android获取控件的几种方式

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:background="@color/colorPrimary"
    android:layout_height="wrap_content">
    <TextView
        android:id="@+id/item_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textSize="25sp" />
</RelativeLayout>

private TextView item_tv;

item_tv = findViewById(R.id.item_tv);
item_tv.setText("text1");

int viewId = getResources().getIdentifier("item_tv", "id", getPackageName());
TextView textView =findViewById(viewId);
textView.setText("text2");

try {
    Field field = R.id.class.getField("item_tv");
    TextView textView = findViewById(field.getInt(null));
    textView.setText("text3");

} catch (NoSuchFieldException e) {
    e.printStackTrace();
} catch (IllegalAccessException e) {
    e.printStackTrace();
}

java反射机制
    获取类的方式:(1)class.forName("类名"),(2)类名().getClass(),(3)类名.class;
    Constructor类:
        getConstuctor()返回class的构造函数;
        getConstructors()返回class类的所有构造方法;
        getDelaredConstructor()返回class类或接口指定的构造函数;
        getDelaredConstructors()返回所有class类或接口指定的构造函数;
        getEnclosingConstructor()返回class类的构造方法中的一个本地或匿名类;
        getModifiers()返回对象的java修饰符;
        getName()以字符串的形式返回构造方法的名称;
        newInstance()实例化对象;
    getDeclaredFields()获取本类的全部属性;
    getMethod()获取类中的方法对象;
    Field类:
        获取反射字段的方式:getDeclaredField(),getFields();
        getName()获取字段名;
        getType()获取字段类型;
        get()获取字段的值;
        set()设置字段的值;

try {
        Class stuClass = Class.forName("com.example.homepage.activity.HH");
        Field file = stuClass.getDeclaredField("item_tv"); // 通过反射获取item_tv对象
        file.setAccessible(true);
        TextView textView = (TextView) file.get(this); // 获取textView实例
        textView.setText("text4");
        file.set(this,textView);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

        try {
//            Field field = R.id.class.getField("header_tv");
            Class stuClass = Class.forName("com.jwenfeng.library.pulltorefresh.view.HeadRefreshView");
//            Class stuClass = Class.forName("com.jwenfeng.library.pulltorefresh.PullToRefreshLayout");
//            Field f = stuClass.getDeclaredField("header_tv");
//            f.setAccessible(true);
//
//            TextView textView = findViewById(f.getInt(null));
//            Log.e("tea",textView.getText().toString());
//            textView.setText("zezeze");
//            HeadRefreshView view = (HeadRefreshView) stuClass.newInstance();
//            Field[] fieldArray = stuClass.getFields(); // 不包括私有参数
//            Field[] fieldArray = stuClass.getDeclaredFields(); //私有参数
//            for(Field f : fieldArray){
//                Log.e("tea", String.valueOf(f));
//            }
            Field file = stuClass.getDeclaredField("tv");
            file.setAccessible(true);
//            Log.e("tea", String.valueOf(file));
            HeadRefreshView view = new HeadRefreshView(this);
            TextView nameStr = (TextView) file.get(view);
            Log.e("tea", nameStr.getText().toString());
            nameStr.setText("tea9");
//            nameStr.setVisibility(View.GONE);
//            TextView textView = new TextView(this);
//            textView.setVisibility(View.GONE);
//            textView.setText("tea0");
//            file.set(view, nameStr);
//            Constructor<?>[] constructor = stuClass.getConstructors(); //构造方法
//            for (int i = 0; i < constructor.length; i++) {
////                Log.e("tea", constructor[i].toString());
//            }
//            Method[] methods = stuClass.getDeclaredMethods(); // 获取声明的方法
//            for (int i = 0; i < methods.length; i++) {
////                Log.e("tea", methods[i].toString());
//            }
            Method m2 = stuClass.getDeclaredMethod("getView");
            View view1 = (View) m2.invoke(view);
            TextView textView1 = view1.findViewById(R.id.header_tv);
            textView1.setVisibility(View.GONE);
            textView1.setText("tea8");
            file.set(view1, textView1);
//            Log.e("tea1", textView1.getText().toString());
//            TextView nameStr1 = (TextView) file.get(view);
//            Log.e("tea", nameStr1.getText().toString());

        }  catch (Exception e) {
            e.printStackTrace();
            Log.e("tea", "错误了");
        }

//        int viewId = getResources().getIdentifier("tv", "id", "com.jwenfeng.library.pulltorefresh");
//        TextView textView = (TextView)findViewById(viewId);
//        textView.setText("sss");