安裝生成工具25.0.3錯誤顯示在Android工作室，當我試圖運行我的舊安卓項目

Question

我卸載並安裝了再次安裝工作室由於在構建gradle上的一些錯誤。我已經創建併成功運行的項目，是現在不是我目前安裝studio.It紅印工作線AppCompatActivity，findViewById，startActivity等

完整的Java文件如下

package com.example.mfk.simpleloginapp; 

import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.widget.Toast; 

public class Login extends AppCompatActivity { 
    private static EditText username; 
    private static EditText password; 
    private static TextView attempts; 
    private static Button login_btn; 
    int attempt_counter = 5; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_login); 
     LoginButton(); 
    } 

    public void LoginButton() 
    { 
     username = (EditText)findViewById(R.id.editText4_Enter_UN_Here); 
     password = (EditText)findViewById(R.id.editText3_Enter_PW_Here); 
     attempts = (TextView) findViewById(R.id.editText5_Attmpts_see_here); 
     login_btn = (Button)findViewById(R.id.button2_Login); 

     attempts.setText(Integer.toString(attempt_counter)); 

     login_btn.setOnClickListener(new View.OnClickListener() 
     { 

      @Override 
      public void onClick(View v) 
      { 
       if(username.getText().toString().equals("mohammedfarisk")&&password.getText().toString().equals("farisk321@android")) 
       { 
        Toast.makeText(Login.this,"Username and Password are correct",Toast.LENGTH_SHORT).show(); 
        Intent intent = new Intent("com.example.mfk.user.User"); 
        startActivity(intent); 
       } 
       else 
       { 
        Toast.makeText(Login.this,"Username or Password is NOT correct",Toast.LENGTH_SHORT).show(); 
        attempt_counter--; 
        attempts.setText(Integer.toString(attempt_counter)); 
        if(attempt_counter == 0) 
        { 

         login_btn.setEnabled(false); 
        } 
       } 
      } 
      }); 
    } 
    @Override 
    public boolean onCreateOptionsMenu(Menu menu) 
    { 
     //inflates the menu ; this adds items to the acion bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_login, menu); 
     return true; 
    } 
} 

Answer 1

如果沒有選擇自動安裝它，看對於此按鈕： （SDK Manager）。