Question

在Android Studio java类中声明按钮的最佳方法是什么？例如，我有按钮＆amp;文字字段：

TextView t = (TextView) findViewById(R.id.Question);
TextView A = (TextView) findViewById(R.id.AnswerA);
TextView B = (TextView) findViewById(R.id.AnswerB);
TextView C = (TextView) findViewById(R.id.AnswerC);
TextView D = (TextView) findViewById(R.id.AnswerD);
Button next_test = (Button)findViewById(R.id.Next_Text);
Button b = (Button)findViewById(R.id.button);

当我在类下面声明它们时，Android Studio会抛出错误：

public class main extends AppCompatActivity {

TextView t = (TextView) findViewById(R.id.Question);
TextView A = (TextView) findViewById(R.id.AnswerA);
TextView B = (TextView) findViewById(R.id.AnswerB);
TextView C = (TextView) findViewById(R.id.AnswerC);
TextView D = (TextView) findViewById(R.id.AnswerD);
Button next_test = (Button)findViewById(R.id.Next_Text);
Button b = (Button)findViewById(R.id.button);

@Override
protected void onCreate(Bundle savedInstanceState) {..........

当我在需要的方法中声明它们时，它不会抛出错误，但是我必须多次声明它们并在oncreate中声明final。

有没有办法只宣告一次？

Answer 1

您的成员变量应该可以在您的班级内全局访问。但如果xml没有膨胀，你就无法通过id找到一个视图。这就是你的代码应该是这样的：

public class main extends AppCompatActivity {

TextView t;
TextView A; 
TextView B;

@Override
protected void onCreate(Bundle savedInstanceState) {
        setContentView(R.layout.your_layout); // THIS IS VERY IMPORTANT

t = (TextView) findViewById(R.id.Question);
A = (TextView) findViewById(R.id.AnswerA);
B = (TextView) findViewById(R.id.AnswerB);
....
}

方法findViewById在R.layout.your_layout中查找您的视图...如果您不调用setContentView()，它将找不到任何内容并返回null。希望它有意义:)）

Answer 2

申报意见的正确方法：

columns.Add(new DataGridViewTextBoxColumn() {CellTemplate = new MyDataGridViewTextBoxCell()});

这适用于所有视图，如button，imageview，linearlayout，imageview等....

Answer 3

你可以这样做

public class main extends AppCompatActivity {

   private TextView t;
   private TextView A;
   private TextView B;
   private TextView C;
   private TextView D;
   private Button next_test;
   private Button b;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initialize();
   }

   private void initialize(){
        t = (TextView) findViewById(R.id.Question);
        A = (TextView) findViewById(R.id.AnswerA);
        B = (TextView) findViewById(R.id.AnswerB);
        C = (TextView) findViewById(R.id.AnswerC);
        D = (TextView) findViewById(R.id.AnswerD);
        next_test = (Button)findViewById(R.id.Next_Text);
        b = (Button)findViewById(R.id.button);
   }

Answer 4

在OnCreate方法

中声明它们

public class main extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {  
super.onCreate(savedInstanceState);
setContentView(R.layout.your_activity_layout);
TextView t = (TextView) findViewById(R.id.Question);
TextView A = (TextView) findViewById(R.id.AnswerA);
TextView B = (TextView) findViewById(R.id.AnswerB);
TextView C = (TextView) findViewById(R.id.AnswerC);
TextView D = (TextView) findViewById(R.id.AnswerD);
Button next_test = (Button)findViewById(R.id.Next_Text);
Button b = (Button)findViewById(R.id.button);
.....
}

您应该始终在onCreate方法中初始化它们并放在

之后

 setContentView(R.layout.your_activity_layout);

Answer 5

您必须在onCreate中声明您的观看次数。将findViewById方法放在onCreate。

中

在android工作室中声明按钮

5 个答案: