activity跳转

创建activity的界面布局以及跳转应用

代码简单，但是不注意会有闪退问题。页面跳转后出错

第一个xml

第二个xml

第一个java

public class MainActivity extends AppCompatActivity {
private EditText ev_username;
private Button btn_jrpg;
private Button btn_tc;
private TextView jgh;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ev_username=(EditText)findViewById(R.id.ev_username);
btn_jrpg=(Button)findViewById(R.id.btn_jrpg);
btn_tc=(Button)findViewById(R.id.btn_tc);
jgh=(TextView)findViewById(R.id.jgh);
String date="";
Intent intent=getIntent();
String jg=intent.getStringExtra("result");
TextView jgh=(TextView)findViewById(R.id.jgh);
date= jg;
jgh.setText(date);

}
public void onClick(View view){
switch (view.getId()) {
case R.id.btn_jrpg:
entry();
break;
case R.id.btn_tc:
finish();
break;
}}
private void entry(){
Intent intent=new Intent(MainActivity.this,Main2Activity.class);
String text = ev_username.getText().toString();
intent.putExtra("name",text+ ":对学习java有没有信心？");
startActivity(intent);
}
}

第二个java

public class Main2Activity extends AppCompatActivity {
private Button btn_y;
private Button btn_n;
private TextView xx;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
btn_n=(Button)findViewById(R.id.btn_n);
btn_y=(Button)findViewById(R.id.btn_y);
xx=(TextView)findViewById(R.id.xx);
String data="";
Intent intent=getIntent();
String jg=intent.getStringExtra("name");
TextView question=(TextView)findViewById(R.id.xx);
data = jg;
question.setText(data);
}
public void onClick(View view){
switch (view.getId()) {
case R.id.btn_y:
answer();
break;
case R.id.btn_n:
answer2();
break;
}}
private void answer(){
Intent intent=new Intent(Main2Activity.this,MainActivity.class);
String text = xx.getText().toString();
intent.putExtra("result", ":对学习安卓有信心");
startActivity(intent);
finish();
}

private void answer2(){
Intent intent=new Intent(Main2Activity.this,MainActivity.class);
String text = xx.getText().toString();
intent.putExtra("result", ":对学习安卓没有信心");
startActivity(intent);
finish();
}
}