Prevent UI loop on low memory device

Fix #3215, close #3216

app/src/main/java/com/topjohnwu/magisk/ui/install/InstallFragment.kt

@@ -1,5 +1,9 @@
 package com.topjohnwu.magisk.ui.install
 
+import android.os.Bundle
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
 import androidx.lifecycle.viewModelScope
 import com.topjohnwu.magisk.R
 import com.topjohnwu.magisk.arch.BaseUIFragment
@@ -22,4 +26,20 @@ class InstallFragment : BaseUIFragment<InstallViewModel, FragmentInstallMd2Bindi
         BaseDownloader.observeProgress(this, viewModel::onProgressUpdate)
     }
 
+    override fun onCreateView(
+        inflater: LayoutInflater,
+        container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        viewModel._method = savedInstanceState?.getInt(KEY_CURRENT_METHOD, -1) ?: -1
+        return super.onCreateView(inflater, container, savedInstanceState)
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        outState.putInt(KEY_CURRENT_METHOD, viewModel.method)
+    }
+
+    companion object {
+        private const val KEY_CURRENT_METHOD = "current_method"
+    }
 }

app/src/main/java/com/topjohnwu/magisk/ui/install/InstallViewModel.kt

@@ -31,13 +31,16 @@ class InstallViewModel(
     var step = if (skipOptions) 1 else 0
         set(value) = set(value, field, { field = it }, BR.step)
 
+    var _method = -1
+
     @get:Bindable
-    var method = -1
+    var method
-        set(value) = set(value, field, { field = it }, BR.method) {
+        get() = _method
+        set(value) = set(value, _method, { _method = it }, BR.method) {
             when (it) {
                 R.id.method_patch -> {
                     MagiskInstallFileEvent { code, intent ->
-                        if (code ==  Activity.RESULT_OK)
+                        if (code == Activity.RESULT_OK)
                             data = intent?.data
                     }.publish()
                 }