在send方法中,应该先获取EditText控件的引用,然后再获取其文本内容。正确的代码应该是:
public void send(View view) {
et_receiver = findViewById(R.id.et_receiver);
et_content = findViewById(R.id.et_content);
String receiver,message;
receiver=et_receiver.getText().toString();
message=et_content.getText().toString();
Intent intent = new Intent();
intent.setAction(intent.ACTION_SENDTO);
intent.addCategory("android.intent.category.DEFAULT");
intent.setData(Uri.parse("sms:"+receiver));
intent.putExtra("sms_body",message);
startActivity(intent);
}