button’s onClickListener class not a context of Activity.
改正: 把this改成整个Activity即可,
Toast.makeText(MainActivity.this ,"you clicked button1",Toast.LENGTH_SHORT).show();
//其中MainActivity 是activity的名字,用.java处的名字。